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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: MarcoK75c on July 11, 2017, 10:16:34 PM
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After having read old dry germanic service bulletins and searched here I am just slightly confused....
The attached drawing shows a routing for the tank vent hose that goes from a nipple on the fuel pump suction to a "knobby" connector on the roof just behind the gas cap. I understand the routing but I am perplexed. After diving into the tank a few days ago to replace the fuel filter & $30 hose, I found a decrepit old piece of tubing dangling from the top "knob".... Here are my questions:
- Why does this vent need to go to the nipple on the pump suction?
- This set-up puts the tube below fuel level, if my tank get pressurized because of heat, would this not just force fuel out of my drain and start a nice siphon effect?
- Does the knobby connector have a function I do not understand?
Thanks!
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That little hose from the pump bottom to the top of the tank is supposed to do something when the fuel boils. Fuel boiling was a problem on the early Ks. BMW added under tank insulation and air scoops and I have not heard of fuel boiling lately.
I have run mine with and without the hose(without now) with no problems.
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Carefully examine the pictures below of a cut-away K100 tank:
(https://lh3.googleusercontent.com/vpPL1Ob7jzZG6uZFEo5iQ_QP24QJFdKQ2oQuk8Dkstk0xY2HnMkIRPYniC2zAXBvDNYlbbck9BspxFYnWF7poYEp_t4DJYO2Xa1oebVmxWK46eG2Mgsm_qsvgKH09E2ARfD-0JgkJ-3Y9mUXZmT9nAhw0rNXDI75-ly8JwgHCj0ct7qkOBZ48fXvyPfBNGknRblsXy5PQoAuYOMBevyySaCa1uNAilkOEsNInHkLhbdMPHQPR26a-ufKTMYWCv9dCDJTApJ-ofY7pXBzzR2hX_D9Y_ggr92FZPHiNDRXJRQ9r7FAtAFZyi9Xdhh_uPhLa3jI16UFDqJuGxNgyKF_ijVYCePfKWiWNnST4_IhOK3pUySING8M2WPy8kMGMcbb0TlbCa0ymFLVnT8Uf7VNg36fS1uOlwCQO1a_Vd87-ijF72dTguU59NThT1_cl3NIqOnWqgFBkm0QzvDSaY6AqC_rRP2Uhf1ryxCnWfLITcoVc8E8ADF2DgOT4Dk67ZQFZS3Q8umsw-h8YQHQdLiAowFvXRD-67QtjzLnx8w1FcBAsP7dtw8kSAfkjMwP2LNE8-1OsmwtsFxUYv6lk97NUZ9zVGXyt3RJSjMTiCZ4yoWS39EzWqCQsCL-YehcZvSMso5Uu1_nffkBd5T-55ATeXuVQpH983WoqGPJKbtsmsujHQ=w1000-h667-no)
(https://lh3.googleusercontent.com/k3BFZSNnP1fPq6vTvsgeKvmZ0Ia1UH53xO-0XMpVbs_UB6k0tFnVp6klnMUyfMKPzEY2AcH7m7c5vm-a-Yn_saTNKXZGvVx9Fp1PVKZLP39J3jrRz71Q7DpObyQSoOwGnYdYCiMoNEcIyVIpg-jZXxaLq8EsLEMdutkyrc4o0HuF3EC3GSTSRUi8Y8lqGSnHkRDPdrP09nXdyUdcBpgWZz14ZZDHwqID0jYH4iYTCJlLVZ0Ai5cF4DpKrBgX3AXuezZ4gK7A-Fecn-zm6A_VG4_CQ6Ogh-fAKvIF0A5ghpYmxSXlMaL6tJA1xXjyQLh4SvU--x6b9QtrGdt1Pw7Bx3D74aVzzGo_oh4K3j-NV6Yl7RN4_KWx5TlJfO8VjjMig9jPPOnYb0sRP1nTt7Vcx79Wg-AW5jmHoTklP-cdRgmKkaCUo2mSFhRYrDgvO90ftk6a4GXbLbA-r-tmHW554HGvuaOwt_72YHs_6Iw5MCbbNW8LA23qvIapCx1A9j7aNHn7lDyWIB7OqLFomSR1kkmWUsbfeYwmRAZzu0DMprse2NhVYGmrJ8p5bQQoRhacV9kVbrbkzEUwf-Uy7f8FMzmKrTX6D5gjpsdcpmXSZbLcqTJ7vvM-4t7s284xa5XH3lkUniKAOqDoVQ0Xbb7FzxnqQwX0nTdxVWZHErCJfV1MfQ=w764-h1024-no)
The following annotated version of the above picture was kindly provided by Laitch later in this thread, around post 55:
(http://www.motobrick.com/gallery/1/1601-220219172759.png)
The pipe you refer to is evident on the inverted top section of the cut-away tank and more clearly illustrated in the detail photo. You can see the fuel return line routing behind the collector unit and leading to a small spigot. You can also see the two vent lines, one of which is attached to that cylindrical collector, the other of which is attached to the gas cap mounting ring. The pipe you point out in the first post is one of these vent lines. The hose to which MarcoK75c refers is normally connected between that spigot you see pointing upwards and the filter basket surrounding the fuel pump. This hose connection is to prevent cavitation and improve fuel flow. If it is missing, returning fuel just pours out the spigot into the tank.
