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#2 will not fire

  • Thread starter Thread starter Vinylfork
  • Start date Start date
V

Vinylfork

Guest
Hi, anyone up for a challenge? I?m kind of stuck!

I?m not sure where to post this because I can?t figure out where the problem is. carb / fuel / exhaust / ignition / electrical
I definitely know it has something to do with my knowledge, so I turn to you, the wonderful people here at theGSResource forum.

Case:
#2 will not ignite/start/fire, #1 #3 and #4 runs fine.

Object:
?78 GS750e (that has not been used for about 3 years), with mikuni carbs, ND coils, ngk b8es plugs.

The problem hunt:
I started of with changing all the spark plugs, and the caps. Cut the wire and reattached the caps and wires. #2 will still not fire. I swapped the wires on #2 and #3. no change.
I took out the carbs, cleaned, made sure the gas had a way through. Still no change. I know the gas is coming through, cause the plug is wet after I start the bike for a minute. I then read somewhere that if the ignition was wrong on #3 it could make #2 not fire properly, so I fine tuned the ignition as well. But still no change.
I took out the coils, and had them tested. The spark is weak but works, (yes, I am ordering new ones.) I swapped the electrical wires on 1-4 and 2-3 coils and swapped the wires to the plugs around too. And the problem did not move from #2 to #1 so its not the coils either.
My immediate thought was: oh-crap the compression is gone. So I tested the compression, but it was the same as all the others. It?s not very good compression, but it?s still ok. About 110 (should be about 150-160 from what I read)
Next thing I checked was to see if the exhaust actually flows freely out, but instead of taking of the top, I just took of the exhaust pipes and held my hand in front when running the engine only on the starter, and it pushes my hand away, so the problem is apparently not there either.

So now I am kind of lost, I just sit there in my garage and stare at it, but that doesn?t seem to help much either.. :)

I am going to buy a can of starter-gas today and test. I read about someone who suggested that for someone else in here that didn?t get #1 to fire.

But other that that, any idea anyone?
 
Last edited:
" I am going to buy a can of starter-gas today and test. "

First, make sure we agree to call #2 cylinder the second one from left as we sit on bike.(#1 is under clutch hand). Do you have a vacuum operated petcock with vacuum line attached to #3 carb (third from left) ?
 
" I am going to buy a can of starter-gas today and test. "

First, make sure we agree to call #2 cylinder the second one from left as we sit on bike.(#1 is under clutch hand). Do you have a vacuum operated petcock with vacuum line attached to #3 carb (third from left) ?
Yes, we can agree on that!
and yes I have a vacuum operated petcock, and the vacuum hose is attached to #3
 
First measure the #2~3 ignition coil's resistance from plug cap to plug cap and record. Then remove both spark plug caps (boots) and measure the end to end resistance of each plug cap and the end to end resistance from bare coil wire to bare coil wire; record and post the results of those measurements.

Post your results.
 
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