Runs Great under load - rough at cruise - Kawasaki Vulcan Forum : Vulcan Forums
 
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post #1 of 8 (permalink) Old 07-28-2019, 04:42 PM Thread Starter
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Runs Great under load - rough at cruise

1999 800 Classic runs great at idle and under acceleration, but when you back off of the throttle to maintain constant speed the engine runs rough. Just rebuilt the carburetor. The only thing I don't know if its set exactly right is the idle mixture screw. Previous owner had put this screw in without the spring. I put the spring back in, closed the screw and backed it out about 2.75 turns. Would this have anything to do with the way it runs at cruise? It idles great.

Thanks for any help
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post #2 of 8 (permalink) Old 07-28-2019, 07:17 PM
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Can you clarify what running rough means? Misfiring or popping from the exhaust? - Is the exhaust OEM and still baffled? Any mods done to the carb?

Floorboards are wear items. Scooterized, 52 pilot, 170 main and 3.25 turns out. 18/40 sprockets.
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post #3 of 8 (permalink) Old 07-28-2019, 07:28 PM Thread Starter
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Originally Posted by getdealtwith View Post
Can you clarify what running rough means? Misfiring or popping from the exhaust? - Is the exhaust OEM and still baffled? Any mods done to the carb?
Mostly misfiring. doesn't seem to be a lot of popping or backfire. I put a standard rebuild kit in the carb when I rebuilt it. It is running Vance and Hines Straight pipes. The best I can remember it ran fine when the pipes were first put on, but its been a while.
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post #4 of 8 (permalink) Old 07-28-2019, 07:43 PM
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OK, do you trust your rebuild and did the kit come with a float needle, as well? (Some don't). What jet sizes are you running and is your air intake modified in any way?

Floorboards are wear items. Scooterized, 52 pilot, 170 main and 3.25 turns out. 18/40 sprockets.
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post #5 of 8 (permalink) Old 07-28-2019, 07:55 PM Thread Starter
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yeah, I trust my rebuild. I've done carburetors before with success. I don't have much trouble doing the mechanical work on just about anything. The trouble shooting is my weakness. It did come with a float needle and the float was set midrange of the specifications. I am assuming I am running oem jets since that is what come in the kit. They looked the same as the ones I took out. No mods on the intake. The carb was taken apart and cleaned in an ultrasonic cleaner. as far as I could tell all passages were clean and all the parts cleaned up pretty good.
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post #6 of 8 (permalink) Old 07-28-2019, 08:18 PM
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OK, so let's assume you're running stock jets in a clean, working carb with open aftermarket pipes and an unknown spring in your mixture screw. The easiest place to start is to back it out 1/2 turn and test ride it. (Trying to diagnose anything mixture related by going in 1/4 turns, you'll go mad. That's only good for fine tuning later)

How does your air filter look like BTW? Stock or K&N? And how old is your petcock? These things can and will leak without you noticing and throw off your mixture, too. Our ethanol-y fuels chew up the older rubber bits just like they do in the carbs.

Floorboards are wear items. Scooterized, 52 pilot, 170 main and 3.25 turns out. 18/40 sprockets.
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post #7 of 8 (permalink) Old 07-28-2019, 08:28 PM Thread Starter
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I'll check the petcock. Right now I have it on an external tank. Air filter is clean and I think it is stock. I think you are right and the best thing to do is start with some adjustments and a ride. I'll try to get to that some time this week.
Thanks so much for your help. I'll post back what I find out.
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post #8 of 8 (permalink) Old 07-28-2019, 08:38 PM
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You bet. Check the spark plug for condition of the electrodes and the gap, too.

Floorboards are wear items. Scooterized, 52 pilot, 170 main and 3.25 turns out. 18/40 sprockets.
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