wierd ignition problem or misfiring cylinder?

[ccs]

Hello All;

I have a 1982 GS-850GZ with about 29,000 miles. It has been running fine since I got it in May of 06 with 19,600 miles on it.

I put a MAC 4-1 header on the bike (but not the muffler). I have not had the time to re-jet the carbs so the bike is running a little lean -- you can hear it sputter and hesitate during a fast acceleration.

About 3 weeks ago, I developed a wierd problem -- when I start the bike, or come to a stop, the RPM's will drop to 300 or so and the bike will stall unless I rev the engine -- and the engine sounds sick -- like it's running on 3 cylinders. Sometimes, reving the engine will get all the cylinders firing again and they all seem to fire OK when I take off because the bike runs and sounds OK.

Not sure where to start looking.

Does anyone have any advice on where to start looking or how to start diagnosing the problem?

TIA.

Charles...

[ta473]

check the #2 plug if its carboned up replace your petcock. my 82 gs1100 with 28763 miles just did the same thing

[fgh]

Check all the plugs. What do they look like?

[chef1366]

You're running the bike with no muffler-baffle?

[ccs]

check the #2 plug if its carboned up replace your petcock. my 82 gs1100 with 28763 miles just did the same thing

I pulled all the plugs. #2 looks normal, #1 looks normal, #3 looks a little white (on the lean side) and #4 is a little black and sooty.

So... I guess it's not the petcock.

I cleaned all the plugs with a brass wire brush and swapped #3 and #4. Started the bike and it soundded OK, then all of a sudden the RPM's dropped to 200-300 and then it stalled. Started it again, and it's OK, then no, then rev the engine and it's OK, then not.

Any ideas on how to diagnose what's going on?

TIA.

Charles...

[nabrams]

Have you tried NEW plugs? That black one could be faulty.
If you still get the same problem even with new plugs, then you need to suspect the ignition components and plug wires/caps - been discussed a million times - do a search.