Running rough after clean & tune - tips?

Backgound: 3 weeks ago, my 82 650 began leaking oil out the rear main seal upon a start attempt. Bike would not start further. I believe one of the float needles got stuck and gas leaked into the engine over a few days, thinning the oil.

Ran through a gamut of repairs:
-Changed the oil twice (castrol 20w-50)
-Removed & thoroughly cleaned carbs
-Replaced a couple float needles & bowl gaskets
-Polished float needles, seats, diaphragm pistons & walls, diaphragm needle washers
-Float heights set to within 3 mm of gasket
-Two-bottle tuned the carbs, set mix screws to 2.5
-refilled & fully charged the battery
-checked plugs
-new air filter

Now, the bike runs worse than it did before the stuck needle. Backfires once in a while and rpms hang. Also, the idle is not the same every start. Sometimes after a warm-up it will be at 1300, other times 2000. It might hang at 3000 when I come to a stop, then when I start it up a minute later it will sluggishly idle at 1000rpm. Ran smooth as silk before gas got in the engine 3 weeks ago. Any suggestions?

 

Check for vacuum leaks. I usually use a propane torch - turn on the gas (do NOT light it) then just move it around the engine to see if there is a change in rpm's. WD-40 will work too.
The rubber caps that cover the tuning nipples sometimes crack around the top when removing to sync the carbs, causing an air leak when reinstalled. Also check the hose to the petcock, and possibly the petcock itself. (just put on pri, and plug the vacuum hose with a golf tee to see if there is a difference)

Not sure if that is the problem, but it's an easy place to start.

 

This bike is truly posessed. 3 days after starting it right up and running it with a strong newish battery (tested every which way) it now refuses to start. Going to put it on the charger and see what happens later today.

 

My first inclination is to say you tuned it wrong. I wouldn't have just arbitrarily set all the needles to 2.5 out if they already had a good setting to begin with. That is where counting the turns and putting them back to that setting comes into play when you are messing with your carbs if they are running correctly prior to messing with them. I have had carbs where one of the needles was as much as half a turn difference from the others in order to get its cylinder to run right.

I would also suspect the carb sync if you didn't use a good set of gauges or sticks. I have had weird idle problems like you describe before properly getting my sync done.

 

Did you synchronize the carbs? When they are way out of sync, rpm acted that way for me. There are many posts describing the theory and practice of syncing your carbs here.

Also, if you clean your carbs, make sure you get the three tiny holes labelled "F" (pilot) at the end of this post for a XJ550:

http://www.xjbikes.com/Forums/viewtopic/t=16515.html

It makes *all* the difference in idle rpm.

 

I checked for vacuum leaks and nothing happened. I'll try syncing it again in this weekend.

 

Synced again, painstakingly. No change. Did find a small vaccuum leak beneath one of the carb holders. I'm going to put some RTV sealant on their cracks.

I ordered a colortune too since I lost the initial mix screw settings. Maybe that will settle this engine down.

 

You said you got gas in the oil. Did the resultant diluted overfill possibly get pumped into the airbox enough to foul your air filter?

 

Doubt it, but I put in a new filter afterwards regardless.