Why does this vent need to go to the nipple on the pump suction? To prevent cavitation at the pump inlet.
This set-up puts the tube below fuel level, if my tank get pressurized because of heat, would this not just force fuel out of my drain and start a nice siphon effect? No. There is no direct connection between the overflow drain pipe and that return supply hose.
Does the knobby connector have a function I do not understand? It's where the return fuel exits.
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Carefully examine the pictures below of a cut-away K100 tank:
Does the knobby connector have a function I do not understand? It's where the return fuel exits.
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My tank is an older (?) Design, the return fuel simply exits in the upper left of the tank (at the other knobby) and then flows down to the pump. I watched it do this with some cellophane in place of the cap while on the center stand.
The other knobby replaces the burrito in the cut away, but only two connectors going into it, one hard tubing to the drain, the other the tubing in question.
Sent from my iPhone using Tapatalk
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My 1986 K75c has the same tank shown in the photo.
Sounds like in yours the hard pipe may be cut / removed similar to the red lines I've added. :dunno
The line should be a solid pipe up to the top of the tank then turned down and the flexible line (circled - pic is kinda deceiving because the loose end is hidden behind that baffle) would then be attached to the "out" arrow.
The "burrito" should only have one vent pipe actually plumbed to it - overflow. The return line goes beside the burrito but doesn't actually connect internally. The other vent goes to the filler cap ring to drain water. (Why you should never turn the orientation of the filler cap.)
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Well, a more careful reading of the Haynes manual has confirmed my suspicions that the routing along the inside of the tanks was changed in mid 1986:
From page 135:
"12 With the introduction of the k75 S models in mid-1986 the return valve was deleted completely and replaced by a long stack pipe which passes up to the top of the tank"
This confirms I have the early version of the tank, long return pipe and a knobby connector instead of the burrito.
I went out, pulled the pump, accessed the mesh screen with a hose nipple connection, connected the rubber hose in accordance to the dwgs and mounted everything carefully back together. Started it up and wow...most of the cicadas have left my tank and I can hear only one or two at most now!
Thanks for the help!
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This confirms I have the early version of the tank, long return pipe
This should read "NO long return pipe"
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Hi, sorry to resurrect an old thread, however it contains info, that helped me a lot so far but some other details are still murky in my muddled up brain :) So as I have posted yesterday in the 'what did you do...' thread I am trying to find out, why there is this loud hissing noise coming from the tank. I have done two short videos, where it looks like, the petrol is not coming out of the barbed pipe on the left hand side, but an another line at the other end of that burrito (I love that description :) ). Am I correct to think, the returning petrol should be routed inside the burrito collector and come out of the barbed pipe in order to be routed back with an immersible line to the bottom of the fuel pump?
The videos ->
https://www.youtube.com/watch?v=dnuuOTk2HrY
https://www.youtube.com/watch?v=UCG4aEAgHaI&feature=youtu.be
Thanks!
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It's much clearer after a close look at rbm's post. I'm thinking the return pipe does not go into the burrito but beside it. I think attaching a hose to divert it will fix the noise problem. It should be an easy test.
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Actually, maybe someone was very rough and bent the end of the return pipe towards the right side. That's my new best guess, I better leave it at that now.
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Actually, maybe someone was very rough and bent the pipe towards the right side. That's my new best guess, I better leave it at that now.
Dave, thanks for the suggestions. The pipe, which is pointing straight down and has got a barb at the end is on the other side, but there is no petrol coming out of it, it visible at the beginning of the first video. The line, petrol is coming out of does not look to be severed or damaged, so probably it was cut. As I do not have a detailed schematics, I am not sure what goes where, Robert's pictures do help a ton, but I still not see, where the return line is connected to, e.g. if it is indeed routed to the collector or not (although that would be logical, otherwise what would be the point of it). If petrol level lowers somewhat, I might try to film the bottom and back side of the burrito, but being a bit more careful this time, as Soggz is right and poking electronic devices in petrol fumes is probably stupid...
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While we're on the topic of tanks, I ordered one of these stop valves to prevent fuel from streaming out the hose when I pulled it off the tank, as discussed in this thread:
http://www.motobrick.com/index.php/topic,6200.msg41288.html#msg41288
I got the valve from Bike Bandit and it's supposed to be the replacement for the OEM part shown.
Unfortunately it's not shown in that cutaway, and if you look at the tank from below where the valve's nipple protrudes, it appears to be welded in there. Does anyone have any experience with this? If so, I'll start another thread -- the issue has come up several times in the past few years, and for me it's not a dribble anymore, but a stream -- it only took a couple hours to drain 2.5 gallons of fuel through the outlet, whereas there should actually be no fuel coming out of there at all.
BTW please refrain from discussing workarounds such as clamping off or plugging the hose. I've been doing that -- what I need now is someone who knows how to replace that valve while I have the tank off and drained for maintenance.
Many thanks in advance --
MH
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Am I correct to think, the returning petrol should be routed inside the burrito collector and come out of the barbed pipe in order to be routed back with an immersible line to the bottom of the fuel pump?
That is incorrect. The the short barbed pipe adjacent to the burrito collector is a vent pipe attached to the filter basket via a hose. The hose that attaches the two is not a high pressure fuel hose, it is a submersible vent hose.
