Author Topic: k75 backfires, stalls, and bucks like a mf  (Read 1886 times)

Offline Laitch

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Re: k75 backfires, stalls, and bucks like a mf
« Reply #50 on: September 02, 2019, 05:42:03 PM »
  • Along the Ridley in Vermont.
  • 1995 K75 72,000 miles
I wept because I had no radials until I met a man who had no splines.
http://www.motobrick.com/index.php/topic,296.msg53303.html#msg53303
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Offline evanwellsk75

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Re: k75 backfires, stalls, and bucks like a mf
« Reply #51 on: September 04, 2019, 03:23:16 PM »
update, its backfiring like crazy above 4k rpms
  • Denver CO
  • 1986 K75

Offline Martin

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Re: k75 backfires, stalls, and bucks like a mf
« Reply #52 on: September 04, 2019, 05:50:19 PM »
When you replaced the return fuel hose from the FPR to the tank did you replace it with a OEM one with the preformed bends? If not depending on the quality of the hose used and the temperatures encountered it is possible for the hose to collapse where it goes into the tank. The collapse can be hard to detect even when sliding the tank back to check. As you slide the tank back the kink in the hose can rectify itself. A collapsed hose will cause symptoms similar to what you are encountering.
Regards Martin.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.
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Offline volador

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Re: k75 backfires, stalls, and bucks like a mf
« Reply #53 on: September 04, 2019, 05:59:05 PM »
 Nice! Terrorizing the pristine Utah country side with a backfiring Brick. :laughing4-giggles:

You borrow a hair dryer from any motohoe and try that HES test?

You may also have too little throttle cable “play” which may be holding the butterflies slightly off idle, keeping the throttle position switch actuated. Check for a audible “click” at the injector area as you slowly ease off the twistgrip to idle. If the throttle position switch is incorrectly adjusted or the throttle cable too tight, you won’t hear the “click”, and the engine will receive fuel as you decelerate, causing backfiring.

Remove the plug for the throttle position switch.
Go for a ride. Any change?
  • NYC
  • 1991 K100RS 1993 K75S ABS
5 BOROUGHS SISYPHEAN SOCIETY "When Life Throws You A Curve... Lean Into It"
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Offline evanwellsk75

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Re: k75 backfires, stalls, and bucks like a mf
« Reply #54 on: September 04, 2019, 08:13:32 PM »
When you replaced the return fuel hose from the FPR to the tank did you replace it with a OEM one with the preformed bends?



please exuse my ignorance here, but what does FPR stand for? and no none were oem, just standard fuel injection hoses.
  • Denver CO
  • 1986 K75

Offline evanwellsk75

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Re: k75 backfires, stalls, and bucks like a mf
« Reply #55 on: September 04, 2019, 08:18:45 PM »
Havent done the HES test yet, could be throttle position? I had to take the throttle handle off do replace a bad brake piston about 2 weeks ago, so the cable might have gotten jammed or something- would that make sense though?

Also, went for a ride today in utah to grab a circle clamp to throw between my airbox and throttle body (it was straight up gone and they were disconnected ??? thought that might be the source) and the bike was hard to start when i got out of the parts shop. got to the joint im staying at and put the bike in the garage for lunch, came back 1 or 1:30 hours later and the engine was scorching hot to the touch. Ever experienced something like that?
  • Denver CO
  • 1986 K75

Offline evanwellsk75

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Re: k75 backfires, stalls, and bucks like a mf
« Reply #56 on: September 04, 2019, 08:20:13 PM »
never mind got the click alright
  • Denver CO
  • 1986 K75

Offline evanwellsk75

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Re: k75 backfires, stalls, and bucks like a mf
« Reply #57 on: September 04, 2019, 08:50:52 PM »
Well so just revved the bitch up for about 10, then let it idle and ran a hairdryer over it for another ten. So i guess when it comes to evans bike you can go so far to say HE'S gooooooooooooouuuud
  • Denver CO
  • 1986 K75

Offline volador

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Re: k75 backfires, stalls, and bucks like a mf
« Reply #58 on: September 04, 2019, 08:53:28 PM »
You take the "T" shaped cover off and heat the HES ?

