Help setting up new carbs...

I purchased a set of Mikuni BST34SS carbs off of ebay, from a 1989 Katana 1100.

These are 34mm flatslide CV carbs. I was used to my old mechanical slide carbs, so I am looking fro some insight into the problems I am having.

Setup:
77 1015 engine +1 intake valves, stock exhaust. Ports look to be as cast, but match the larger J model boots exactly.
Stock cams, 150psi cranking compression
Brand new J model boots and Pod filters
Dyna S igntion and coils
4 into 1 header with no baffle

Engine ran and started fine with the old carbs so it doesn't seem to be a mechanical/timing problem.

Carbs:
Mikuni BST 34 SS
132 main(possible dynojet stage 3 jet)
37.5 pilot fuel
135 pilot air
dynojet needle in 3rd slot from bottom
Checked the sync on the bench and all the butterfly's are open the same amount

Problems:

-Won't start cold even with full choke, without carb cleaner/starting fluid. Once it's warm it will fire right up no choke.

-Very touchy idle...Try to raise the idle...when I get to a certain point it just takes off to 2000...lower it and it drops to 1000. No in between.
Also if the idle is at a certain setting the RPM's will hang for a long time at 2000 after reving it, then drop back down to 1000.

This seems to happen when I turn the idle set screw far enough the the transfer/transition ports are uncovered in the carb throat.If I close it so it idles at 1K rpm I have to crank the pilot mixture screws out a lot...4+ turns, to get it to keep idling, and not well at that.

Should any of the transition ports be uncovered at idle? The carb has a total of 4 ports connected the the idle circuit. 1 way out in the throat that is always uncovered, and 3 in a tight group that get uncovered as you open the throttle.

-Starts popping and won't rev around 7K rpm under load...acting lean. I put 138 MJ in it but have not been able to ride it since. Trying to get it starting and idling dependably first.

I checked for vacuum leaks and there are none.

Any ideas on where to start?

tachrev wrote:

Engine ran and started fine with the old carbs so it doesn't seem to be a mechanical/timing problem.

Right, I would say its deffinately not an ignition/timing issue.

-Won't start cold even with full choke, without carb cleaner/starting fluid. Once it's warm it will fire right up no choke.

Sounds lean. After cranking, simply check plugs. If wet with gas, add air. If dry, add fuel Always works.

-Very touchy idle...Try to raise the idle...when I get to a certain point it just takes off to 2000...lower it and it drops to 1000. No in between.
Also if the idle is at a certain setting the RPM's will hang for a long time at 2000 after reving it, then drop back down to 1000.

CV carbs really have a tendency to do this because of the mixture ports in an out of tune condition, and when they're cold. The engine needs to be full hot (riden for some time) to aleviate the condition and find proper idle.

Should any of the transition ports be uncovered at idle?

Flow will be present even at idle. The butterfly gap should be about a 1/2 mm at idle (very little). Because of the shape and wear on the butterflys' a bench sync is barely adequate, and a proper vacuum sync must be done in order for them to work properly.

Trying to get it starting and idling dependably first.

Yup!
I would say go to 40 pilots at 2 turns out to start. The 138 mains might be ok.

MAKE SURE all float heights are EXACT. THIS IS CRITICAL.
They cannot be out of spec, or these CV carbs will not feed properly.

Hope this helps! Good luck.