Had a similar problem in May 2010. Back then, I added coil relay, new D8EA plugs all around and just plug wires and caps on 1 & 4. That seemed to solve all. Just did the the caps/wires 2 & 3.
Swapped 2,3 plugs caps and 3 still 3 cold. I measure header temps with an infred therometer. Will see anywhere from 400 F to 850 F on 1, 2 & 4 depending how long it runs and what RPM. Can light a cig off 4 once and a while. Seems to rev fine, but I limit revving it with one cyl not working. #3 runs about 130 F.
Compared spark on 3 & 4 at the same time and both were yellowish white. Since 2 runs fine I don't thinks it the ignitor. Might compare spark on 2 & 3 to see if that coil can make both spark. Have not done a coil swap, maybe I'll try that too. I also checked for stray arcs in a dark garage with the headlight fuse pulled. Nothing, all well and pushed and moved them around without getting poked. Forgot to wet them down first though.
Measured compression last night with the engine cold I did 2 rounds. # 3 was 210 psi on both rounds. I reversed sequnce and let battery recharge between rounds. # 2 was 165 (last on R1, then 195 on R2. # 1 was 217 & 225, # 4 was 225 & 217.
Valve adjustment was checked in May, maybe 2000 miles ago. It seemed allright, although I'm not an expert on how well the feeler gauge should feel. It also has a new honda r/r giving correct voltage to 1 year old battery and a new fuel filter. Battery maintains 12.8 volts between rides. About 13.5 after charging or a ride (maybe). Have Vice grips clamping off the vacuum line to # 2 and feeding fuel via a funnel & beer bottle (Sierra Nevada Pale Ale) to the carbs. I also undid the carb drain on # 3 and gas came out.
I also sprayed WD40 around #3 & 4 intake boots, might have heard rpm go up 25 or 50, but #3 didn't warm up.
Since gas flows from 2, to 3 to 4 on the carb tubes, and 4 runs, # 3 should at least be seeing fuel.
About the only thing I'm considering besides from a complete re-clean of #3 carb is a set of dynateck green coils. The plug wire I used came from a bike shop and I hope it's non-suppression. It has a copper core, surrounded by white insulation and a black jacket. I also measured resistance on caps and cap wire assemblies. There was no change and about 4.73. NGK VD05F caps all around.
Should plug wires be routed under or over the main frame tube? Seemed to me I had a difficult time getting the tank on after the coil relay (its under thank)
and may have had some wires going over the tube. All in all, I'm thinking 4 straight caps instead of the V might be better for keeping wires away from the valve cover.
On # 3 carb is a stuck float a possibility? Leaky CV boot? Crimped breather tube, leaky fuel pipe? Somethng on the needle jet? Dead Mouse in the carb? I hate taking off/on the carb rack. So if there is anything else I should do first, besides sell it, I'm game. I also bought a new air filter, but haven't put it in yet. Just also bought the tappet feeler gages. 004 up to .008. My friend has a set of green dya coils on his Kaw, but that's asking allot to swap themover for a try out. If he offers though...
Have to finshing painting the house, another bike that runs fine, 2 cars to fix and 1 car running, so time on the GS is limited right now.
Eric,
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