Kawasaki GPz550 Carburetor Troubles

| 10/22/2019 10:01:00 AM

Motorcycle Classics tech expert Keith Fellenstein
Editor’s note: If you’re having trouble with that old Suzuki, BSA or BMW, Keith Fellenstein is your guy. From motorcycle tuning tips to detailed motorcycle engine repair, he can draw from a wealth of experience to help guide you to success. Send questions to: Keith’s Garage, Motorcycle Classics, 1503 SW 42nd St., Topeka, KS 66609, or send an email with “Keith’s Garage” as the subject.

Q: Before I shove this bike off a tall cliff, I figured I should ping you on your vast experience! I’m working on a 1982 GPz550 which is close to complete, except that I can’t seem to be able to sort out a carburetor issue. It has the dreaded TK CV carbs. I have been through the carbs too many times already and all jets are clear, passages flow carb cleaner and air, float levels checked.

It has pod filters and an aftermarket 4-into-1 exhaust (I wish it had the standard exhaust, but that is the way it came). I have a Dynatek Stage 3 ignition. I have a 1983 GPz550 which runs great, and I set these carbs up using that bike’s setup as a starting point.
It has new plugs, wires, and I changed the igniter with a spare I have.

The bike starts easily (too easily, actually) and will run at lower engine speeds, but begins to die when you open the throttle, and will spit and buck when you close the throttle. Initially it felt like a lean condition, except that the plugs came out black and sooty — classic rich condition.

I have the slide needles in the leanest position, but nothing seems to make any difference. No amount of changing jets or adjustments appears to make any difference.
I did notice that if I manually hold open two of the slides (need the other hand for the throttle!) it seems to clear out and rev more cleanly. It almost seems like the slides aren’t opening quickly enough to flow the necessary air.

The diaphragms appear good and the slides do lift with the throttle. I’m wondering if the needle jets need to be a leaner size, or am I missing something else I should be looking into? Any thoughts would be appreciated — that cliff is moving closer and closer! Thanks!

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