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Author Topic: back fire  (Read 4531 times)

Offline Schmitt20

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back fire
« on: May 03, 2010, 10:35:57 pm »
What causes the motor to back fire alot? Could it be a bad battery? At about 7,000 to 8,000 rpm it starts cutting out or popping alot, then when i let off it pops alot all the way down till 3,000 rpm.
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Online justfreaky

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Re: back fire
« Reply #1 on: May 03, 2010, 10:53:37 pm »
Not battery.
Timing, carbs, valves (need shimmed?), or hitting the rev limiter.
The backfire when you let off the gas is likely caused by raw fuel still in the pipes or header igniting from the heat.
My best guess FWIW.

Steve
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Offline VMS Motorsports

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Re: back fire
« Reply #2 on: May 04, 2010, 06:55:54 am »
Are you running you old carbs with your new motor?
Maybe something is set differently with the timing with the new one so you're not burning all the fuel?
Check valves, cam timing, carbs as Steve said.
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Online justfreaky

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Re: back fire
« Reply #3 on: May 04, 2010, 08:37:35 am »
Exchanged a few pm's with him last night.
Engine was just recently rebuilt; But carbs were not.

Steve
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