Author Topic: Fuel from exhaust - no start whackness.  (Read 843 times)

Offline DJEwen

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Fuel from exhaust - no start whackness.
« on: August 01, 2019, 12:47:57 PM »
Hello,

Iíve just gone out to take my Motobrick for a ride and she didnít start, after a few attempts I could smell fuel, I then realised fuel is steadily dripping from the exhaust when start button is pressed.

I went to grab my multimeter and the trouble starting guide, dropped the multimeter and smashed the screen... Iíve ordered a new one.

In the meantime I pulled the vacuum hose that connects between throttle body #4 and the bottom of the fuel pressure regulator to check for a presence of fuel, it was dry so I suspect there isnít a diagram leak in the FPR.

Is there anything else I can do in the interim without a multi meter?
  • Scotland
  • 1985 K100 'Revive', 1987 K100 LT

Offline Laitch

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Re: Fuel from exhaust - no start whackness.
« Reply #1 on: August 01, 2019, 01:21:49 PM »
Is there anything else I can do in the interim without a multi meter?
Disconnect, reconnect the electronic fuel injector control unit plug; remove the fuel pump fuse and crank to dry off the plugs or remove them, dry them lovingly and individually, replace them then try starting with no throttle.
  • Along the Ridley in Vermont.
  • 1995 K75T 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 DJEwen

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Re: Fuel from exhaust - no start whackness.
« Reply #2 on: August 01, 2019, 02:09:25 PM »
Disconnect, reconnect the electronic fuel injector control unit plug; remove the fuel pump fuse and crank to dry off the plugs or remove them, dry them lovingly and individually, replace them then try starting with no throttle.

Done as you said, no change. The plugs werenít overly wet but I pulled them all, cleaned and gapped them. I cranked the bike with the plugs out and the pump and injectors disconnected to clear the inlets and it looked like #2 and #4 werenít sparking (difficult to see as Iím in my own) so potentially a cool issue? Why are the injectors remaining open and pouring fuel in? Video of fuel leak below.



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  • 1985 K100 'Revive', 1987 K100 LT

Offline Laitch

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Re: Fuel from exhaust - no start whackness.
« Reply #3 on: August 01, 2019, 02:53:41 PM »
Why are the injectors remaining open and pouring fuel in? Video of fuel leak below.
I went to grab my multimeter and the trouble starting guide, ...
Because one or more is stuck open and there is enough fuel pressure to force fuel through the aperture.

Consider not using that trouble starting guide. It's starting too much troubleóreaching out and affecting coordination and gravity.   :laughing4-giggles:
  • Along the Ridley in Vermont.
  • 1995 K75T 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 Laitch

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Re: Fuel from exhaust - no start whackness.
« Reply #4 on: August 01, 2019, 03:02:10 PM »
it looked like #2 and #4 werenít sparking (difficult to see as Iím in my own)
If you have a timing light, ground it, put the inductive clamp around each suspected plug's wire, crank the starer and see if it lights.
  • Along the Ridley in Vermont.
  • 1995 K75T 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 Martin

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Re: Fuel from exhaust - no start whackness.
« Reply #5 on: August 01, 2019, 03:55:55 PM »
Over fuelling can also be caused by a faulty temperature sensor or a bad connection. Try starting with the fuel pump fuse #6 marked Krafftstoppe temoved. It should start on the residual fuel left in the combustion chamber, as the engine starts to die ram the fuse back in. A bit of manipulation of the throttle is required. It can be done with one person but two is better.
Regards Martin.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline Soggz

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Re: Fuel from exhaust - no start whackness.
« Reply #6 on: August 05, 2019, 06:28:23 AM »
I had this problem. A new temp sender fixed it.
  • Down in Selwood Forest
  • 1986 K75C, 1982 Honda CX500EC Eurostreetbrat
One More Of These,One Less Of Those...

