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It's possible you have a vaccum leak. With it idling spray some WD 40 around the rubber rings that connect the motor to the engine, also on any rubber hose (not tach cable ) heading into the engine. If the motor revs up, then you have a vaccum leak. If not you have the satisfaction of knowing there is no leak while you clean WD-40 off those areas (read- don't go crazy)

+1, vacuum leak.

You may want to try something other than WD40, WD40 is now made with a new formula that is hardly flammable and may not affect the RPMs like it should. Maybe carb cleaner instead. Don't let carb cleaner sit on painted parts.
What you're doing is filling any vacuum leaks where air is entering the system, with a flammable spray. When this spray burns it will change the RPMs and that is how you will know you have a vacuum leak.

Careful with those old rubber parts, they are often not made anymore. There are some long-term temporary fixes if you find cracked carb boots or carb holders.

No worries on the kz, check out kzrider for more suggestions and z1enterprises for plenty of replacement rubber parts!

You guys are freaking awesome....never did I expect to get this much help from total strangers with this bike.



Wish I could buy you all a drink that have chimed in on this one!!!!!!!!!

I learned to ride in San Jose when I was stationed in Monterey in the Army. Now I live in GA, but this summer I took my Kawasaki back to San Jose and went back to all those wonderful places where I learned to ride, and where you're going to learn to ride!
The CA climate is kind to old bikes and you found a good one. I'm glad to see anyone willing to keep the old iron on the road, they're still fun minus the payments and the computerized headaches!

coffee_brake wrote:+1, vacuum leak.

You may want to try something other than WD40, WD40 is now made with a new formula that is hardly flammable and may not affect the RPMs like it should. Maybe carb cleaner instead. Don't let carb cleaner sit on painted parts.
What you're doing is filling any vacuum leaks where air is entering the system, with a flammable spray. When this spray burns it will change the RPMs and that is how you will know you have a vacuum leak.

Careful with those old rubber parts, they are often not made anymore. There are some long-term temporary fixes if you find cracked carb boots or carb holders.

yep, that's a good place to start. If that pans out then you may need a valve adjustment. I had a similar problem with my 81 kz750. Had to set the idle speed high to keep it alive at stops, backfired when killing the engine or backing off the throttle at highway speeds and fuel consumption was higher than it should have been. Drove me nuts for a long time, ended up checking everything for vacuum leaks, pulled the carbs out several times to clean em, replaced gaskets, nothing worked. Turned out I had a few valves that were staying open due to no clearance. problem solved.....