Stuck at 4k rpm

Hey guys my 85' 750 starts and idles great. Give it slight throttle and it climbs to 4000 and won't come down. I've done a lot of research I don't think it's the boots leaking. And my timing advance (which I don't know much about) seems clean however there is no spring back mechinizm which I read about. I don't have the rubber bungs in my idle jet tubes. Could this be my issue? The bike was tampered with by the PO, has 3.75 idle jets 115 mains and pod filters. Any advice is welcome before I go buy a complete carb rebuild kit and blow that money.

Cables, stuck slides?
Steve

Cable is good, one of the slides isn't quite up to snuff the diaphragm isn't torn or have holes but isn't in quite as good a shape as the others.

What model 750? A GPZ? I've never heard of an " idle jet tube".

Edit: If you don't have plugs over the pilot jets you need them and a hanging idle is typically due to a vacuum leak.

Yes it's the pilot jet bung that I'm missing. My bad for the misinformation. I've tried the old wd40 vacuume leak test with no luck, the boots aren't new but I don't think they leak, do you think I should just spend the 60 and try new boots?

Just to rule out, is this with the choke on? 4k for a while till warm would be normal. If not you have an air leak somewhere. R

Am uncertain of the "bung" that's being referred to.
Here's a link to what's supposed to be the parts diagram of a stock carb on the 1985 KZ750 GPZ:

www.powersportswarehouse.com/p/Kawasaki#...0-A3-1985/080186C-10

This particular diagram doesn't show a plug for the pilot jet.

The pilot adjustment screw is shown as having an anti-tamper plug (which plugs are often removed and discarded by owners in order to easily access and adjust the pilot mixture.




As referenced by Nessism, the carbs at hand may be of the style that does have a plug or cap over the lower end of the pilot jet (not pilot screw).

If the carbs at hand are different from the carb shown in the above diagram, I'll defer to Nessism's expertise as to being a style that includes a plug or cap over the lower end of the pilot jet, in which event the cap or plug should be fitted (as shown below).



Good Fortune!

FWIW I have an '80 Yamaha XS 650 SG. It too uses the BS34. It does have a rubber plug covering the pilot jet, held in place by the float bowl. Without that plug in place, the bike won't run well. Mikes's XS has them I believe.

Thanks for all the responses, I'm thinking that my carbs are the type without the rubber plugs. I'm also thinking that my slide diaphragms may be the problem for my runaway idle. The diaphragms had some sticky substance on them which I cleaned off. My guess is that the PO put that on there as a ghetto way of sealing them better. After I removed it the idle became much worse. I'm ordering the JBM replacement diaphragms, any one have experience with them?

I do. They didn't seem to fit quite right. The thickness of what they refer to as the "donut" is narrower than the slot they fit into in the slides. As a result, it's possible to have a large (3mm-ish) variance depending on whether you bias them at the top of bottom of the slot (i believe I used the top). Nobody else seems to have this issue, so maybe I've got an oddball set of BS34s (possibly BS34SS).

I'm backpedaling a little here since the parts fishe doesn't show the pilot jet plug. I thought all BS CV Mikuni's used the plug. I suppose it's possible that the plug was discontinued, but there isn't any mention of that in the factory service manual.