'81 CB 750 backfires btwn 3000-4500 RPM's

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Billc51 · #1 Post by **Billc51** » Sun Jun 11, 2006 8:28 am

Hi All,

My 750 custom is backfiring between 3000 & 4500 rpm's. I've replaced the plugs, plug wires, the coils and most recently the CDI spark units. I thought it was electrical however none of the replacement parts has helped.

I cleaned the carbs last fall '05, Could it be they are out of sync?

Any suggestions?

Thanks,

Billc

DivideOverflow · #2 Post by **DivideOverflow** » Sun Jun 11, 2006 8:38 am

I would definitely try synching them. Also, my friend's bike got a backfire from excessive richness in a certain RPM range (when decelerating). He adjusted his mixture and it went away.

Billc51 · #3 Post by **Billc51** » Mon Jun 12, 2006 10:39 am

thanks for the response.

I synced the carbs and the same condition exists.

Any other ideas?

MontyCarlo · #4 Post by **MontyCarlo** » Mon Jun 12, 2006 12:37 pm

Exhaust leaks can sometimes cause backfiring from air entering and igniting unburned fuel. Check for leaks at all the joints.