Question about KZ carburetors
 

This is a copy of the message I posted on the KZ owner's forum.

I also wanted to post it here to get your input as well. The bike runs GREAT. I have about 500 miles on it, but I'm having a problem synchronizing the carbs...

Good morning guys.

My name is Bill. I'm a doctor in the Southeast Washington desert. My hobby is car and motorcycle restoration.

I am in the process of saving an old KZ I picked up for almost free. It was abandoned at my friends motorcycle shop when he told the owner it would cost more to fix than it was worth. I got it for a couple hundred dollars.

I had it running in about 1/2 hour.

It needed a battery, carb holders (those were a PIA but I've got it sorted), fork seals, and some small miscellaneous stuff like chain adjustment and spark plugs. The paint and chrome and seat are in near perfect condition. Not quite a 'showbike' but an excellent example nonetheless.

Here's my problem. I have used the search function and did not get an answer:

The idle will not go low enough unless the carbs are out of synch.

I have no vacuum leaks. The throttle cables have enough slack in them. The linkage is free, clean, and oiled. The valves are adjusted, compression is fine. The bike has 6,500 miles on it.

It runs great, but is dodgy when cold for the first 1/2 mile after startup.

Top speed on level ground, in a tuck, is about 85 which seems low to me, telling me there is still something wrong, i.e. carb synchronization.

The idle adjuster is backed out all the way. The fast idle cam is not holding the throttle open. The carbs have been cleaned, new diaphragms and float needle valves fitted.

If the carbs are in synch, she will not idle below 4,000. The only way the bike is ridable is if I deliberately mis set the synch about 2 cm Hg. Then it will idle at 1,200 or so, and fairly smoothly. I think this is because one cylinder is getting too much mixture and driving/being slowed by the other one which is getting too little.

I hope this makes sense.

So, even with the idle screw backed out all the way, she still wants to idle at 4,000.

Please help me guys. I'm bright enough and can't figure this one out.

I really enjoy this bike, and she looks and runs great, but I know she can be better. I'm a perfectionist and I know there is something wrong her.

Bill

Doc,
I'm making the assumption that you pulled the carbs and cleaned them with the following questions;

Are the butterflies back into the original throats?
If they are back in the original throats are they seated right to close all the way?
Did you bench sinc the carbs before re-installing?

I had the same problem with the carbs on my V4. I didn't bench sinc them before re-installing or I would have found that one of the butterflies was not aligned correctly in the throat.

I just cleaned the jets and bowls etc. I changed the float needles and the bowl gaskets. I've been thinking about your thought. Wouldn't the synch adjustment between the carbs compensate for such an issue?

Would this maybe explain why the stop on the throttle never rotates all the way back to the idle stop screw?

I'm thinking of either liveing with it or sending the carbs to some expert somewhere. It's hard for me to live with such studd. I'm an OCD perfectionist. :(

That's the problem I had. It would idle too high until I twisted the throttle away from me (two cable system). I had to pull the carbs again (four in the rack!) and when I checked I found that one of the butterflies was sticking but could be forced closed by twisting the cam. I looked around the edge of the butterfly and, sure enough, I could see daylight though. I loosen the screws and it snapped into place. I was then able to bench sync them before re-installing. I synced them again with my homemade manometer and it runs great now.

Can you see down the throats to see if the flies are closing all the way?

I bet that's it. I'll have to pull them, again, and check it out. I won't have a chance until next week. Atay tuned. :?

UPDATE. Could not get bike started today to come to work. I'm gonna have to pull the carbs again to sort this one out. Cold starts had been a bit difficult, but I overlooked it because it was OK when warm. It isn't right...

The problem was not the butterflies. Tomorrow I'll (re)check the float levels...

By far no mechanical expert, but do the carbs have diaphragms? Maybe one has a pinhole.

Allen

Yes they have diaphrams, and they are in good shape. Also the diaphrams are not active at idle speed so not likely part of the problem, but it was something I considered.

I'll dive into them again tonight...

How does the choke work on those? Is is a butterfly or the enrichener type? If the enrichener maybe one is sticking?

I am just guessing here.

Butterfly on this model. It is another problem area as it does not close all the way, about 75%. This is probably why it did not start yesterday AM.

Thank God I think it's fixed, again.

The starting problem was related to the choke linkage, not allowing the choke to close. I adjusted it.

The fuel level in the right side carb was too high, I reset that. Then I synched the carbs, again, set the idle, and turned the pilot screws each in 1/2 turn.

Seems OK. :D

She started right up and ran fine this AM.

Top speed level ground, in a tuck on the tank, after a long streach is 90 MPH. I bet that means the bike is working normally.

I'm declaring victory and I'm not going to fix anything else! :D

Congrats. :)

90 MPH on a 33 year old bike! You're one brave hombre. 8)