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popping and backfire over 1/3 acceleration

4388 Views 7 Replies 5 Participants Last post by  Whiskey
I have a VL 1500 LC from '99. I've bought it last year in spring, run it out all year. There were some slight problems with the carburettors, sometimes no power and severe backfiring, other times no acceleration regardless how muck i turned the handle. So in this winter I took it apart. Dismantle completely the carbs, cleaned them, reset them to factory set up (3 turns out on pilot screw and 7 mm height an float.) then put them back, synchronise them. Changed the sparks with some k&n and air filter with performance K&N, the washable one. Had some small problems to decompression but after cleaning the coil and lube the cables and adjust the tension all good. It starts perfectly even in cold weather.
All done...let's test. Well the test was running perfect. Good response from acceleration, good tork and power. But when i accelerate above 1/3 disaster. It pops like a machine gun and the engine chocked. I almost hit the handlebar with my chest. I've tried to accelerate very slow, same. Until 1/3 of accel it runs perfect. After that it's a mess.
Pipes are drag with no muffler. No jetting to the carbs...
Have anyone some ideea? First thing in my mind was needle jet. But to rich or to lean?
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You are running an aftermarket air filter and aftermarket pipes and DID NOT rejet your carb?

You can't run that setup. Your bike is running dangerously lean. You MUST rejet the carbs to compensate for the additional volume of air.
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Thanks. Well actually aftermarket exhaust was when i bought it. The aftermarket filter i mounted it because it was kind of rich the mixture.
I,ll try to move the needle 2 shims out. If not i'll consider a rejet kit, but which one? Stage 1 should be ok?
Moving the needle won't make any difference. You're lean across the board. Both the pilot jet and the main jet need to be replaced. Yes, a stage 1 is the place to start, though that mean you will also need to figure out your needle height and how many turns on your a/f mix screw too. There is no such thing as free power...
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Thanks a lot Skrapiron. I'll give info in a week or two after rejet.
having the same thing with fully factory unit. Carbs rebult with factory carb parts. No differenct. [email protected]
having the same thing with fully factory unit. Carbs rebult with factory carb parts. No differenct.
Welcome, new member!

This post is 6 years old now. The person who started it has not been active on this forum for nearly as long, and so I doubt you'll hear from him/her/them.

You might want to start a new thread of your own to discuss the problem you are having. It would help others, to know, for example, what year of bike you have.

Also, spammers could take unfortunate advantage of your email address. You may want to reconsider posting it here publicly.
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having the same thing with fully factory unit. Carbs rebult with factory carb parts. No differenct. [email protected]
Welcome from Kennesaw GA!

You're welcome to start a new thread and get a bit more attention. Do you have aftermarket pipes by chance?
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