(http://www.motobrick.com/gallery/1/1601-200219081957.png)
(http://www.motobrick.com/gallery/1/1601-200219082047.png)
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That is incorrect. The the short barb pipe adjacent to the burrito collector is is a vent pipe attached to the filter basket via a hose. The hose that attaches the two is not a high pressure fuel hose, it is a submersible vent hose.
(http://www.motobrick.com/gallery/1/1601-200219081957.png)
(http://www.motobrick.com/gallery/1/1601-200219082047.png)
Oh OK, thanks Laitch for clarification. Is that hose necessary? I do not have it in the tank, but it is cheap enough to replace if it makes the bike running better
On the other note, what about that pipe, that is streaming fuel? Is that normal or something out of place?
Thanks!
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Motorhobo is fuel drain out when the tank is off your bike? If it's draining when all connected, is it draining out the exhaust? If so I'd guess injector not closing.
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It drains when the tank is off the bike.
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I spose it's siphoning
I spose it would stop if you put your finger oven the vent outlets
One of my bikes does that, I just put a rubber plug on it, since it's just temporary while your working on it.
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You have a neglected relic that has undergone 16th century diagnosis and treatment technique during its lifespan. Chances are the return pipe was plugged and cutting it was the solution. It's difficult to determine from here. Some owners have left the fuel basket unconnected to that short, barbed pipe without any ill effect on performance. I'm one of them. If you believe your enjoyment of this moto is being hampered by an ancestral curse, connect it.
The basket-vent hose-vent pipe scheme was obviated when the system was converted to a 43mm diameter pump using a fuel sock. By its construction, the fuel sock prevents air from entering the pump and causing malfunction. The basket-hose system channels air from the fuel stream before it can enter the pump.
Concerning the fuel return streaming from the pipe—adapt to it. It's the fuel return pipe. A submersible fuel hose could be clamped to it then routed downward. The extension could even dump toward the rear left-side of the tank by using hose of sufficient length then securing it to one of the vent pipes with a zip tie. This was a solution offered up by BMW when some owners complained that the tanks were prematurely running low on fuel and the pumps were whining because fuel was being dumped away from the fuel pump.
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Unfortunately it's not shown in that cutaway, and if you look at the tank from below where the valve's nipple protrudes, it appears to be welded in there.
You might have been sent an incorrect part. That should be a screw fitting (https://www.turnermotorsport.com/p-44767-16121455348-genuine-bmw-part/). I notice that number has been applied to vents that are clamped to hoses on either end, too.
Here's an extract of Haynes' instructions for working with that valve.
(http://www.motobrick.com/gallery/1/1601-200219093201.png)
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Sorry, shouldn't have suggested plugging it, was early hours, was running on auto pilot.
I spose your not interested in Inge's idea of cranking it with the fuse removed, before removing the tank?
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You have a neglected relic that has undergone 16th century diagnosis and treatment technique during its lifespan. Chances are the return pipe was plugged and cutting it was the solution.
Concerning the fuel return streaming from the pipe—adapt to it.
Laitch, undestood, that was something, I have considered doing after reading the initial thoughts on this old thread (I hijacked, sorry for that). However Gryphon's sentence of the burrito being there for fuel saving, and me having awful mileage made me think, if the two are anyhow related (as everything else to try is exhausted, temp sensor reads fine, valves are not tight anymore, throttle bodies synced, no air leaks, new plugs, injectors cleaned)
So how I could revert to the old ways, e.g. fuel return line connected to the collector (if that indeed is the place, it is normally routed to)? The reason, I am somewhat baffled is that if you are correct, and the the barbed pipe is only for air exhaust there is no other outlet from the burrito fuel to escape to. There is a tiny hole on the bottom, that could not dump enough fuel and the overflow line obviously, but that would mean raw fuel being puked onto the pavement at 25-30PSI... Or is there another outlet, I am not aware of?
Thanks!
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You might have been sent an incorrect part. That should be a screw fitting (https://www.turnermotorsport.com/p-44767-16121455348-genuine-bmw-part/). I notice that number has been applied to vents that are clamped to hoses on either end, too.
Here's an extract of Haynes' instructions for working with that valve.
(http://www.motobrick.com/gallery/1/1601-200219093201.png)
Thanks, Laitch -- that part with the screw fitting is exactly the one I have. I'll take a look at it and see if I can make sense of what the Haynes says, and start another thread...didn't want to hijack this one, but looking at it from the bottom, it made no sense to me how it's supposed to go in there.
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Look closely at rbm's photo, the pipe from the burrito exits the tank at the rear, right underside of the tank, its for air, not fuel.
The photo shows the fuel return pipe roughly parallel with the burrito, but your's has possibly been cut.
I took gryph's post as a joke as if you get gas if you eat a burrito.
Maybe give your bike a full service and do the air fuel ratio test, it takes all of ten seconds.
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In the photo the return pipe goes behind the burrito, then parallel with it, then pops up on the left.
That's how it is supposed to be. And then a hose from there to beside the pump. But yours is not normal.
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Most of your response was incomprehensible to me. Gryph was joking in his comment but the joke apparently was lost in translation.
