High revving when I pull in clutch and downshift (1980 KZ440)

Hi all,

I recently acquired a 1980 KZ440 with an issue.

First of all, getting the bike started requires a bit of choke and when it does start up, it idles at 4k. As it warms up, I am able to ease the choke down slowly until it's idling at 1.3k.

Gears 1 and 2 are kind of rough, but higher gears ride smoothly.

The main issue is when I pull in the clutch in and start to downshift when approaching a stop. When I pull the clutch in, it revs up to 4.5k and stays there until I am able to give it throttle and shift up after the stop.

I have checked intensely and failed to find any air leaks. I even replaced the carburetor boots as a precaution and tried all of the diagnostic tricks (wd40, ect). I also had the carbs synced, checked the valve clearances, and made sure all of the jets in the carburetor were clear.

Any ideas as to what is going on? Someone may have mentioned something about a throttle slide issue? I'm not sure what he meant though (I'm new to this)...

Thank you for your help!

Probably need to get the idle down to normal first

Check for a tight throttle cable. The throttle cable moves the throttle slides in the carb. The barrel looking pieces. You mention syncing them, did you take them apart or just sync them on the bike?

If it will not idle smoothly at the factory suggested rpm, there are likely carb issues.
Definitely tend to the cable maintenance. I use this-
www.rockymountainatvmc.com/parts/tusk-ca...-choice-cable-lube-p

While you are there, be sure there are no frayed threads. And that each cable moves like butter. Also check that the throttle tube rotates freely. It wouldn't hurt to take it off and clean the handlebar and the inside of the tube.

You may find this useful.

www.kzrider.com/modules/ServiceManuals/kz440.pdf

The throttle cable moves the throttle slides in the carb.

I don't believe 440s ever had slide carbs from the factory. They use CV carbs where the position of the slide is determined by vacuum through the venturi (which in turn is controlled by atmospheric pressure, RPM, throttle position, air density, etc.)

On my 440, if the throttle cable doesn't have 2-3 millimetres of play in the grip, the engine will rev way up when braking, especially during hard braking. It'll come down on its own after a few seconds.

1.3k RPM is on the high end of the spec; you should be able to get the idle to between 1.1-1.3k pretty well. And if the bike is running well, it should be able to idle at a bit under 1,000 without too much trouble, although it's better to keep the idle higher to ensure the engine has enough oil pressure. 4k with the choke on sounds high, but that might be due to a mis-adjusted fast-idle link. If it idles well warm with the choke off, I don't think that's indicating a carb issue.

Double check the points gap and the ignition timing, and that the advance mechanism rotates freely. My bike acted like it was running very lean with a high-hanging idle and poor running, and this issue drove me nuts for months before I discovered that the points had been neglected by the previous owner, and were barely opening at their widest. Getting that dialled in and re-setting the ignition timing made it run great.