Poor idle #2 cylinder has no to low vacuum Can't set sync

Bike was running perfect all spring... bike fell over and lots of oil into airbox, cleaned everything up and 30 miles or so later started to idle poorly. Not sure if it's accident related ?
Installed sync tools and blocked the YICS system with some vacuum hose, and #2 cylinder [right to left] will not sync, mercury fluid will not rise, I think the butterfly screws may be out of basic adjustment and I'm not sure how important that is because early this spring I was doing a sync and it ran out of fuel and I was messing with the screws all over the place and it never seemed to sync right after that ,the idle would come down slower then it use to.
Is there a basic setting for the butterflies that I can set on the bike to start over with. or should it set up with the sync tool not matter what your base setting is which I suspected it should do ?

Putting propane or carb spray into cylinder 2 makes little difference.
No Vacuum leaks.
Compression good starts at 110 first pump and to 150 psi total.
Valves within spec.
I am pulling my hair out on this one and I don't much left of that ether.
Has any body been down this rode before ?
My next step is pulling off the carbs and that's getting bit long in the tooth. LOL

 

I remember finding all kinds of great info here when I rebuilt my carbs a couple years ago. Though I don’t have the same model as you. The bench sync on the Mikuni carbs on my 85 xj700x the butterfly was set with a credit card.

 

Bike run's perfect off idle.
Look's like I will be taking the carburetors off.

 

-Does sound like “drop” related.

-carb could be oil-loaded

-first, im wondering if maybe a spring fell out from below the sync screw.

but then here’s a whole lot of thoughts, in no particular order.

-To re-set butterflies at bench-sync settings is near impossible without removing the rack. I’ve done it, but that’s with years of experience and the bike right here. the fact that it runs says the sync is close enough to dial back in.

-odd to have NO VACUUM even if the plug isn’t firing is a concern to me. Even with a dead plug there should still be vacuum and pressure by nature of piston/valve mechanics.

- how hard did it fall?
-could a valve be bent and open?
-could a piston have broken?
-Could the block have cracked?

- have you done a compression test? If there’s compression, there’s Almost got to be vacuum.

-could something be obstructing the exhaust pipe/muffler/airbox flow for #2?

- are you SURE there’s no vacuum? What if your gauge is bad?

I

 

Gauge is good.
Light drop, little damage ,sitting at a stop light and braced the fall with my body.
Broke the clutch lever, scratched the timing cover, lot's of oil into the air box.
Have good compression
If air was being restricted at idle going into # 2 I don't think you would have vacuum ?
It's getting air from the other cylinders for the good the compression reading if the # 2 intake air was restricted.

 

That’s why I’m wondering about a sync spring missing. It would potentially cause a butterfly not to open right—which would restrict airflow

 

Which would increase vacuum...
I don't have an answer, other than the vac port is blocked?
Try blowing down it.

 

Dave from Hogfiddles figured the issue out.
I removed the Carburetors and did a Bench Base Reset of the throttle butterfly's which Dave was kind and patience enough to guide me threw the procedure on the phone while was at lunch. Then reset with the sync gauges.
He is defiantly on my Christmas card list.
I would have been there a long... time without his expertise trying to sort this problem out.
So what was learned is to not mess around with those butterfly screws too much {point of no return} because inless you have a total understanding of how they work you will have a very hard time getting them correct again without doing a bench reset.
THANK YOU AGAIN DAVE

 

Nice work @hogfiddles !! Now go home. There is a package waiting for you.

 

My pleasure!

 

I have been trying to understand the theory or mechanics around this issue and can't seem to wrap my head around it.
To start I need to correct myself and say it that was cylinder #3 that wasn't getting vacuum at idle the reference cylinder for the butterfly's. Also my theory on compression testing was also incorrect in this case because motorcycles don't really have a intake manifold to draw air in from companion cinders.
The butterfly on #3 was only open a little the others were all closed, so I was getting vacuum on the measuring port 1,2and 4 and nothing on 3 ...so # 3 had too much much air flow causing the low vacuum I suppose.