Cylinder #2 not firing

'81 XJ650 Maxim. I recently rebuilt the carbs, cleaned very meticulously, replaced throttle shaft seals and fuel o-rings, float needles and seats. Made sure all the diaphragms are good without any holes and are seated well in the grooves using some grease. Clunk tested well. Had trouble with high idle but cleared that up by blasting carb cleaner through all of the pilot circuit with the jets and idle mixture screw off. Bench and vacuum synced. Compression checked and is good. Valves checked and all within specs, but on the tight end of things. New spark plugs/oil/oil filter changed.

Now it seems to be idling well and runs, but cylinder #2 is not currently firing. When driving it seems to be lacking a little bit of power, and occasionally the cylinder will fire and I can feel the bike really start to take off. After a ride the #2 exhaust out of the front of the bike is only lukewarm, where the others are scalding hot.

I have tried switching the #2 and #3 spark plug wires to see if there was an issue there, but the same thing happens. #3 runs just fine with the #2 wire. I checked the resistance of the #2 cap and it is fine at 5k ohms. I might be wrong, but this suggests that the electronic side of things is ok...if #3 is running fine even with the #2 wire it would seem the wire, cap, coil, TCI, and everything else is ok. The only thing I can think of for this is that the coil is weakening and only able to provide spark under pressure to the cylinder with the lower compression(#3).

I have switched the spark plugs all around with the same results, just problems in #2, even using the old plugs in the mix. I have tried adjusting the pilot mixture screw to both richen up the mixture and lean it out without any help. When I pull the plug off after it has been running, it is wet with gas, and the exhaust smells of gas and spits some out.

I just checked the compression today and cylinder #2 was the second best at 130psi, just below #1 and about 10psi better than #3 or #4( I know thats not great but should work), and did another vacuum sync right after I did that. I also checked the fuel levels while on the bike, and carb #2 was right in line with what was going on in #1, 3, and 4.

I am running out of ideas at this point, any help is greatly appreciated!

 

Your #2 carb has a persistent plug-uppage somewhere; or the enrichment plunger isn't fully shutting off and you're flooding in #2 only.

 

Thanks! I took the carb apart again and checked all the jets and everything else. It turns out the main air jet under the diaphragm was plugged up(thought I checked all those, guess I missed it). Fired up and at first the pipe wasn't much different, but now it seems to be the same, and with lots more power!

 

Sounds nearly idenical to my xj750K problem ... except it's my #1 carb. I'm gonna ultrasonic I think however all jets are clear.