Dead cylinder XJ700

It starts and runs, but I believe that cylinder #3 is misfiring. It has spark and compression (150+), but I don't think it's getting fuel. The carb bowl has gas. The exhaust pipe is just warm, not smokin' hot like the others. The plug shows no signs of combustion - still relatively clean. I think the pipe is warm from the surrounding cylinders.

Also, it revs to the moon when I use the enricher just a little, but it will idle when I feather it to just the right spot.

Background: Bike sat for about 4 years, not run. 20k miles. Bought from original owner, dealer serviced w/receipts. Bowls somewhat varnished when opened, nozzles partially clogged. Totally stock, incl. airbox and pipes.

Work done:
1. very good carb cleaning, completely disassembled.
2. I took the caps off the pilot mix screws, all backed out 3 turns now. Bench synch'ed only.
3. intake manifolds removed and resealed w/gaskets and Permatex.

My theory:
1. jets clogged on #3, particularly the pilot system.
2. intake valve not opening ..? I see this as almost impossible. There'd be a terrible racket in the head from broken parts.

Your ideas will be appreciated. Thank you.

 

I see you said you sealed the intakes but man it sure sounds exactly like what mine did with a gaping intake flange leak....and sucking air will make them rev like hell with the choke on.

Take your airbox to carb boots off, and choke out each carb with your hand while it idles. When you find the one sucking air it will rev rather than bog. Then you've just gotta find the source. Spraying WD-40 around while idling works pretty good, it'll react when it gets sucked into the problem.

PS, I did the same thing, pulled carbs and cleaned, before realizing what the actual problem was.

Anyway, try choking them out individually...this will verify if it's a lean problem on one.

 

Also #3 is the one with the vac line for the petcock, no? Check that for leaks as well...

 

Jeffco - thanks for the idea and I'll try that (choking each carb throat.) #2 has the petcock vac line, but the other rubber caps could leak, too. I agree with you about the intake flanges and fiber gasket - potential there for considerable leaks.

Had the carb set off several times up to this point, of course, but this time I'm gonna take the hat off #3, remove the diaphragm and slide, remove the pilot adjustment screw, and blow air down the orifices. Drain the bowl to take pressure off the float tang and needle (delicate parts.)

I don't think that'll damage the float or float needle if I take it easy. Or, remove the carbs and bowls again and check the jets for blockage.

If the pilot jet was blocked, or its feeding hole in the bowl, then the carb is only sending fuel from the enricher, it would seem. (half to wide open it's getting fuel from the main.)

It screams with the enricher on even partially and very slow to rev down.

I'm leaning (so to speak) towards fuel blockage in the jets over air leak. Even with an air leak, the exhaust pipe would get hot - very hot. The pipe is warm, at best, after running a couple minutes.