FPR - Fuel Pressure Regulator

The top barb on the FPR has hose connects to the underside fuel tank return port/tubing stub
  • NYC
  • 1991 K100RS 1993 K75S ABS
5 BOROUGHS SISYPHEAN SOCIETY "When Life Throws You A Curve... Lean Into It"

Offline Laitch

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Re: k75 backfires, stalls, and bucks like a mf
« Reply #59 on: September 04, 2019, 11:00:22 PM »
. . . went for a ride today in utah to grab a circle clamp to throw between my airbox and throttle body (it was straight up gone and they were disconnected . . . 1 or 1:30 hours later and the engine was scorching hot to the touch.
If the throttle body intake bushings weren't attached to the air box, then un-metered air was being taken into the throttle bodies leaning the mixture in the combustion chambers. That was likely to contribute to chronic backfiring and the poor performance of this derelict from the get-go.

Hot engine? How old is the coolant and what's its level in the reservoir?
  • Along the Ridley in Vermont.
  • 1995 K75 72,000 miles
I wept because I had no radials until I met a man who had no splines.
http://www.motobrick.com/index.php/topic,296.msg53303.html#msg53303

Offline volador

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Re: k75 backfires, stalls, and bucks like a mf
« Reply #60 on: September 04, 2019, 11:42:43 PM »
Well so just revved the bitch up for about 10, then let it idle and ran a hairdryer over it for another ten. So i guess when it comes to evans bike you can go so far to say HE'S gooooooooooooouuuud

Ayy, hit'in the good stuff in Utah
  • NYC
  • 1991 K100RS 1993 K75S ABS
5 BOROUGHS SISYPHEAN SOCIETY "When Life Throws You A Curve... Lean Into It"
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Offline Martin

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Re: k75 backfires, stalls, and bucks like a mf
« Reply #61 on: September 04, 2019, 11:44:19 PM »
FPR stands for fuel pressure regulator  it is fitted between the fuel rail return line and the tank. I've had previous trouble with the line collapsing where it goes back into the tank. The Gates brand line had been substituted by a cheaper type by our local auto supply shop. Due to the inferior quality of the new hose it was collapsing on the bend, the heat in QLD summer and slow traffic were also a contributing factor. The problem was solved by fitting a better grade hose along with a Unicoil on the bend, I also added 13mm by 10mm thick foam insulation.
Regards Martin.

* Unicoil 1.jpg (4.78 kB . 140x105 - viewed 61 times)
* Hose insulation.jpg (13.99 kB . 190x190 - viewed 63 times)
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.
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Offline evanwellsk75

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Re: k75 backfires, stalls, and bucks like a mf
« Reply #62 on: September 05, 2019, 02:33:11 AM »
Oh yup gotcha all sorry for the disconnect, yup replaced the fpr when I refurbished the bike and replaced the line. Could be that the line collasped however, will take a second look at in it the morn.
Also yup took off the hes cover and heated it, the t shaped one.
  • Denver CO
  • 1986 K75

Offline evanwellsk75

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Re: k75 backfires, stalls, and bucks like a mf
« Reply #63 on: September 05, 2019, 02:36:08 AM »
Well so Laitch, i dont quite know what you mean by bushings there are two large hoses that connect the two and they have a circle clamp on the outside and a medium sized metal piece on the inside. The circle clamp was missing and the hoses were loose.

As for coolant age no idea but levels have looked good since i left denver
  • Denver CO
  • 1986 K75

Offline Laitch

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Re: k75 backfires, stalls, and bucks like a mf
« Reply #64 on: September 05, 2019, 10:50:16 AM »
Well so Laitch, i dont quite know what you mean by bushings there are two large hoses that connect the two and they have a circle clamp on the outside and a medium sized metal piece on the inside. The circle clamp was missing and the hoses were loose.

