Cylinder #3 doesn't fire until warm

not sure what this is... Every morning I go to start the bike, and only 2 or 3 cylinders will fire. After a few seconds of cracking the throttle and letting it warm, all of them start to fire. This morning I pulled the plug wires one by one, and all had an effect except #3.... The bike is running gloriously once warm, but even after sitting in the parking lot at school for an hour, it takes 15 seconds or so at idle for all the cylinders to fire consistently enough for a smooth idle. Like I said, the bike is running awesome besides.

I've been dialing the mixture, so I'm aware that I could be running rich and loading up plugs. It just seems odd to me that running a cylinder w/out spark for several seconds would actually cause the cylinder to fire....wouldn't that wet foul a plug? This makes me think its fuel delivery to that cylinder....

Let me know what you guys think.

thx

 

Troubleshooting a problem like this is twofold. Fuel mimics fire. Which means you need both for combustion. So a bad plug can make you think the carb is dirty and vise/versa. I would check the plug caps for the correct resistance which is 5kOhms. Replacing sparkplugs is not a bad idea either. One of the great things about tuning with a colortune plug is that you can see the sparkplug spark under compression. So that would eliminate a bad plug or plug wire/cap if you are dialing the mixture in with one. Still it is not uncommon for a cylinder to miss while cold. The fuel doesn't get warm enough to vaporize. Wet fouling is taken care of by the heat from adjoining cylinders and the exhaust pulling unburned fuel out.

 

Try swapping the plug with one from a cylinder that you know is firing when cold. (Check that they are the same plug while its out) If the problem follows the plug, get new ones. If the problem stays with the cylinder it could be a spark or a fuel problem. You can swap the coils to see if the problem follows the coil. IF that checks out OK, you have a fuel delivery or compression problem. I had a VW that would not fire on one cylinder when cold. It turned out that the exhaust valve was sticking when it was cold and it couldn't build good compression until the head (valve guide) expanded from the heat of the other cylinder on that side.