Cylinder 3 still not working?

[robgusto]

Hello, Sorry I have not posted in awhile because my friend was looking at my carbs as a favor. I have rebuilt carbs and rejetted with Dynojet for pods and pipes no megaphones. Compresstion at 120 to 124. Leak down test shows normal. Valve clearances adjusted to .004, gasket replaced, cam looked normal for age lobes looked good. Switched number 2 and 3 coil to confirm spark, used colortune to confirm spark also. Switched plugs multiple times. Adjusted air/fuel many times. I pulled plug after running and it was dripping wet with gas, pipe also has gas coming out. I hand cranked and the piston is moving normally. Myself and my mechanic and everybody else who has looked at bike are stumped???? Any ideas???

81 GS 750 L, KN pods, rejetted mikuni carbs, 2 into 1 pipes.

[chef1366]

Does the cylinder ever come on?

[robgusto]

the cylinder does come on at higher rpms. I can feel it kick in.

[chef1366]

take that pilot jet out and make sure you see light through it.

[robgusto]

I / my moto mechanic friend and I , had carbs soaked and rebuilt 2 x and a rejet. The problem has persisted throughout. Each time we take them apart we thoroughly clean all jets.

[OldVet66]

Have you switched your plug leads between two and three to see if it is the wire or cap breaking down. They fire together.

[robgusto]

Yes I have confirmed spark by changing 2 and 3 wires, confirmed with colortune, and confirmed by grounding plug to block and actually looking at it. It is getting strong spark. I am at the point where I may replace the motor 1st then carb #3 because this is such a crazy problem. The mechanic that worked on this bike said he has never seen anything like this problem. The other people (2 mechanically inclined friends) said that they will be able to figure it out, after a few hours they walk away scratching their heads and I'm out a 6 pack!!! I am naming the bike the ghost because the only thing I can think of is that the bike is haunted!!!

[MisterCinders]

I had a similar problem with my No. 3 cylinder. It is not totally sorted out yet because there are some lingering compression issues in that cylinder. One thing that worked for me was checking and adjusting the ignition timing. When I tightened that up, it ran much better, though No. 3 is still a bit slow to warm up at idle.

[robgusto]

Good to know I'm not the only one with this problem!! We are going to give it one more shot this weekend then it's to plan B, NEW MOTOR... I found a couple on Ebay for around $600. Any other places to pick up a motor? I may need to start looking for one...

[OldVet66]

I had had intermittent problems with firing until I switched to the Dyna green coils. The stock coils were new when I started my project, but one of the pipes would run a lot cooler than the rest. It would fire at higher rpm's but drop out at idle. Once the coils and wires were changed, the problem went away.

[robgusto]

I did confirm solid consistant spark several different ways but I may try new coils before I replace the motor. I just have a hard time doing it when the spark for #3 fires #2 perfectly.

[gearhead13]

The #2 carb has the vacuum plug on it, if it was that one i would suspect a failing petcock.
The fact that at higher rpm the cylinder kicks in means that your ignition is not the problem.
I would suspect maybe the floats arent shutting off the gas properly. Or maladjusted float heights. I would check that the fuel shuts off with the floats lifted up.

[robgusto]

All floats heights have been adjusted or checked when rebuilt. One was bent a little bit but it was for carb #1, it was corrected. The prev. owner eliminated the vacuum style petcock and now the current petcock does not have the vacuum hose, it has a cap on the #2 carb to prevent the leak. I have been told that this should not be an issue but at this point I'm considering everything!!!

[gearhead13]

All floats heights have been adjusted or checked when rebuilt. One was bent a little bit but it was for carb #1, it was corrected. The prev. owner eliminated the vacuum style petcock and now the current petcock does not have the vacuum hose, it has a cap on the #2 carb to prevent the leak. I have been told that this should not be an issue but at this point I'm considering everything!!!

Ok, but have you checked that the float/seat seal properly and shut off the fuel when the floats rise?
Pull the carb bowl, hold up the floats and turn on the petcock, no fuel should flow at all.

[robgusto]

I will double check tomorrow and post again. I have replaced all O rings and I believe everything is seated well. I'm not getting any overflow or leaks when petcock is left on, but I will definitly give it a check tomorrow.