Cylinder #2 not firing

So now I have my bike working in a somewhat decent order, except that I am still have troubles with it running well.

I think what WiredGeorge had thought earlier might have some play in this problem, but I will ask to make sure.



When I start the bike cold, it runs mint. Starts right up, sounds nice, revs nice, real zippy too. About 2 minutes later, I'm pretty sure cylinder #2 stops firing, and the bike starts running hard. Almost like it is bogging, full throttle almost kills it, sputtering like it is choked, also I can hear what resembles air whooshing somewhere. Weirdly enough, when I let it rev down for a few seconds, and then re -rev it, it is good for a second or two, then sounds like a lawn mower engine again, almost dying.



Reason for suspecting cylinder#2 is that after running it for a while, I noticed it is not as hot as the other pipes, and the spark plug in it, looks 3 times newer than the other 3, all were replaced at the same time.



For anyone that didn't follow the other thread I had the last week or so, I have checked the compression and all cylinders are very similar, showing minimal ring wear. So compression is relatively good. I am wondering if this is related to the valve or whatever not closing enough when it gets warm or something. It seems to be related to when it has warmed up a bit, though maybe that is just random..??. I have also check for a spark on #2, it has spark.... I don't know how "good" of one, but it definitly has spark and I know that the firing order is correct.



Thoughts??


Thanks again to all who helped before. Great job.

If you havent checked the valve clearance? If not you should.Sounds to me that you might have come tight valve clearances.As the engine heats up the clearances get tighter as for then keeping valves open,losing compression so not power.BTW what size and model bike is it along with the year?? You can go into your profile and add these into your signuture line.

Rammy, I second your request that B4 add his bike year/model and his location to his signature. I can't remember all info from all threads and it wearies me to keep asking... "what bike"?

I will also say that if he has decent compression and it doesn't vary across the cylinders, then while he may need to adjust his valves, they probably are NOT hanging open and are problably NOT the reason for his #2 cylinder to not fire. This seems to leave either an electrical issue or carburetors.

ALWAYS troubleshoot the electrical FIRST. Initially, verify that #2 isn't getting hot. Warm the bike a bit, then use a spray bottle. First spray on #4 and see that the spray is immediately vaporized. Then... try #2. If the spray is vaporized, you were wrong. If it isn't, although the pipe is very hot, the spray will run down to the ground and not be vaporized. For grins, also check the other cylinders... just to be sure your impressions on which cylinder(s) were not firing are correct. IF it was just #2, then proceed to next step. If another cylinder IS NOT firing, come back and report that in this thread.

#2 not firing?
First, swap the #2 and #3 plug wires. See if problem moves. If it does, the problem is in the plug wire, the plug cap or the plug wire's connection to the coil. If it stays on #2 cylinder, swap the #2 and #3 spark plugs. If that doesn't move the problem, the problem is in the carbs... repost the problem in the carb section.