As for coolant age no idea but levels have looked good since i left denver
Well evan, bushings are the BMW term for what you seem to be calling hoses. Hoses are what I call flexible tubes long enough for a K75 owner to flog himself as punishment for not getting acquainted with a parts fiche like this one or not knowing the condition of essential fluids in his moto's engine. :-)

  • Along the Ridley in Vermont.
  • 1995 K75 72,000 miles
I wept because I had no radials until I met a man who had no splines.
http://www.motobrick.com/index.php/topic,296.msg53303.html#msg53303

Offline evanwellsk75

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Re: k75 backfires, stalls, and bucks like a mf
« Reply #65 on: September 05, 2019, 02:59:23 PM »
Thanks for the help there laitch! Saying the same thing over and over then being an asshole about it really does improve the all around community! God what would I do without you? Maybe I would have never reconnected my intake hoses like I did yesterday. What if I had called them vents? Or tubes? Literally any other descriptor for an oddly named piece seems to be too hard for you though, so god I am so sorry since I have done such a dishonor to you by asking for advice the wrong way. How ever can I make it up????

get off the thread, your not helpful.
  • Denver CO
  • 1986 K75

Offline Soggz

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  • 2 wheels are better than 4,but 4 wheels,2 bikes...
Re: k75 backfires, stalls, and bucks like a mf
« Reply #66 on: September 05, 2019, 03:22:13 PM »
Thanks for the help there laitch! Saying the same thing over and over then being an asshole about it really does improve the all around community! God what would I do without you? Maybe I would have never reconnected my intake hoses like I did yesterday. What if I had called them vents? Or tubes? Literally any other descriptor for an oddly named piece seems to be too hard for you though, so god I am so sorry since I have done such a dishonor to you by asking for advice the wrong way. How ever can I make it up????

get off the thread, your not helpful.
lol.
Nice.
I had a slight air leak difficulties with my rear one of these,the top inner side of it looked ‘chipped’, maybe forced on. I just cleaned everything with a mild degreased, then spread black silicone sealer around the inside top, then reassembled it all, then left overnight to cure. That was just under a thousands miles ago, with no problems.
Admittedly, it had been off of the road for a number of years, so I had to do other things to it,too.
But these bike seem to be one of many parts, and to me, a new learning curve, on otherwise,quite a simple engine once you get to the extra ‘elektrickery’, it has.

Hope this helps.
  • Down in Selwood Forest
  • 1986 K75C, 1982 Honda CX500EC Eurostreetbrat
One More Of These,One Less Of Those...

Offline volador

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Re: k75 backfires, stalls, and bucks like a mf
« Reply #67 on: September 05, 2019, 03:40:02 PM »
Woooww Dude, chill out. The man is helping you!

Smear some silicone/grease/saliva inside the intake bushings/hoses/stubs/vents/tubes/whatever  if/ when you are reassembling
Any change in the moto performance?
  • NYC
  • 1991 K100RS 1993 K75S ABS
5 BOROUGHS SISYPHEAN SOCIETY "When Life Throws You A Curve... Lean Into It"

Offline Laitch

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Re: k75 backfires, stalls, and bucks like a mf
« Reply #68 on: September 05, 2019, 04:02:32 PM »
Thanks for the help there laitch!
The pleasure has been all mine, evan! Anytime.
  • Along the Ridley in Vermont.
  • 1995 K75 72,000 miles
I wept because I had no radials until I met a man who had no splines.
http://www.motobrick.com/index.php/topic,296.msg53303.html#msg53303

Offline evanwellsk75

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Re: k75 backfires, stalls, and bucks like a mf
« Reply #69 on: September 05, 2019, 04:28:20 PM »
Okay my apologies to the forum. I have zero patience for public shaming or condescension.

Now I popped my airbox off and maybe found the cause for the mix up, I dont have a bushing in there. I also went into my book and found no mention of a bushing being there. So maybe the bushing thing is a function of later models, since this is a 86. I no longer think this could be the cause of my problem, since the bike was running great before this clusterfuck. Here are some pictures of what Im looking at.