I can't answer if there is another outlet of which you are unaware because I'm unsure of the state of your awareness. What I can observe is fuel returning to the tank. It seems you don't like the noise it makes. I've explained what you might do to mitigate that. That's all I've got.
Laitch, the joke was not lost on me, but I thought it was just a funny afterthought for a true statement (e.g. fuel saving). You must understand my frustration, as I have done everything in the sodding book to lower my fuel consumption, but it is a no-go, and in the winter I was getting 29-30MPG, which is awful even for our family car, let alone for a bike, that supposed to be frugal on petrol. I am not a boy racer type and never drive the bike doing 100MPH, so I don't get it.
As to the other thing, I understood your solution how to mitigate the noise, and thanks for the reply, however I tried to find out what happens to the fuel if it enters that burrito as it must exit also, but where?
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. . . I have done everything in the sodding book . . .
You haven't written that you have adjusted the valve clearances, only that you intend to do so. You haven't written that you determined why one throttle body needs significantly more adjustment than the others according to your bottle manometer. You haven't written that you've done a thorough test of the coolant temperature sensor, or have you? You haven't written that the Hall Sensor is correctly aligned, or have you? You haven't written that you've checked the condition of the spark plugs after one of these low mpg rides, or have you? Have you determined the fuel pressure? Is it warm enough in the Motherland to do these tests yet? If fuel puddling isn't onto the floor while the engine is running, the fuel path seems intact.
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You haven't written that you have adjusted the valve clearances, only that you intend to do so. You haven't written that you determined why one throttle body needs significantly more adjustment than the others according to your bottle manometer. You haven't written that you've done a thorough test of the coolant temperature sensor, or have you? You haven't written that the Hall Sensor is correctly aligned, or have you? You haven't written that you've checked the condition of the spark plugs after one of these low mpg rides, or have you? Have you determined the fuel pressure? Is it warm enough in the Motherland to do these tests yet? If fuel puddling isn't onto the floor while the engine is running, the fuel path seems intact.
HI Laitch, yes, I did some of the above, valve clearances were sorted over the winter as were the injectors. The coolant temp sensor was checked as a first thing back in September at the computer, as recommended by you and the others. I can not check it now, as it is still a tad cold outside to get the bike boiling over (top daytime temp is 10-15C). The spark plugs are OK, tan coloured with a very slight hint of white. As to why there is difference in throttle bodies is unknown to me, most likely because the butterflies open slightly differently, but Gryphon has got the same situation and his bikes are running fine. Fuel pressure has not been done, neither was compression, as I am still waiting for the slow boat from China. Hall Sensor was not touched, as a failing one would give me all sorts of driveability problems, wouldn't it? So yes, you are right, everything was not checked. All the external fuel lines were replaced by me, so I hope, there will not be any puddling in the near future :)
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Look closely at rbm's photo, the pipe from the burrito exits the tank at the rear, right underside of the tank, its for air, not fuel.
The photo shows the fuel return pipe roughly parallel with the burrito, but your's has possibly been cut.
I took gryph's post as a joke as if you get gas if you eat a burrito.
Maybe give your bike a full service and do the air fuel ratio test, it takes all of ten seconds.
Daveson, I am still confused, sorry I am just thick at times... I have made a picture, I will attach, maybe you could explain to me, what you have meant, as I am at loss. As I understand, the narrow pipe, that is coming out of the burrito is for fuel vapours exiting the tank. That line was at the beginning of K production connected to the crankcase, at a later date that connection was omitted and both outlets - water drain from the filler hole and the fuel vapour drain were directed into the plastic cup, that is sitting on the frame, just below the tank and the narrow nipples protruding from it. The barbed pipe might not even enter the burrito, hard to tell from the pics and unfortunately I can not see that in detail even on the bike. It is very obvious, somebody has done something the the pipes on my bike, but I do not know what, as I was looking and feeling around, if I notice a cut line coming from the burrito, but I could find none. I might even obsess over something, that is not important, if that is the case, I am sorry for that...
Now for the pic>
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The fuel return does not enter the burrito. It goes behind it in the photo, turns left parallel to the burrito, but behind it. It is at all times outside the burrito. Then, you can see it popping back into view. The burrito is for vapours only, it's purpose is to prevent fuel entering the vent pipe which exits the burrito and then exits the tank at the rear.
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The fuel return does not enter the burrito. It goes behind it in the photo, turns left parallel to the burrito, but behind it. It is at all times outside the burrito. Then, you can see it popping back into view. The burrito is for vapours only, it's purpose is to prevent fuel entering the vent pipe which exits the burrito ant then exits the tank at the rear.
Oh, ahhhaa, I see... I do not see the return line popping back into view but that makes sense, thanks for that! So now back to Laitch's suggestion of fitting a piece of submersible line to the cut-off stub in order to get rid of the cicadas :)
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You can see the end of the fuel return pipe pop back into view, but you have labelled it as a barbed pump breather.
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You can see the end of the fuel return pipe pop back into view, but you have labelled it as a barbed pump breather.
OK, I labeled it so, because that is what it is according to Laitch:
The short barbed pipe adjacent to the burrito collector is a vent pipe attached to the filter basket via a hose. The hose that attaches the two is not a high pressure fuel hose, it is a submersible vent hose.