Offline Gr-Racing

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Re: Fuel from exhaust - no start whackness.
« Reply #7 on: August 05, 2019, 12:35:12 PM »
had the same problem and like other said, new temp sensor was my fix
  • GA
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Offline DJEwen

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Re: Fuel from exhaust - no start whackness.
« Reply #8 on: August 05, 2019, 02:56:27 PM »
Thanks for the input, everyone. Is there a way of testing the switch before I rip it out and replace it?
  • Scotland
  • 1985 K100 'Revive', 1987 K100 LT

Offline Laitch

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Re: Fuel from exhaust - no start whackness.
« Reply #9 on: August 05, 2019, 03:39:07 PM »
Thanks for the input, everyone. Is there a way of testing the switch before I rip it out and replace it?
You'll need a multimeter. Go to this post the open the document in the link at the bottom of the post. Three-quarters of the way through it you'll find an explanation of how to test various circuits on the L-Jetronic plug. There is an illustration of the plug with the circuits labeled. You'll be checking Pin #10óthe coolant temperature sensoróto see how its values correspond with those on the table in that section.
  • Along the Ridley in Vermont.
  • 1995 K75T 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 Soggz

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Re: Fuel from exhaust - no start whackness.
« Reply #10 on: August 05, 2019, 04:19:55 PM »
Or just replace it.
  • Down in Selwood Forest
  • 1986 K75C, 1982 Honda CX500EC Eurostreetbrat
One More Of These,One Less Of Those...

Offline DJEwen

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Re: Fuel from exhaust - no start whackness.
« Reply #11 on: August 05, 2019, 05:09:41 PM »
You'll need a multimeter. Go to this post the open the document in the link at the bottom of the post. Three-quarters of the way through it you'll find an explanation of how to test various circuits on the L-Jetronic plug. There is an illustration of the plug with the circuits labeled. You'll be checking Pin #10óthe coolant temperature sensoróto see how its values correspond with those on the table in that section.

Thanks, Laitch. My new multimeter should arrive tomorrow.

Or just replace it.

Iíve ordered one so itís getting replaced, but I still want to know for myself that this was the only issue.
  • Scotland
  • 1985 K100 'Revive', 1987 K100 LT

Offline Soggz

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Re: Fuel from exhaust - no start whackness.
« Reply #12 on: August 06, 2019, 02:13:30 AM »
Thanks, Laitch. My new multimeter should arrive tomorrow.

Iíve ordered one so itís getting replaced, but I still want to know for myself that this was the only issue.
with those symptoms, and the advice from the good people on here, thereís not much else to go wrong. If the new one dosnt work, get the injectors professionally cleaned. It cost me £50.00 over here.
  • Down in Selwood Forest
  • 1986 K75C, 1982 Honda CX500EC Eurostreetbrat
One More Of These,One Less Of Those...

Offline DJEwen

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Re: Fuel from exhaust - no start whackness.
« Reply #13 on: August 06, 2019, 03:57:52 AM »
with those symptoms, and the advice from the good people on here, thereís not much else to go wrong. If the new one dosnt work, get the injectors professionally cleaned. It cost me £50.00 over here.

I agree but what Iíve learned with this bike is that thereís always something new going on. Iíll take pleasure completing the test, at least Iíll know how itís done point forward. Every day is a school day.

Thatís not a bad price, I was looking at replacing them altogether with 4 hole ones but may go down the cleaning route. I have 4 spare so can send them off.
  • Scotland
  • 1985 K100 'Revive', 1987 K100 LT

Offline Soggz

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Re: Fuel from exhaust - no start whackness.
« Reply #14 on: August 06, 2019, 07:30:19 AM »
I agree but what Iíve learned with this bike is that thereís always something new going on. Iíll take pleasure completing the test, at least Iíll know how itís done point forward. Every day is a school day.

Thatís not a bad price, I was looking at replacing them altogether with 4 hole ones but may go down the cleaning route. I have 4 spare so can send them off.
tbh, if the injectors are working ok, thereís no need to replace them, from what Iíve read. They either work, or they donít, apparently. 4 hole ones donít make a lot of difference. People think they do, but they are new with clean parts. Mine are old, but have been cleaned and work great. Save your money, and replace some of the crap bmw nuts and bolts and electrical connections, instead!
  • Down in Selwood Forest
  • 1986 K75C, 1982 Honda CX500EC Eurostreetbrat
One More Of These,One Less Of Those...

Offline DJEwen

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Re: Fuel from exhaust - no start whackness.
« Reply #15 on: August 06, 2019, 02:45:27 PM »
tbh, if the injectors are working ok, thereís no need to replace them, from what Iíve read. They either work, or they donít, apparently. 4 hole ones donít make a lot of difference. People think they do, but they are new with clean parts. Mine are old, but have been cleaned and work great. Save your money, and replace some of the crap bmw nuts and bolts and electrical connections, instead!

Youíre not the first to mention the non improvement in the 4 hole ones, Iíll give them a miss and get a set cleaned.

