carb tuning

[mnman]

hi guys, i hope you can help me. I'm currently working on an 81 CB 750 custom all stock. 4 in to 4 exhaust stock air box. it sat for approx a year and half not running. I pulled the carbs broke them all down, had them ultrasonic cleaned and reassembled them with all new parts from complete kit set. now I cant get it to idle. Ive checked for vacuum leaks and don't seem to find any. it is backfiring through the exhaust also. I will add that I had to replace the starter clutch, is it possible I might have gotten something back together incorrectly while doing the starter clutch? I cant even get it to run well enough to sync the carbs.
PLEASE HELP!

 

[mnman]

I'd like to add one thing, the bike has only 25xxx miles on it.

 

[Mista750]

How's your timing? You check timing using a test light without the motor running.

http://www.youtube.com/watch?v=0fkwDzu-ewY

 

[tommycarl]

You checked for "vacuum" leaks... is it safe to assume you mean you checked for leaks around the carb insulators and airbox boots to ensure that it's not sucking air? You're using a stock paper air filter, right? Have you completely assembled the airbox including the side covers and crankcase vent hoses? Did you bench sync the carbs before installing them?

 

[HEAD]

If you have not figured it out yet, Most likely the slow air jets are not clear. Its a very common problem on these carbs.