I have a 1985 Yamaha Phazer, the sled will start fine and it sounds ok, but after a few minutes it will foul out the plug on the cylinder next to the fan, any ideas? I cleaned the carbs but this is my first time with Yamaha carbs, it was given to me because the previous owner couldn’t figure out what was wrong. is there a mixture screw that would cause it to run to rich? Anything that would cause it to run to rich? I checked the needle and seat also, it also seems to close when I push the float up, I hooked a piece of gas line to it and blew into it then pushed the float up and air could not pass through, could it be timing or intermittent spark? but the engine sounds fine till the plug fowls then it will backfire and run rough, I did a compression check and the two cylinders where almost exactly the same, with in about 5 or 10 pounds, about 150psi. my guess is that it is running to rich but I cant figure out why... is there a way to test the coils or stator plate?
Check the choke cable on the carb for that side. It may not be bottoming all the way in the bore. You should be able to see a little bit of free play (.5mm-1.5mm) if you pull the rubber boot off the adjustment nut and pull up on the cable.
One other thing to check is the fuel pump. If the impulse line goes to the cylinder that is fouling it is possible that the pump diaphram is leaking. Pull off the impulse line to see if it has gas in it. If so rebuild the pump.