Anyway, when I built the bike it was a piece of cake to remove the original temperature sensor as I had the stand pipe off the block and everything stripped down. Different story tonight, Iím not sure if thereís a massively expensive one time use BMW tool for doing this but the design is shit. No space for a spanner, too long a plug for a normal socket, no space for a long reach, no space for purchase with pipe grips etc. I ended up hack sawing the plug off then removing with a standard socket. New temp sender is en route.



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  • 1985 K100 'Revive', 1987 K100 LT

Offline Martin

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Re: Fuel from exhaust - no start whackness.
« Reply #16 on: August 06, 2019, 03:29:52 PM »
The only confirmed difference is increased fuel consumption and a larger chance of them blocking. I am yet to see a dyno comparison between 1 hole versus 4 hole, no company selling the 4 hole ones have posted a dyno report to my knowledge. I would love to see one and wouldn't mind being proved wrong. The difference often quoted is I felt an increase in performance when I fitted the 4 hole injectors over my dirty 1 hole injectors. While on a mission to cure my 75 of occasional backfiring on over run, I built my own cleaner and test rig. Once cleaned and flow checked they proved to be the final piece in the backfiring puzzle. A by product proved to be an increase in seat of pants performance.
Regards Martin.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline The Mighty Gryphon

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Re: Fuel from exhaust - no start whackness.
« Reply #17 on: August 06, 2019, 05:41:47 PM »
Just buy a couple battles of Techron and put half a bottle per tank for 3-4 tanks of high rpm riding over a 2-3 week period.  You should start to notice a difference around the second tank.  This has worked on two k100's for me.

No reason why cleaning your injectors has to be dull.
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Offline DJEwen

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Re: Fuel from exhaust - no start whackness.
« Reply #18 on: August 08, 2019, 05:26:17 AM »
Just buy a couple battles of Techron and put half a bottle per tank for 3-4 tanks of high rpm riding over a 2-3 week period.  You should start to notice a difference around the second tank.  This has worked on two k100's for me.

No reason why cleaning your injectors has to be dull.

That's effectively what I've done, Gryph.
  • Scotland
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Offline Laitch

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Re: Fuel from exhaust - no start whackness.
« Reply #19 on: August 08, 2019, 02:25:24 PM »
No space for a spanner, too long a plug for a normal socket, no space for a long reach, no space for purchase with pipe grips etc. I ended up hacks Seong the plug off then removing with a standard socket. New temp sender is en route.
You didn't go after it by removing the air box first and fetching it from behind the radiator?
  • Along the Ridley in Vermont.
  • 1995 K75T 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 DJEwen

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Re: Fuel from exhaust - no start whackness.
« Reply #20 on: August 08, 2019, 04:37:54 PM »
Is that the procedure? I removed the radiator first, the standpipe is straight upright and would have the same access issues from either side presumably? Itís the close proximity of the upper barb thatís the issue.
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  • 1985 K100 'Revive', 1987 K100 LT

Offline Laitch

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Re: Fuel from exhaust - no start whackness.
« Reply #21 on: August 08, 2019, 06:42:26 PM »
Is that the procedure? would have the same access issues from either side presumably?
Presumably?  :nono2: There seemed to be enough room in there when I removed the air box.

Here's mlytle's take.
 [ Invalid Attachment ]
  • Along the Ridley in Vermont.
  • 1995 K75T 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 DJEwen

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Re: Fuel from exhaust - no start whackness.
« Reply #22 on: August 09, 2019, 07:12:10 AM »
Presumably?  :nono2: There seemed to be enough room in there when I removed the air box.

Here's mlytle's take.
 [ Invalid Attachment ]

Hmm, I'd still argue the access to the fitting is a poor design as the above the barb is the problem, however, removing the air box is a much lesser job than dropping the coolant and removing the radiator! I'm happy however to see that my coolant was immaculate at least  :laughing4-giggles:
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Offline natalena

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Re: Fuel from exhaust - no start whackness.
« Reply #23 on: August 09, 2019, 09:07:33 AM »
Just buy a couple battles of Techron and put half a bottle per tank for 3-4 tanks of high rpm riding over a 2-3 week period.

No reason why cleaning your injectors has to be dull.

Just received Techron from Amazon Prime at $7.99/20oz bottles. Seemed to be a reasonable price for an in-vitro cure, and prophylactic.
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Offline volador

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Re: Fuel from exhaust - no start whackness.
« Reply #24 on: August 09, 2019, 09:31:05 AM »
IMHO that Techron stuff looks, smells, tastes, feels just like Kerosene
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