86 K75 Won't start, has fuel and spark - K-Bikes.com - Excellence in Motion
 
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post #1 of 7 (permalink) Old Aug 13th, 2013, 5:49 pm Thread Starter
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86 K75 Won't start, has fuel and spark

Hi guys,

I am a fairly experienced motorcycle mechanic, but as you know these bikes are quite unique and complicated due to the early fuel injection systems. A friend bought an 86 K75 that a guy had ridden from Montana to Texas, he said it died on him here so he flew back. First problem was a dead fuel pump, easy enough. Replaced it with an aftermarket pump, cleaned the tank, new filter and lines, cleaned and checked all electrical connections etc. new fuel pump works great and has 36 psi at the injector manifold.

The battery voltage is good, it will turn over, has spark on all 3 plugs, and I removed the injectors and have seen them pulse fuel spray simultaneously. Compression on all cylinders is above 170 psi as well. I followed the troubleshooting flow chart I found and traced the problem to what I thought was a bad air flow meter, which failed the tests for both voltage and resistance. However when I replaced the air flow meter, the bike still will not start. Air filter is also in good shape and no nests or blockages.

I've cleaned the grounds, checked everything I can think of, and read 20 pages of "no start" posts on here. The only thing I can imagine is that some sensor related to timing is off so it sparks when the valve is open, I have heard it puff and hiss while trying to start it.

Any help would be greatly appreciated, I am at a loss as to how it won't run with the injectors pulsing, good spark, and compression. Thank you
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post #2 of 7 (permalink) Old Aug 13th, 2013, 6:49 pm
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Here's what I'd do:

Try jumping power to the fuel pump. (Smaller terminal is positive.) Sometimes the fuel tank connector fails/is flaky. It's possible that the vibration of trying to start it means the fuel pump is getting intermittent/insufficient power.

Check the soldered connections on the back of the ignition switch. When the switch is all the way clockwise the green wire should have continuity with the red wire. The gray should have continuity with the gray/blue.

If it's getting spark then it's probably not the Hall Effect sensor. (timing)
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post #3 of 7 (permalink) Old Aug 13th, 2013, 7:23 pm
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Quote:
Originally Posted by FlyingDuck
Here's what I'd do:

Try jumping power to the fuel pump. (Smaller terminal is positive.) Sometimes the fuel tank connector fails/is flaky. It's possible that the vibration of trying to start it means the fuel pump is getting intermittent/insufficient power.)
I know people who are running Ks with the fuel pumps wired so that they run continuously. Hasnt seemed to have had any ill effect. My fuel pump connector failed. Prior to its death I was experiencing intermittent fuel starvation. Sometimes it stuttered when running. Sometimes it wouldnt start. Took me a while to run it down. You should be able to hear the pump running. Listen for it when you try to start the mc the next time.

I take it the starter is engaging from the remark that the mc sometimes hisses and such.
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post #4 of 7 (permalink) Old Aug 13th, 2013, 8:02 pm Thread Starter
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Just to clarify, the fuel pump is working properly now. I can hear it running while cranking, as well as see the injectors spray fuel during cranking when I pulled them from the cylinders. Fuel pressure is 36 psi as required.
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post #5 of 7 (permalink) Old Aug 14th, 2013, 1:11 am
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Try re-installing the Motronic computer that's underneath the seat. Make sure the contacts are clean and the plug is fully seated. If you have another Motronic you can substitute for testing (to check if yours is bad) try that too.

Tim
1991 K75-RT
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post #6 of 7 (permalink) Old Aug 15th, 2013, 1:31 am
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After doing recent clutch work, the K100 refused to start. Had power and fuel. I pulled the plugs and checked for spark. Fine. Out of desperation, I put in new plugs. Fired right up.

You didnt mention if you had the mc running earlier. Any chance someone pulled the caps off the plugs and then put them on incorrectly?
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post #7 of 7 (permalink) Old Aug 15th, 2013, 10:52 am
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Fuel?? Is it getting through the injectors? Considering all the other things....tank lines and pump they may be plugged. All of them have a little inlet filter screen.

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