There is a lot of misunderstanding of what is what, as the design of various components changed over the course of the production and obviously God only knows, what kind of a tank is on my bike manufactured in 1986 (but certainly replaced by the previous owner, as the original one was eaten by a too aggressive paint stripper). The pump assy inside was a hatchet job of a narrow aftermarket pump zip-tied to a deteriorating 53mm rubber insulator and it's filter basket without a hose attached
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I think he is suggesting that the hose directs fuel from the return pipe to the pump to displace any air bubbles from cavitation caused by the pump.
Rbm explains that under his photo too.
Look at reply #4 by BrickMW. See the red line close to the burrito, that is possibly where your pipe has-been cut. Hopefully it has been supported somehow to regain stability. At least it looks stable.
My bike doesn't have that hose either, and it runs fine.
By the way is your air filter good? Any obstructions to the air flow or exhaust?
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I think he is suggesting that the hose directs fuel from the return pipe to the pump to displace any air bubbles from cavitation caused by the pump.
Rbm explains that under his photo too.
Look at reply #4 by BrickMW. See the red line close to the burrito, that is possibly where your pipe has-been cut. Hopefully it has been supported somehow to regain stability. At least it looks stable.
My bike doesn't have that hose either, and it runs fine.
By the way is your air filter good? Any obstructions to the air flow or exhaust?
Air filter is new, replaced in September, some 2000 miles ago. No restrictions, I am aware of, neither is the exhaust leaking.
Upon further investigation it looks like, the barbed pipe on mine is not connected to the burrito either... So I have a favour to ask, would you mind to check inside your tank, if the returning fuel is streaming out of that barbed connection, or some other place?
Thank you!
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My fuel returns through the barbed connection and sprays down onto the bottom of the tank a bit inboard of the fuel level float. It is this way on all three of my Bricks, '94K75S, K75RT, and '91 K100RS. There may be some minor differences in the later models compared to yours, but the operating principles are the same.
There have been two different filter screens for the fuel pump. The earlier version looked like a basket It had a stub on it that a hose from the fuel return barb connected to. I guess that the idea behind the hose is to prevent pump cavitation caused by a dirty screen.
Later models had a larger screen shaped like a sock. I suppose the larger filter area of the new style reduced the risk of cavitation so the hose from the return wasn't needed.
I like having the returned fuel visibly splash in the tank. It's an easy way to confirm that the fuel delivery system is working. As far as noise, the only noise I hear from my tanks is the running of the fuel pump when I am down to 1-2 liters in it. Kind of a final warning that I need to get fuel.
Regarding your fuel efficiency, 29-30 MPG is very low. The lowest I have ever seen on my bikes is 38 MPG. You say your plugs are tan and all the components are working correctly. As far as I know, that only leaves the ECU and your odometer. If the bike is performing properly and the plugs look good I would think the ECU is working properly. That leaves the odometer. I would suggest checking the tripmeter by riding a known distance. A measured run of at least 20 km. My experience is that the odometers are very accurate, but you never know.
Do you warm up the engine before riding off? Are you frequently stuck in traffic? I know from personal experience that can lower fuel mileage by as much as 10% depending on how far you travel.
Another possibility is a slipping clutch. Can you make the engine rpm's increase without increasing the speed, especially in 4th or 5th gear? Dragging brakes can cause reduced fuel efficiency as well. Is the bike easy to push?
You mention MPG. Have you measured your efficiency recently in km/l?
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Hall Sensor was not touched, as a failing one would give me all sorts of driveability problems, wouldn't it?
The suggestion was to look at it, not touch it. A mis-adjusted sensor could affect performance without being a failing sensor—a timing issue. Until weather is suitable and you have the tools and opportunity to finish diagnosing your engine, you'll probably just need be satisfied with what you have.
The fuel seems to be getting to the cylinders regardless of the chop-job done in the tank that might have been done by its previous owners.
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The suggestion was to look at it, not touch it. An mis-adjusted sensor could affect performance without being a failing sensor—a timing issue. Until weather is suitable and you have the tools and opportunity to finish diagnosing your engine, you'll probably just need be satisisfied with what you have.
The fuel seems to be getting to the cylinders regardless of the chop-job done in the tank by its previous owners.
OK, is there a way to check, if the Hall Sensor is in the right place? Or am I asking something that is obvious and described in detail in numerous posts? :)
Fuel is getting where it should, mainly because I replaced that crappy pump and the clogged fuel filter a while back, now there is a proper stream of returning fuel (and hence an army of cicadas inside)
I have taken the plugs out today to check again, they look OK to me:
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I would say that your plugs look very good, maybe even a tiny bit on the lean side. Your fuel/air mixture is pretty good, along with the other operating conditions like cooling, etc.
You mention the army of cicadas. Are you absolutely sure the isolation damper for the pump is installed correctly and the pump is not touching anything in the tank? If the engine is running you should only be able to hear the pump if the tank is almost empty.
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The 2v Bricks have a built in mixture check. With your bike idle set at 1000RPM press the green start button. If the mixture is correct the idle should stay the same or rise slightly if the idle rises significantly it's lean if the RPM's drop or it dies it's too rich. There are a couple of ways to adjust the mixture 1/ The lean drop method instructions on this site 2/ Use an exhaust gas analyser.
Regards Martin.
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Ay Martin, how does it work ay.
