XJ650 4th cylinder not as hot as other 3.

Hi all,
Just got my carbs back from a local legend,,have been cleaned and balanced.
Funny thing is even thought my XJ 650 4KO now runs well she doesnt seem to get as hot on cylinder 4..The one nearest my right knee. there is a spark though.
I havent owned an XJ before so have no clue whether or not she is down on power.
Any ideas before I go mad and start replacing CDI's and regulators.?
Had the oil replaced but the starter is now slipping.Not bad though as she starts handy.Will 20w/50 solve this.?
Thanking you all.
Morg.

 

# 4 on my 750 wasn't getting hot either. Turns out the intake manifold gasket - where the boot connects to the engine, was only half there, which let in air and made it run lean. Put a new gasket on it and it got hot instantly. Get some propane, WD 40, quick start, etc and with the engine running, spray around the carb boots. If the engine picks up speed, you've got an air leak. New gasket was $8.00, pretty easy job. If that doesn't solve the problem, you have to look at the carb again. Any backfiring at higher revs?

 

Thanks Dude,
Dont think there are any leaks in the gaskets.. i wonder if I fouled up the plug in #4.? Was running fine when I got the carbs back.
She did backfire a bit but seems to be ok now.
Am gona swap plugs in 3 and 4 and see if this sorts it.

 

The other thing I tried - to isolate the problem, was to get the bike running, then apply some choke, the good cylinders would start to stumble if the engine was hot, but the non firing cylinder got hot instantly. That isolated a lean running cylinder for me.