third pipe cold, but there's spark

HI
I've got this problem. There's a spark at the third plug, not worst than the other plug, but the third pipe still gets cold. I realise when i checked for sparks, that the plug smells gas, but it's the only one, the other plugs smells...normal. Last week i cleaned the carburator (cause third was overflowing) and make sure that i could see the light through every holes. Then i checked the compression cold (90;105;90;105)(should i test the compression with the choke on or off??)I exchange the wires between 2 and 3, and it did'nt change a thing, still the third pipe is cold.
What should i check??
Thanks for your help
Pat

Hi Pat, It was a good step to swap the 2nd and 3rd plug wires. If the problem stays on the 3rd cylinder, then that narrows down things to try. First, explain how you checked compression. Did you remove all plugs and hold the throttle open? The compression you note is pretty low and out of spec. Have you adjusted valve clearances? There is a "how to" on my web site.

Next, by shining a light into every hole on the carburetor, you were able to see light on the other side? I wouldn't think that is possible since most of the internal passageways bend considerably. Just a hunch but if you worked on the carbs, and you started having problems, I would suspect that there is a relationship. What did you do to the carbs?

Pat:

Most likely you have tried a new plug if not please know that a hotter spark is required to fire a plug under compression than one in ambient air, IE:
often times a used plug will appear to fire properly in open air but will not under compression.

del

About compression...yeah, your right, i forgot to open the throttle (i don't do that very often), and all plugs were remove and valve clearance were all right 7000km ago.
A moment ago, i try to leave the bike run for a while on three cylindre and the third just decide to run after 3 minutes of the warm up (!!???). So i don't really know what to say. I'll check compression right now.
Thanks

And about the carbs... I just cleaned them and reassemble the carbs just like it was.

Compression, cold, with throttle open 125;110;115;125. Still not very strong... I restart the bike and third pipe got hot. I check at the end of the exausts and the pressure going out of the exaust of cylindre 1 and 2 is a lot stronger than at the end of the other exaust, a lot stronger. Weird that compression test seems to show that it should be the opposite.
Does it help anybody??

The second compression check shows decently. It isn't perfect but certainly pretty decent. Well, keep an eye on the situation and get back if the problem shows back up! Good luck.

Does your motor have any smog devices on it? Was it first sold in the USA or Canada?

Bob