I've used your tip on all my bricks, luckily they have all been good. How does pressing the button alter the mixture? Is there a way to understand it, or is it by computer magic?
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When you press the green button it richens the mixture. I've been told that after 711 RPM the computer stops the starter from engaging, I haven't checked it. I do my checks at 1000RPM. Some have alluded that pressing the starter while going can be used as a boost, I did try it and it didn't make any difference. :tinhat2
Regards Martin.
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Thanks, that makes sense.
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Ay Gabe (sorry there's too many syllables in Gabriel)
I can only get to my '92 k100 today. It's way different plus it was made from pieces by the previous owner. The fuel return pipe is welded to the filler area and does a u turn, the fuel lands on the raised centre portion of the tank at the front. There is a mini burrito, smaller than the fuel pump relay. There is a barb on the left, fuel does not exit it. BrickMW's photo shows the barb as the return exit. The barb on the left on my bike is noticeably smaller in diameter than the return pipe so is probably a vent for the old style pump. The diameter of yours might give you a clue.
Since Gryph's also exits on the right, maybe yours hasn't been cut, maybe it had a hose that was roughly removed, bending the pipe, so that it now unfortunately squishes the fuel between the top of the tank and the burrito.
Have you done a compression test? Are all exhaust headers equally hot?
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Is the returning fuel causing the float to tap against the side wall of the tank?
Filter, hose or cables tapping against anything?
If your feeling lucky you would only have to bend it a little, so as to avoid the burrito, well are you?
Maybe bend the float wire too, if its too close to the wall.
Your exhaust may not be leaking, but is it partially blocked, and are there swishing, hissing sounds coming from it?
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My fuel returns through the barbed connection and sprays down onto the bottom of the tank a bit inboard of the fuel level float.
There have been two different filter screens for the fuel pump. The earlier version looked like a basket It had a stub on it that a hose from the fuel return barb connected to. I guess that the idea behind the hose is to prevent pump cavitation caused by a dirty screen.
Regarding your fuel efficiency, 29-30 MPG is very low. The lowest I have ever seen on my bikes is 38 MPG. I would suggest checking the tripmeter by riding a known distance. A measured run of at least 20 km. My experience is that the odometers are very accurate, but you never know.
Do you warm up the engine before riding off? Are you frequently stuck in traffic?
Another possibility is a slipping clutch. Can you make the engine rpm's increase without increasing the speed, especially in 4th or 5th gear? Dragging brakes can cause reduced fuel efficiency as well. Is the bike easy to push?
You mention MPG. Have you measured your efficiency recently in km/l?
You mention the army of cicadas. Are you absolutely sure the isolation damper for the pump is installed correctly and the pump is not touching anything in the tank
Gryphon, I somehow completely missed your first response, sorry. As there is no fuel coming out of the barbed end on mine, we can safely say, the return line has been cut and the remaining stub cut off up to the barbed end, as I can not find the missing piece by feeling around the collector. No biggie as long as I know from Daveson's reply, that line never enters the burrito. I will get a length of submersible line connected to the cut off end, even though there will be no barb to retain it, so it might slip off eventually. The army of cicadas is the noise, splashing petrol makes first on the edge of the burrito then hitting the wall of the tank. The pump starts it's noisy operation, when I am really low on petrol, just like on yours, I guess the empty tank becoming a resonance chamber.
Fuel consumption wise, I have converted l/100km to MPG, I should have gone to fuelly straight, as I see, I have made a calculation error - please see my profile at http://www.fuelly.com/motorcycle/bmw/k75/1986/szabgab/840106/fuelchart Disregard the first fuel up, as that was, when I have gotten the bike and it was partially filled by the PO, so that reading is better, than anything else measured by me. Also there was a really bad 8.2l/100km consumption in December, but I must have been so shocked, I forgot to log it :) I do a lot of city rides, basically the bike lives in the metro area rarely venturing further, than let's say 20 miles, I do warm up the bike before take off and being inpatient I chose routes, where I do not have to be held up by the cagers too much.
Clutch is not slipping fortunately, however I did have problems with my brakes, especially the rear one dragging slightly. That is an odd one, as the bike is very easy to push since servicing all three calipers and master cylinders, but somehow the rear rotor still gets hot to the touch after rides.
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As there is no fuel coming out of the barbed end on mine, we can safely say, the return line has been cut and the remaining stub cut off up to the barbed end, as I can not find the missing piece by feeling around the collector. The pump starts it's noisy operation, when I am really low on petrol, just like on yours, I guess the empty tank becoming a resonance chamber.
I believe we can safely say none of that. I believe you have a later model tank that is exhibiting classic noisy pump symptoms caused by fuel not being returned to the most effective location for uptake when the fuel volume is low. I alluded to this and its remedy in an earlier post. Fuel is coming from the correct pipe in the correct location within your moto's tank. I've attached to this post a service bulletin that describes this condition. In the service bulletin's low-quality illustrations, notice the size and location of the pipe into which the prying tool is inserted. A ghostly burrito appears to the right of the pipe. The pipe looks to me like the one dumping fuel in your first video. The pipe is being carefully pried away from the burrito to allow room for the hose and its clamp. Use of a high-quality fuel injection hose clamp to attach the hose to the pipe should fasten it securely to the pipe. This is something you can do.
