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Doug E.
Doug E., Kawasaki Master Technician
Category: Motorcycle
Satisfied Customers: 2886
Experience:  Professional motorcycle mechanic since 1978. Vintage motorcycle restorer.
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Reg..Bike runs fine above 1/4 throttle, just slow speeds

Customer Question

I have a 1994 Kawasaki Vulcan 500 that runs rough at idle and at low speeds. Carbs have been cleaned, syncronized, new carb boots, floats adj to factory specs, new slow jets, new reg-rectifier(local dealer said this was the problem). Bike runs fine above 1/4 throttle, just slow speeds. Could it be the cam timing?? Valves have ben adjusted.
Submitted: 8 years ago.
Category: Motorcycle
Expert:  Doug E. replied 8 years ago.

If the cam timing was off it would have probably have bent a valve and it wouldn't be running right at all speeds. Being you have good compression I wouldn't suspect that the valves are bent.

Was the regulator replaced after the igniter was replaced? A bad regulator can damage the igniter. It's possible your ignition advancer isn't working (it's built into the igniter). I would have the timing checked with a timing light to verify that the timing is correct at all RPMs.

Does it make any difference how the mixture screws are adjusted?

Does the bike have any modifications? Is the intake and exhaust stock?

Do you have any idea when the problem started?

Customer: replied 8 years ago.
Hello Doug, yes the regulator was replaced after the igniter. The exhaust has been changed to a staggerd duel muffler on the Rt. side of bike. When I change the mixture screws, it does not seem to change it much. The intake is stock. When I talked to the lady I got it from, she said she had the igniter box and the flywheel replaced about a year ago at her local dealer.
Expert:  Doug E. replied 8 years ago.
If you put on the choke a little will it help the idle? Were any jetting changes made after putting on the pipes?

I would still check the timing to make sure the igniter didn't get damaged from the regulator being bad. Another possible problem might be the jetting being off due to the pipes. Check the plugs to see how they are burning and try putting on the choke just a touch to see if that changes how it runs. If the jetting is not correct to match the pipes, that would explain why turning the adjuster screws makes no difference.

I have to leave for a few hours. I will be back on later to assist you. Check the plugs and try using the choke and let me know what you find.

Doug E. and other Motorcycle Specialists are ready to help you
Customer: replied 8 years ago.
Hello Doug, well i checked the timing with my timing light, when it was running from idle to about 1/8 throttle I could not see the timing marks, they were jumping all around the viewport. When I opened it up to about 1/4 throttle, it smoothed out and you could see the flywheel advance like normal. I tried the choke and it didn't help. The main jets are 112, slow jets were #35, changed them to #40. Helped a little but still runs rough. Plugs are a bit dark with the larger jets on the slow side. I think you may have something on that igniter box. Thanks, Mark
Expert:  Doug E. replied 8 years ago.
Do you know anyone who can loan you an igniter to try?
Customer: replied 8 years ago.
No I don't. I'm going to call some salvage yards around here to see if they have a good one.
Expert:  Doug E. replied 8 years ago.
Before you spend any money try checking all of the grounds on the bike. You might also want to run the bike with a volt meter attached just to see if anything strange is happening when the bike is under 1/4 throttle.

Let me know what you find out.
Customer: replied 8 years ago.

Hello Doug, well I finally figured it out, the flywheel on the bike goes to an EX500 Ninja which uses a single pick-up coil. The Vulcan uses 2 pick-up coils. Found a correct flywheel and it runs perfect. Thanks for all your help.

Best Regards


Expert:  Doug E. replied 8 years ago.
Good job figuring out that one! That's not something you run across every day. Happy roads to you.