KZ400, one carb running rich, fouling plug.

I have a '75 KZ400D, we've pulled the carbs, put in new rebuild kits, cleaned everything, and been thru them about 3 or 4 times as we've been battling a running problem with the bike. Seems like the left side carb is running rich, fouls a plug after only 5 minutes of running/riding. Pull the plug and it's wet, stick in a new one and left side cylinder comes back to life, smokes from the exhaust. We've got the air mixture screw turned out 1.5 turns and tried at 1.25 turns out and makes no difference. Is there anything else I should be looking at?

Needle and seat leaking?
Float set to high?

Did you install new inlet valve needles and seats?

I would definitely check the fuel levels in the bowls with a clear tube and adjust as necessary.

Kymasabe wrote: I have a '75 KZ400D, we've pulled the carbs, put in new rebuild kits, cleaned everything, and been thru them about 3 or 4 times as we've been battling a running problem with the bike. Seems like the left side carb is running rich, fouls a plug after only 5 minutes of running/riding. Pull the plug and it's wet, stick in a new one and left side cylinder comes back to life, smokes from the exhaust. We've got the air mixture screw turned out 1.5 turns and tried at 1.25 turns out and makes no difference. Is there anything else I should be looking at?

If everything seems to check out ok with the carb, the next simple check would be a compression check. If you have low compression in that one cyl this will cause a "rich" condition.

Kymasabe wrote: I have a '75 KZ400D, we've pulled the carbs, put in new rebuild kits, cleaned everything, and been thru them about 3 or 4 times as we've been battling a running problem with the bike. Seems like the left side carb is running rich, fouls a plug after only 5 minutes of running/riding. Pull the plug and it's wet, stick in a new one and left side cylinder comes back to life, smokes from the exhaust. We've got the air mixture screw turned out 1.5 turns and tried at 1.25 turns out and makes no difference. Is there anything else I should be looking at?

I've been working on getting my 400 to run right for a few months now. If you had the mixture screw at 1.5 turns and it was rich, 1.25 turns would be MORE rich. In is rich, out is lean.

At least from my experience and understanding. As you turn it out, you are letting more air into the air/fuel mixture.

Nebr_Rex wrote: ...Float set to high?

Agreed.

If not already done, would perform the clear tube test to assure fuel levels are within specs.

A too high fuel level can result in an excessively rich mixture, regardless of carb settings being otherwise correct.

Good Fortune!

First step is to verify fuel level (as was mentioned).

Second is to verify the jet plug is installed and sealing properly. This is critical on those early Keihins. It's the littl eblack rubber plug that gets held in by the little metal bracket in the float bowl. If it doesn't seal, you get too much fuel.

wouldn't it just overflow? or would it run rich without overflowing?

Tmiron wrote: wouldn't it just overflow? or would it run rich without overflowing?

If the fuel level is too high, the mixture will be rich. It will not overflow unless the level is ridiculously high or the float valve is not seating properly.

If the rubber plugs are missing, it will run rich, but not be overflowing. The rubber plugs do not affect fuel level. They affect flow through the jets.

The fuel float valves control fuel height.

Both need to work properly.

Kymasabe wrote: I have a '75 KZ400D, we've pulled the carbs, put in new rebuild kits, cleaned everything, and been thru them about 3 or 4 times as we've been battling a running problem with the bike. Seems like the left side carb is running rich, fouls a plug after only 5 minutes of running/riding. Pull the plug and it's wet, stick in a new one and left side cylinder comes back to life, smokes from the exhaust.

What color is the smoke?

blue = burning oil
black = too much fuel/too rich