I do a lot of city rides, basically the bike lives in the metro area rarely venturing further, than let's say 20 miles, I do warm up the bike before take off and being inpatient I chose routes, where I do not have to be held up by the cagers too much.
It's unreasonable to expect low fuel consumption if the bulk of your riding is short haul in cold weather on a moto that has not been fully tuned. Short-duration cold weather riding is hard on engines even with a warmup. The warmup is mainly effecting water temperature. Lubrication needs more time in circulation to perform optimally and increase engine efficiency. Once weather warms and you've completed your engine maintenance, fuel consumption will probably lessen. The moto needs distance riding to get it in shape. Use your scooter for commuting. Put skull decals on it to give it street cred, if you haven't done that already. :giggles
A 10-year old Prius up here in the mountains drops from 45–55mpg in mild weather down to 38mpg in winter.
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The coolant temp sensor was checked as a first thing back in September at the computer, as recommended by you and the others. I can not check it now, as it is still a tad cold outside to get the bike boiling over (top daytime temp is 10-15C).
You could check it right now because it doesn't matter how cold it is outside. The coolant temperature sensor is removed, immersed in boiling water, connected to the leads of a multi-meter, then as it cools, the resistance values are compared with widely-accepted specifications. Admittedly, parts need to be removed to access the sensor and that task certainly could be inconvenient for a self-described impatient man on the go.
The plugs look good though, so the task seems optional right now. :yippee:
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The 2v Bricks have a built in mixture check. With your bike idle set at 1000RPM press the green start button. If the mixture is correct the idle should stay the same or rise slightly if the idle rises significantly it's lean if the RPM's drop or it dies it's too rich. There are a couple of ways to adjust the mixture 1/ The lean drop method instructions on this site 2/ Use an exhaust gas analyser.
Regards Martin.
HI Martin, I have tried that a few times before, pressing the starter button does absolutely nothing, so I guess my mixture is OK.
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Is the returning fuel causing the float to tap against the side wall of the tank?
Filter, hose or cables tapping against anything?
If your feeling lucky you would only have to bend it a little, so as to avoid the burrito, well are you?
Maybe bend the float wire too, if its too close to the wall.
Your exhaust may not be leaking, but is it partially blocked, and are there swishing, hissing sounds coming from it?
Dave, the hissing sound is very obviously coming from the tank if you are next to the bike. It is (was) the fuel stream hitting the burrito full blast and subsequently the wall of the tank
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The coolant temperature sensor is removed, immersed in boiling water, connected to the leads of a multi-meter... Admittedly, parts need to be removed to access the sensor and that task certainly could be inconvenient for a self-described impatient man on the go.
The plugs look good though, so the task seems optional right now. :yippee:
:) For some reason I am impatient with city traffic only when riding a bike (although seeing all them others race off from red lights and so on is not my world), I drive a car like a grandpa on sedatives.
Would this extensive test be necessary, if the values measured at the computer are well within specs?
What about the HES? Is there an easy way to tell, if timing is correct?
Thanks!
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Would this extensive test be necessary, if the values measured at the computer are well within specs?
What about the HES? Is there an easy way to tell, if timing is correct?
You already asserted the coolant temperature sensor values at the computer were in spec; I already stated the more complex test was optional.
Wait a minute! You've already set the valve clearances. As far as determining an easy way to tell if timing is correct, describe what seems easy to you and what seems difficult. That will establish your personal baseline.
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Timing is fairly easy to check. Remove the "T" shaped cover from the front of the engine. Behind it you will find the plate the HES are mounted on. The plate and the valve chain cover are machined to provide a cutout inspection hole where you can see the timing mark in the unlikely event you can get your head and a timing light in there. The opening is about 13mm wide and at the 3 o'clock position on the HES plate.
The good news here is that when the edges of the cutout in the two parts are aligned, the timing will be at factory specifications. This is the way the timing is set according to the factory manual I have. All my bikes are timed that way and they run well and get 45-48 MPG.
Do you have a temperature gauge? How long does it take to get to normal temperature? My bikes can take as long as 4-5 miles in cold weather(0-10C). If you are doing city trips there is a good chance as much as 80% of the trip is being done with the cold engine enriched mixture.
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I was wondering if there was a hissing (esp. under revs) from your exhaust as a sign of a blockage, but after seeing your fuel economy I'm thinking there is nothing wrong with your bike (except return line - burrito syndrome) it's good for a high performance engine in a harsh environment.
I'm thinking your fuel economy should not be improved by the previous owners fuel since the fuel you put in should be measured against the distance that has been travelled, not the distance that will be.
Maybe clean the speedo sensor. In fifth gear the speedo and rev needles should be parallel at all times.
Do you fill your bike while on the centrestand? I fill mine on the side stand, to the lowest point of the filler neck, so the burrito is above the fuel line. Also, if full on the centrestand, I wonder how much the fuel expands as it heats up, because that would mean adios amigo out burrito.
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As an attempt to thwart continuing misunderstanding of later model Classic K moto fuel tank vent and fuel pipe assemblies, and to help clarify for myself what is going on within these critters, I have modified one of the useful images posted by rbm way-back-when in this thread. Edit suggestions are welcomed.
