TOPIC:

Hey guys, I got an 81 kz 440. The right hand cylinder starts up at approx. 3000 rpm and wont run at idle or anything lower unless the choke is on. It's got plenty of spark. I dont know a whole lot about multi-cylinder bike engines. Any ideas? Thanks, Max

pull carbs apart sounds like something is gunked up in there. goodluck,happy wrenching

thats what i was thinking, but i didn't want to face the harsh reality cause i absolutly HATE pulling the carbs out of that thing......how well does that carb cleaner additive or spray work? Any particular circut in the carb that you think is plugged up? I was thinking maybe the vaccum circuit for the slide valve. Maybe it takes about 3000 rpm before it finaly opens up?

I had a similar problem on my Yamaha, it happened to be the idler jet in the bottom bowl. There is a longer stem tube which goes into the carb and if that is clogged, it doesn't send any gas into the carb, hence when you put more throttle, the jet sends gas, while not idling. Just something to look at, it took me 2 weeks until someone told me that, ha. So hope it helps.

peachc has got it I think. Now I may be butchering every principle of carbueration because I am not an expert but I believe this problem is either an "idler" jet like peachc said or what is called the pilot jet which comes in at idle or lower RPMS right before around 3-3.5k RPM when it switches over to your main jet and then the cylinder starts to fire cause it is getting gas.

Hopefully this is just a matter of cleaning your pilot jet.

If wiredgeorge sees this he'll probably know exactly whats going on, just hold tight.

Cheers.

I have an 81 kz440 ltd and had a similar problem. The bike would idle up to 4000 rpm I would rev the engine up around 6000-7000rpm and release the throttle and it would idle back down to 1100rpm and slowly idle back up to 4000rpm. Come to find out it was the idle jet under the polyester plug; I could barley get my carburetor cleaner wire through it. I also rebuilt the carbs with a rebuild kit and recommend it!

Make a long story short, I have the bike back together and she purrs like a kitten!!!!!!!!!!

ah k, so its the low speed circuit. I was kinda leaning towards that, but just wanted to hear your guys opinion. Thanks, I will clean that and get back to guys
-Max

A lot of the times it can be the bowl which is clogged also and like said earlier, it is hard to get the cleaning wire into this area. i just let the bowl sit in chem-dip for about an hour and it cleared it right up, so just an option to avoid a wire in the finger as I first succeeded in doing. Best of Luck!

It's not RPM dependent, it's usually dependent on throttle position.

There are come carbs (called CV carbs, with squared tops) that open based on intake vacuum. The more air moving through them, the more they open to expose the larger jets. Most carbs are not the CV type, however, and expose jets based on how far the throttle is held open.

xr350guy,

If you're going to the trouble of pulling it apart, be sure to clean it all! Get yourself a bucket of carb dip -- you'll spend like $10-$15 -- and tear each carb apart individually. Remove all rubber and plastic pieces and soak the metal stuff overnight in the carb dip (it even comes with a dipping basket). Use cans of compressed air to be sure that the air passages are clear.

It's tempting, but don't use pieces of wire to chase the passages and jets, since you might end up widening a passage accidentally. Just use compressed air and carb cleaner, and go slowly.

oh yea, ive cleaned a few carbs in my time lol, but thanks for the tips...i'll be sure to try them. As for the cv carbs though, mine does have them and, well i think rpm does have alot to do with when the slides open. As you said, they open on intake vacuum, and if the bike is running at a higher rpm, theres going to be more air flowing through the carbs and intake, thus applying more vacuum to open the slides. right? because even if you open the throttle right up, and the engine doesn't rev up, the slides aren't going to open because there is not enough air moving through the intake to create the vacuum.

You got it. The CV carbs will open as far as engine vacuum dictates, and engine vacuum is regulated by RPM and throttle position.

Basically it's the smaller of the two -- if engine RPM is high, but the throttle is closed, then the slides won't open up far. If the engine RPM is low, but the throttle is open, they STILL won't open far. When the revs are high, and the throttle is open, well, then it's go-time!

The nice thing about CV carbs (as I understand it) is that they don't require synchronization.

It sounds like you've got a handle on things, though. Do let us know how it goes!

CV carbs definitely require synchronization.