TOPIC:

First post on this Forum!
My name is Justin, I work in the USAF as Jet Engine Mechanic on the A-10. I have had a few bike;s but never one like this new TOY!!
I just picked up a 1983 KZ750L Other than i minor head gasket leak the bike has ran great. Compression is still between 120-130 on all four cylinders.
Now for the problem
The Po had installed pod filters on the bike but forgot to tighten the clamps. When i tightened them up i managed to knock the crabs out of there holders on the manifold. So i loosened all four clamps and re-installed the carbs and then the pod filters.

Upon first start the bike ran fine on choke but when i killed the choke the bike would drop in idle minimal throttle input it will rise and then drop but then slowly increase in RPM progressively getting faster and faster and never come down.

If i blip the throttle the RPM's stabilize at the highest throttle input and then continue to raise .
(VACUUM LEAK??)

I Found a cool trick that is much cleaner than Wd40 or brake clean, Propane!!! Sounds crazy but with a long hose i was able to get a spike in RPM at the #3 intake boot. I know have a new one on order after finding a small tear. But for now i tried high temp RTV but have had no luck.

I have never had a four Carb bike so this is definitely a learning experience. So my question is can i single vacuum leak like that force such a large problem?

Thanks for your time!

Yes, carb holders leaks can cause very bad idling and low rpm issues. I would suggest you just replace all 4 carb holders while you have the carbs off the bike. They develop very fine cracks on the surface that mates with the cylinder head. These cannot be seen with the holders on the head, but can and will affect idling. If one holder has a problem the others either already do to a lesser degree or soon will.

Take a look at the link below regarding the JIS (not Phillips) screws and using Kroil to break the bond between the screws and the cylinder head. Pay special attention to the first an last paragraph in the section titled "TOOLS." Quite a large number of folks have damaged the head by trying to remove the screws with the wrong bits, stripping them, then drilling into the head and messing it up trying to remove the broken screws. Other have broken the head by applying too much force trying to break the screws free. The link provides info on how to remove the screws with NOT problems at all. Ed

kzrider.com/forum/10-new-members/589649-...r-savannah-ga#594587

650ed thanks for the response! I just finished the removing and replacing the carbs again. Im getting good at it.
Anyways, this time i checked float levels and jetting just to see if there is any smoking gun in there. Everything i found was pretty uniform and in good working order. No change at all I have placed all four holders on order so they should be here this week.

I can see how these boots can and will cause idle problems however i can't wrap my head around how this can cause all four cylinders to take off to at least 6000 RPM without any kind of throttle input.

on your second paragraph you mention JIS screws. Where would these be located? on my carb boots they are all alan keys.

Thanks Again!

Air is leaking into the engine bypassing the throttle plates. A hanging idle and/or an idle that won't come down is the result. Replacing all the boots is the way to go. Silicone is a suckers bet and won't last.

Good luck

JRohrer wrote: 650ed thanks for the response! I just finished the removing and replacing the carbs again. Im getting good at it.
Anyways, this time i checked float levels and jetting just to see if there is any smoking gun in there. Everything i found was pretty uniform and in good working order. No change at all I have placed all four holders on order so they should be here this week.

I can see how these boots can and will cause idle problems however i can't wrap my head around how this can cause all four cylinders to take off to at least 6000 RPM without any kind of throttle input.

on your second paragraph you mention JIS screws. Where would these be located? on my carb boots they are all alan keys.

Thanks Again!

Somebody has been in there before you. The carb holders would have originally been fastened to the cylinder head with JIS screws (they look like Phillips but are too shallow for Phillips bits). Ed

I agree about RTV after i tried that i put on aviation permitex just for kicks it still didn't fix things. I have the shop manual in the mail as well but ii hate not being able to solve things. I guess ill have to just wait until i get the new seals and cross my fingers.

This bike has mikuni carbs is there a measurement for float valve level that i can check while i wait?

Thanks for the help!

Did the JIS screws have washers? Thinking more surface area to help squeeze.

The clear tube test must be used from the DRAIN function, and NOT from the "overflow" function.

Some carb designs have nipple from bottom of float bowl that serves dual purposes as both over-flow and drain. Clear tube may be simply attached onto the nipple (in "drain" mode, which generally means slightly loosened drain screw, whereas tight drain screw is "overflow" mode).



Where the carb has only the overflow circuit exiting through the nipple from bottom of float bowl, do NOT use the nipple for the clear tube test. Instead, use the hole where the drain screw threads into, as depicted in the follow illustration:





Good Fortune!

A clear plastic tube of the "correct" outside diameter may be self-threaded into the drain screw hole.

Properly done, it won't leak at all. However, minimal leakage won't invalidate the test.

The upside down dry measured float height is a default position to be fine tuned later when setting the actual fuel level via the clear tube method.

Because correct fuel level is the important objective, regardless of whatever float height is needed to achieve the correct fuel level.

Good Fortune!

Thank you if i get some time this week i plan on cleaning the carb's and doing this test. This sight rocks!

Would always first perform the clear tube test BEFORE adjusting the float height (bending the tang), because the fuel level may already be pretty close to spec (even though the measured default float height might seem out of range).

Ideally, the measured default float height is supposed to produce a fuel level that's within specs. But often this doesn't happen.

Good Fortune!

No, the carb holder screws didn't come with washers. The part they tighten to the cylinder head has metal imbedded in it; it isn't just rubber even though it looks like that.

Regarding the fuel level. As stated, use the clear tube method. It is the only way to accurately measure the level of the fuel in each carb bowl. The floats may not all have the exact same buoyancy, so setting float levels may only get you in the general ball park. When the carbs are off the bike, you can use the old carb holders mounted to a piece of plywood and set level to hold the carbs and do the clear tube test. Ed