Total Rebuild KZ650 CSR

Guess you could say almost finished a total rebuild, free bike from a relative, sat for 7 years with gas and oil still in it. Have it at the starting point with the carbs pretty much rebuilt. when I start it now it will run ( choke in ) for about 30 seconds then starts to die out until it comepletly dies. Have the air screw turned out about 1.75 turns, floats are set to approx 18.5mm, 110 main jet ( which was origal size, but have 110.75 and 111 handy). Needle jets are set on the 4th rung which was what it was when I took out the original. I can throttle it up but seems to die out faster than if I let it idle. The only thing I have changed in the bike is that I went from the original exhaust to a 4 into 1. Being new to the bike, is there any advice or input that might get me on the road.

sounds like a fuel delivery issue to me. try running it on prime. another good way to test is while its dieing out while giving it gas, spray some carb cleaner in the intake and see if it takes off with that. was there any rust in the tank?

Also, when you pulled the carbs apart, did you pull the seats out too? those usually have filters in them and if theres a bunch of crap built up in there, it can cause alot of problems as far as sufficent fuel supply in the bowls.

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Hi, I also started to rebuilt a KZ650F2 (81) a month ago, still in the process of painstakingly strip each and every part, cleaning it, replacing rubbers etc etc..

What I know about the carb:
Originally the 81 KZ650 had a 102.5 Needle Jet and a 5CN16 Jet Needle (according to the repair manual/parts list). (although I also found an older one with 5CL16 needles)
The 110 jets you have are they original mikuni?
(should have this logo )
Because mikuni often has a lower jet value than the equivalent of other brands.
(so jumping from value a from brand a to value a+1 from value b gives strange results!)

Is the airbox original (no pods, no cut/saw off lid etc) are the air-hoses ok without vacuum leaks?
Check the rubbers (and those of the choke plunger also)for vacuum leaks with the gas of a small propane torch (without flame of-course), the engine will run faster if it sucks up gas through a vacuum leak.
Any vacuum leak will cause the engine to run horribly..
Replace those rubbers/hoses and start again..
(rinse and repeat.. )


The bleeding screw is set about right (manual gives a 1.5x as starting point)..

Only the jest you have are puzzling me: Mikuni goes in increments of 2.5 so you should have 110 ; 112.5 115 etc.. Though 110.75 and 111 are strange values, and most definitely not mikuni jets suited for this VM series carburetor.

Yeah guess I should have put the year. Its an 82, stock airbox. Just noticed a leak at one of the carb holders so am going to fix that asap.

Fixed the leak on the holders, 2 of them were put back on the wrong mounts. Fixed that. Put in the 115 main jets instead of the 110's and that seemed to make a world of difference. Still waiting on the new air filter so its airbox free right now. Does seem to sputter a bit after reving it up, could no air box attribute to that problem? Also when I do rev it up it stays at high revs until I block one of the intakes then it drops back down to 1000rpm. Any ideas? Still trying to find a vacuum gauge which is truning out to be a pain in the ass.

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