New member Carb problem 1985 GPz 750 Mikuni bs34s

Hey, guys. New member here. I was told to come here with the problem I have from a member from another kawasaki forum. So here we go.

I bought this bike back in August of 2012. I have replaced a few things, spark plugs, plug wires, fresh oil and gas. I bought the bike non-running and had to change the starter motor clutch to get it started. I now have it started, but I have ran into a problem that I cannot figure out for the life of me.

The bike has K&N pod filters and a kerker 4-into-1 exhaust (I bought the bike with those mods) The bike will start and idle at ~1,100 rpm. The problem occurs when I give it a little throttle and raise the rpm to ~3,000 the rpms won't drop and slowly raise to ~4,200 rpm.

I dug into the carbs and cleaned them really well, discovered that the PO had also installed the dynojet stage 3 kit and also the diaphragm on the #2 carb was folded and allowed air to passby it. I have fixed the diaphragm, but the problem persists. I would love all the help I can get, no matter how simple the solution may sound, there is something I am overlooking.



I have also taken off the boots and inspected them, they look new. I applied a little gasket sealer and aplied a small amount of grease to the inside to seat the carbs. I also did a vacuum leak tests with the boots after I installed them with starter fluid. On the #2 carb the rpms raised maybe 150-200, but that could just be the starter fluid fumes being sucked into the filters. I have a video I took after the test.


(that smoke is just a little oil that I spilled on the exhaust)
At the end I'm fiddling with the idle screw to bring it WAY down and shut off all air flow.

I went and spoke to a pretty knowledgeable motorcycle mechanic today. He said it could be jetting. He gave me some 145 main jets to try. I did. Same problem.

Sounds like the bike is running lean, either the rubber manifolds are leaking or more like the CV carbs on that bike would rather have the airbox on instead of those pods

CV carbs and pods can be done they are just a pain to get right though

I wish the airbox and exhaust were original. I forgot to mention that the dynojet kit that was installed had 180 mains. I did research and found that dynojet and mikuni use diferent size charts and from what I can tell the dynojets are the equivalent of mikuni 168.8. so I dropped the richness about 24 sizes with the same problem.

Many of the stock diaghram style kawasaki carbs will have the rpms hang like that if there is a hole in the airbox boots or if the airboxor is missing. My 750 twin acted that way until i replaced the carb to airbox boots

Best you may be able to do without going back to stock: slide carbs from an earlier kz650 or 750 denser foam filters and tuning or, the airbox route.

Do You think I need to go richer on the pilot jets? The ones in there are the stock 37.5 size.