My 82 XJ750 Project

Here's a little preamble to my situation. In a nut shell, the bike was last insured in 2010 and has been parked since. After a carb clean and an oil change I got it started but it idled high (about 1200) and a little rough. The following day I tried to start her up...didn't spend enough time on the damn enrichment circuit. Will remedy.
The feeler gauges I borrowed weren't thin enough for a check on clearances so I went ahead and did a compression check...numbers.
Cold:
Cyls 1,2 and 4 between 115 and 120
Cyl 3 70...Damn!
Warm:
Between 120 and 125 across the board
After a bit of oil in each cylinder jumped to 140 to 150 save 4 which hit 180?!
A couple of other things I checked along the way:
Warmed up it starts fine on 3 cylinders as long as both 1 and 2 are hooked up. Otherwise just a buch of chugga chugga
Also the exhaust pipe on 3 gets way hotter way faster then the rest, like bounce your spit of of it while the rest dont sizzle a bit.
I hope someone can make sense of all this info.
Cheers,
Chrome

 

Sure. #3 has a way-tight exhaust valve. Or that cylinder is running really lean.

QUIT RUNNING THE MOTOR.

Get the valves in spec; and then re-run your compression tests.

Invest in a set of metric feeler gauges; K-D Tools' pn 2274 is widely available, on the K-D Tools "special tools" rack at many Auto Parts stores, Sears, etc. That will help prevent consternation converting American to metric.

Meanwhile, stop trying to run the motor. From the sound of the "wet" test, you're probably fine right now; don't hurt it by trying to run it until everything is sound. You could also have an uber-LEAN condition in #3; let's don't burn a valve or hole a piston by getting ahead of the game. "Hillbilly tuneups" don't work, running it won't suddenly make it better.

You said you did a "carb clean." How clean? See: http://xjbikes.com/Forums/viewtopic/t=14692.html and http://xjbikes.com/Forums/viewtopic/t=2908.html

Did you then accurately WET SET the float levels to their millimeter-tight specs? http://www.xj4ever.com/setting%20fuel%20levels.pdf

Do you have a service manual yet? If not, track one down.

Meanwhile, these will help with the valve adjustment: http://xjbikes.com/Forums/viewtopic/t=14827.html
Part Deux: http://xjbikes.com/Forums/viewtopic/t=29209.html

 

Done.

In the process of getting some. My location, an island off the coast of BC, means that getting special tools is never as easy hopping in the car and driving to my nearest automotive shop.

I'll take another crack at them. I feel confident about what I did do but I did miss some of the cold start circuit elements on the top end.

Yes and yes.

Thanks for the info Fitz and Happy New Year!
Chrome