Also would like to point out that the hose that I have been referring to as a hose, the book refers to as a air intake hose. 


http://www.motobrick.com/index.php?action=gallery;su=user;cat=147;u=6448

http://www.motobrick.com/gallery/videos/1_12_01_19_6_45_32.gif


  • Denver CO
  • 1986 K75

Offline Laitch

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Re: k75 backfires, stalls, and bucks like a mf
« Reply #70 on: September 05, 2019, 04:49:51 PM »
That elbow is a pathway to the airflow meter. The meter signals air volume to the Jetronic fuel injection control unit which adjusts the fuel mixture accordingly. If air bypasses that meter the engine will run unpredictably and rough. Be certain the electrical connector is attached snugly.

Bushings referred to the rubber connectors attaching the throttle bodies to the plenum, the box above them.

To post your photos into your reply, go to the bottom of each photo's page in your gallery. The URL information of the photo is in a narrow window. Copy all the information then paste it into the reply box wherever you want the photo to appear.
  • Along the Ridley in Vermont.
  • 1995 K75 72,000 miles
I wept because I had no radials until I met a man who had no splines.
http://www.motobrick.com/index.php/topic,296.msg53303.html#msg53303

Offline evanwellsk75

  • Motobrick Curious
  • Posts: 37
Re: k75 backfires, stalls, and bucks like a mf
« Reply #71 on: September 05, 2019, 05:41:27 PM »
Solved.

I used the propane test to identify that one of by intake tubes under the butterfly assembly had gone bad, item number 3 in the diagram.



As for the propane testing that I did i found the info on how to do that from a thread called k1100 intake rehab

Heres the link
http://www.motobrick.com/index.php/topic,624.msg1572.html#msg1572

Again the book I have refers to the piece in the intake manifold as a tube not bushing. Though thank you for the help.
  • Denver CO
  • 1986 K75
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Offline Laitch

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Re: k75 backfires, stalls, and bucks like a mf
« Reply #72 on: September 06, 2019, 01:11:30 AM »
Again the book I have refers to the piece in the intake manifold as a tube not bushing. Though thank you for the help.
As was indicated earlier, bushings is BMW's term. It isn't necessarily a widely used term but it's they one use in the order forms accompanying the diagrams for ordering parts from their dealesr. Sometimes it's useful to know the arcane terms BMW uses when mounting a search on the Internet for replacement parts.

I guess we're both repeating ourselves. :-)
  • Along the Ridley in Vermont.
  • 1995 K75 72,000 miles
I wept because I had no radials until I met a man who had no splines.
http://www.motobrick.com/index.php/topic,296.msg53303.html#msg53303

Offline volador

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  • Posts: 171
  • NEEDS MORE CHROME
Re: k75 backfires, stalls, and bucks like a mf
« Reply #73 on: September 06, 2019, 02:11:46 AM »
As was indicated earlier, bushings is BMW's term. It isn't necessarily a widely used term but it's they one use in the order forms accompanying the diagrams for ordering parts from their dealesr. Sometimes it's useful to know the arcane terms BMW uses when mounting a search on the Internet for replacement parts.

I guess we're both repeating ourselves. :-)

Compulsive repetitive disorder, this thread needs some therapy. I'd be happy to recommend someone.:laughing4-giggles:
  • NYC
  • 1991 K100RS 1993 K75S ABS
5 BOROUGHS SISYPHEAN SOCIETY "When Life Throws You A Curve... Lean Into It"

Offline Laitch

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Re: k75 backfires, stalls, and bucks like a mf
« Reply #74 on: September 06, 2019, 02:27:53 AM »
Compulsive repetitive disorder, this thread needs some therapy. I'd be happy to recommend someone. :laughing4-giggles:
The Sisyphean Society must have quite the database of therapists. Ping me.
  • Along the Ridley in Vermont.
  • 1995 K75 72,000 miles
I wept because I had no radials until I met a man who had no splines.
http://www.motobrick.com/index.php/topic,296.msg53303.html#msg53303

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