(http://www.motobrick.com/gallery/1/1601-220219172759.png)
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Well done Laitch, rbm. Thanks.
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Timing is fairly easy to check. Remove the "T" shaped cover from the front of the engine. Behind it you will find the plate the HES are mounted on. The plate and the valve chain cover are machined to provide a cutout inspection hole where you can see the timing mark in the unlikely event you can get your head and a timing light in there. The opening is about 13mm wide and at the 3 o'clock position on the HES plate.
The good news here is that when the edges of the cutout in the two parts are aligned, the timing will be at factory specifications. This is the way the timing is set according to the factory manual I have. All my bikes are timed that way and they run well and get 45-48 MPG.
Do you have a temperature gauge? How long does it take to get to normal temperature? My bikes can take as long as 4-5 miles in cold weather(0-10C). If you are doing city trips there is a good chance as much as 80% of the trip is being done with the cold engine enriched mixture.
Oh, that sounds simple enough. Once my boy is in kindergarten tomorrow I will dig in to check, what's what, if I am unsure, I will post some pictures. 45-48MPG is dream territory for me, I am currently on 32MPG according to fuelly, but Laitch and you are correct, a cold engine on short trips will be heavy on gas. However I have taken the bike for a spin of 150-200 miles back in October in balmy 22C, and my fuel consumption did not lower significantly, so in the springtime I will carry on fault finding.
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It seems your getting 6 to 7 litres per hundred km. I'm thinking that's 43 MPG (36 US)
That's not bad for a thirty year old bike.
Some say you should warm up your bike, some say you shouldn't. I'm thinking one minute is plenty but takes me two to shut the garage door and gear up. In that time the bike may have pumped about 100 litres of oil, surprisingly.
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It seems your getting 6 to 7 litres per hundred km. I'm thinking that's 43 MPG (36 US)
That's not bad for a thirty year old bike.
Some say you should warm up your bike, some say you shouldn't. I'm thinking one minute is plenty but takes me two to shut the garage door and gear up. In that time the bike may have pumped about 100 litres of oil, surprisingly.
Dave, that probably would be the case, if everybody else would be getting similar stats. All my other bikes - calculating in my weight (70kg), my ridding habits and after some TLC were getting consumption in the lower half of the average and I was kind of expecting that with this bike too. I know, riding a 750cc touring bike in the metro is less than ideal and I knew, I will have to pay more for fuel than I would have had with a 125cc modern scooter. However the absolute best, I have gotten with this was 40MPG, that is way below average as the median on fuelly looks to be more like 42-45MPG. Warming up is another hotly debated topic, I do not think, one harms the bike, if it gets nearer operating temperature before loading it, I give it two minutes or so too... Anyway, once I really do get everything done to the bike that is to be done and the weather clevers up I will see, how things change...
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As an attempt to thwart continuing misunderstanding of later model Classic K moto fuel tank vent and fuel pipe assemblies, and to help clarify for myself what is going on within these critters, I have modified one of the useful images posted by rbm way-back-when in this thread. Edit suggestions are welcomed.
(http://www.motobrick.com/gallery/1/1601-220219172759.png)
Laitch this is brill!
I have done, what was suggested, and bent the pipe yesterday. Carefully was a no-go as there is no room to get in a pipe wrench or proper tools, also one can do anything only by feeling around, so at the end I managed to get the end of the pipe somewhat squashed. It is not restricting fuel flow, so I left it like that and attached a fuel pump breather hose, as that was the only submersible thing, the BMW place had in stock. Being impatient, I bought a metre of it. Got it on the pipe as far as I could spraying the tube with brake cleaner and pushing it on, whilst wet. It is steady, time will only tell, if it is steady enough in the long run. Routed it to the pump and through the hole, that is there for the breather hose specifically but did not attach it to the pump, as I do not have the filter basket with the nipple on. The secret waterfall, or the league of critters immediately left my tank, all I can hear is the quiet high pitched noise of the pump.
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There are a few quick easy tests you can do. Are the needles parallel in fifth gear? Mine are, we have metric here but I don't think that matters. You might have a non original final drive. Is the speedo accurate?
It seems to me roughly say 6.5lt/100km, looking at that metric graph, I googled that to 43MPG, maybe my maths is wrong or something.
The final drive ratio is usually stamped on the top, near the swing arm.
I'm thinking, be sure your fuel economy is bad before looking for the cause.
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I cannot think of any reasons why your plugs look so good with the fuel efficiency you say you are getting. They should be black and sooty with the amount of fuel you say you are using, certainly not as clean as yours look.
Are you absolutely sure your trip meter is running properly? It is driven by a small electric motor that is speed controlled by some electronics and the rear wheel sensor. I think it is possible that it could be running slow because of drag in the gearing and not registering distance accurately.
I would suggest taking a ride on a motorway with km markers and checking your readings against them. a minimum 25-30 km trip should tell you if everything is accurate.
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I'll use 5L/100km when on longer out of town rides at 80 to 120 kph. In town is another story. My workshop is 1km away and my clients, groceries, banking, beer, etc are all within a 5km radius. I'll use 7.5L/100km in town.
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Guys, I created a new thread in Classic Motobricks, as not to completely hijack this one. I have replied to your comments there and would migrate everything from Laitch's brilliant picture onward, but I do not have the rights :)