carb issue on kz400

i recently changed engines in my 76 kz400 and the new engine came with mikuni carbs that were off of a 650 suzuki, the previous owner of the carbs said they had a stage 3 jet kit in them, the bike idles fine, but wont go much higher than idle. there is no air leakage, cant seem to figure out why it surges/cuts out after idle, if you spray starter fluid into them you can ride around the block once or twice before the problem reoccurs, im thinking its a fuel issue but i dont know where to start any suggestions?

First thing I'd check is to make sure the slides are lifting when you pull the throttle.

Carbs that have vacuum operated slides are called CV (constant-velocity) carbs. I assume the Mikuni's are CV, but can't say for sure without seeing them.

The stock Keihin carbs (CV) have solid-piston slides. The Mikuni may have rubber diaphragm slides. The diaphragms are on top and they tend to get punctures or cracks over time. If so, the slides won't lift when you pull the throttle.

I assume you don't have the airbox if the you have a stage-3 kit. If you pull off the pod filters you should be able to see the slides if you look from behind the bike. DON'T LOOK CLOSELY! A BACKFIRE CAN SHOOT A FLAME 2 FEET OUT OF THE CARB. At 1/2 throttle, the slides should be all the way up.

Also, some types of pod filters can block the air ports at the throat of the carbs. Those must be open to get the slides to work correctly.

If the slides don't go up, take apart the tops and check the diaphragms.

the slides were operational, i thank you for that advice, i found the problem, actually both problems i had one was a clogged petcock the other was that in my haste to get it running after changing the engine i neglected the fact that my 2 air filters i installed were not on and it drew in too much air that way, once i unclogged the petcock and put new more restrictive filters on it it works like a charm