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3rd cyl not firing

  • Thread starter Thread starter Hammer
  • Start date Start date
H

Hammer

Guest
Daddy, my hat fell off!

Hey guys,

I've got a head scratcher here on a 1979 GS850G Suzuki. It's a 4 cylinder and the number 3 cylinder is not firing. There is spark but the pipe doesn't get hot. The other 3 pipes are so hot you can't touch them for more than a second.

Anyway this bike has the old type of carbs - not CV. The fuel screw had a broken off tip at one time. I guess the PO had to dig the broken tip out possibly enlarging the hole. I have just got the bike back together after replacing rings and one valve and it runs but only on 3 cylinders. It did this before I tore the engine down by the way. Also, it has contact breaker points and condensors instead of electronice ignition. I replaced those and I was worried I didn't get them set right but the #2 cylinder fires ok.

I have adjusted the valves and was going to sync the carbs but I don't think there is any use in that until I get that cylinder working.

Any thoughts? I am thinking it is a carb issue and if that screw has anything to do with it I don't know how to fix that other than replacing the #3 carb body or getting a whole new set of carbs.

Thanks for any comments.
 
swap the plug leads and see if it moves to #2... if not it most likely will be the carb.. maybe gettting too much fuel and flooding the spark. The coil sounds like it is okay but you mayalso have a weak coil... giving a weak spark when the cyl is at full compression.
 
The older slide carbs have the petcock vacuum connected to the #3 carb I would start their
 
SqDancerLynn1 said:
The older slide carbs have the petcock vacuum connected to the #3 carb I would start their
Click to expand...

Right, your petcock could be screwed up and sucking gas into #3.
 
Do as Joe says and swap no's 2 and 3 around and also swap the plugs and caps.Just because they spark on the head does not mean they are sparking when fitted.If the prob is still apparent,then go #3 carb.
 
Bad storm last night. Had to clear the garage so the wife's vehicle could be brought in so I haven't got back to work on it.

As far as the petcock goes -I'm using an auxillary gas tank so there is no petcock connected right now.

I will check all the things suggested here.

Thanks.
 
I assume you do have the carb #3 vacuum port plugged while trying to run the bike without the tank? An "intake" leak that big wouldn't allow that cylinder to combust well.
If that's OK, then a possible enlarged pilot fuel screw hole wouldn't cause a no combustion problem. Yes, it would richen the mixture at idle/minimal throttle position and cause some tuning trouble but that's all. I don't how much the hole was enlarged, if it was, but that sharp tipped/tapered screw would generally be one turn out from the factory, so you would be able to turn the screw in one full turn, at least, to compensate for the larger hole. And a larger hole would most likely allow even more inward (leaning) turning. Of course, you need a good screw to work with. The pilot jet itself would still be what's regulating most of the fuel flow at idle. The pilot fuel screw regulates a secondary passage and is for fine tuning the pilot circuit mixture only. It "assists" the pilot jet.
If you still have a problem, is the plug at #3 getting wet with fuel after cranking? If sparking, it figures there's no fuel on the plug.
 
Thank you guys. Problem fixed. It was as simple as the 3rd cylinder vacuum hose not being plugged. Man I feel dumb but I guess that is how you learn.

Thanks again.
 
Hammer said:
Thank you guys. Problem fixed. It was as simple as the 3rd cylinder vacuum hose not being plugged. Man I feel dumb but I guess that is how you learn.

Thanks again.
Click to expand...
Simple things are easy to over look. I thought I'd mention it because others here have done the same thing at least a few times in the last year.
We're all learning here.:)
 
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