Ongoing Idle issues. Vacuum or jetting ??

To All XJ brainies out there. (81 KJ750) My bike runs well from 1500 rpm and up, it still struggles to idle smoothly and stalls. If I idle over 500 rpm, it hangs at 2500rpm when running. There's a fine balance point of around 400 rpm I can adjust to (sometimes) but too often I stall if I don't keep playing the throttle.
Sometimes I get hestiation at hard acceleration above 6000 rpm, but usually OK
I've done the following;
-Church of clean thorough strip down and cleaning of all carbs, including the low idle port, integral to each bowl
-had carbs syncd by professional WITH YICS stick. He showed me video and above idle, carbs look good. He also struggled to get it idling properly
-clean air filter with stock airbox,
- fresh plugs, They have nice gray look to them
-checked all valve clearances and all good.
- floats were all leveled (wet)
So... Last night I tried spraying starter fluid around the carb seals and boots to detect a potential vacuum leak. Nothing changed. HOWEVER, when I sprayed a small amount into the air box, her idle smoothed out quite nicely. I'm not into carrying a can of starter fluid with me for stop lights..lol...
Vacuum leak somewhere, or jet setting ??

 

I meant XJ750 (damn opposed thumb evolution..)

 

If you went to Church did you verify that the correct jets are in place?
Who is the "Professional" that synched your carbs? If it ain't you I wouldn't trust it.
Idle RPM should be 1,050(ish) - your idle is far too low. Did you colortune after the carb cleaning?

 

Thanks for responding.
Yes, jets are correct size
He's a bike mechanic. Used to own an XJ750 and knew all about the YICS stick requirements, etc. He showed me a video of gauges after syncing carbs and except for during idle, they were all consistent. I cannot guarantee he did a good job, but with lots of experience dealing with mechanics and knowing enough to call B.S., I think he's legit.
If I set idle above 600, the engine with "hang" at around 3000rpm when I decelerate. There seems to be a problem transitioning from mid rpm to low idle when I set the idle within proper range.

 

The throttle shaft seals were replaced?

 

No. I realized I forget to check this after re-assembling the carbs. That's where I'm wondering if there's a vacuum leak. I was hoping that spraying the starter fluid would show the leak by a change in idle when it gets sucked into the air stream.

 

Ding ding ...then you did NOT get down enough if you broke the rack and submerged the carb bodies without full tear down this will eat the rubber seals on the throttle shaft seals. Your carbs need a bench synch needs to be set best with 2 playing cards cut in 2 put them under each butterfly adjust till you get a little resistence. Hold up to light you should see just a little light. This means your close... then do a running synch I prefer the 4vvacuum gauge set up. 600 rpm is way to low 1050 to 1100 is where you want it.

 

I didn't break the rack to check/replace the seals. That could be my issue. Looks like a saturday afternoon carb re-re-build is on my menu. I was afraid of that.

 

In order to replace seals you have to remove 2 screws on the butterfly plate and remove plate remove nut on shaft and pull shaft out. This is why you have to " break the rack" remove carbs from rails . Why your at it replace the O rings on the fuel rail ..

 

And when reassembling tighten the nut FIRST before tightening the butterfly screws . . . . ask me how I know.

 

Don't fear the reaper.....

 

Tear down carbs use a few cups or bowls so you don't get anything mixed up . Once all rubber seals are out. Get a 1 gallon container of BERRYMANS carb cleaner Autozone . Soak each carb body for about 45 minutes each . Reassemble with new seals and a dab of blue locktight on butterfly plate screwes there are 2. On each carb .A few beers and should take an afternoon

 

I actually soaked the carbs for 24 hours using pinesol. Read this by a few people as a good alternative and environmentally better. I was very impressed as it cleaned out any trace of dirt and residue. This was last year when I rebuilt carbs. At this point, all I think I need to do is the seals. Thanks guys.