1 lean cylinder

So I've nearly knocked out every problem on my 81 xj650 but I now have one very lean cylinder. I want to try and fix it with needle shim but just want to know if it is even worth a shot. I remember when I put my carbs together after cleaning them that one of the springed attachments to the enrichment circuit (where it attaches to the bar that engages with the choke) was a bit taller than the others. I'm not with the bike right now but if indeed it is that problematic cylinder, is it possible the tiny o-ring was dislodged when I reassembled and is now letting in too much air? I'm running out of things to test but I just wanted to know if that is a possibility. My plug is quite white and have some seen success of shimming the needle. With it being one cylinder what possible engine issues would I be looking at if the carbs check out?

 

I had a lot of trouble on my XJ650 with the gaskets to the motor on the intake boots cracking and sucking all hella air. Have you checked that?

Mine eventually had a lope at idle, you could tell one hole was weak. When I'd partially cover that carb throat, it evened up. I knew I was sucking air then. Don't cover the venturi at the top of the throat, that makes weird things happen ...anyway, soaking with WD-40 while running finally found the leak...both times on the bottom of the gasket, had to spray up at it to hit it...starts idling right as it sucks it through...

After two did it in the same summer, I got smart and replaced them all...

PS those gaskets are like $11/each from a dealer...I just bought a roll of Fel-Pro bulk high temp gasket material for $6 and cut my own, using the boots as a template....

 

Are your valve clearances in spec?

Otherwise, a vacuum leak is a real good possibility.

 

I needed a bit of a break from the XJ to regain some sanity. Constant fishing in place of constant troubleshooting seems to have done the trick. I checked valve clearances again the other day and it turns out I have #4 exhaust reading .10 and thats a new OEM shim from Chacal. #3 exhaust is reading around .23 I believe. I cant remember correctly and I seem to have misplaced my sheet with my readings, but I think there is one more that is tight. Everything else is in spec including my problem #2 cylinder both IN and EX.

Either I have 2 that are tight, #4 EX and whichever other, and 1 that is loose #3 EX or its just the #4 and #3. I just remember two being out of spec, but I may have let number 3 slide as it was so close and on the loose side. I am an idiot and didn't pull the shims as I was pressed for time. For my next question just roll with this approximation.

I want to ride this bike about 50 miles per day, 25 each way, until the 20th, when I get my paycheck and then get correct shims. Is this possible with this lean cylinder? I redid gaskets for the intake boot and completely sealed the thing in RTV black where any cracks were (they didn't appear to go completely through. The bike runs pretty well right now, and idles like a champ. I turned it on today and with choke it pretty much started right up. I've read I can mix two stroke oil in with the gas to help lubricate the cylinder to prevent any damage from the lean condition. Would this help, or still be dangerous?

My other theory is to fudge the throttle adjustment screw on the #2 to get the cylinder running richer because I know that at one point it had shown a bit of color. Would this make me run just a bit rougher? Maybe need higher idle or something?

Any advice is appreciated, I know I need to sort the valve shims and will get to it when I have the money. Thanks.

 

If its running well, I would not mess with a sync screw to try and get the cylinder to run richer. If you are going to adjust anything it should be the mixture screw on that carb.

 

Mixture screw isn't giving me any change. Its a pretty clean white that I'm dealing with. I even attempted to shim the needle. I took a guess and just inserted the needle through the washer and then reinstalled the needle. I took a washer from one of the cap screws on a spare set of carbs and it fit really well over the needle. This gave me no change. I'm convinced its the sync mismatch from the incorrect valve shims. Do you think the oil in the gas will provide enough lubrication for me to ride it?