Author Topic: backfire thru carb  (Read 444 times)

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Offline roadkingdresser

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backfire thru carb
« on: July 05, 2019, 02:04:19 PM »
hi guys. boy brought me an old 83 sporty today. said it started back firing thru the car all at once. sprayed sone wd40 in around the o-rings and the rubber where carb slides in. didn't seem to slow  the motor. about 1/4 of throttle it back fires alot. took the carb apart and everything looked ok. has origanal carb and exhaust,new plugs and lots of spark. any suggestions?
roadkingdresser

Offline Hossamania

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Re: backfire thru carb
« Reply #1 on: July 05, 2019, 04:52:13 PM »
Deleted. I had the wrong carb setup.
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Online Burnout

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Re: backfire thru carb
« Reply #2 on: July 05, 2019, 06:47:02 PM »
Check the spark timing on both cylinders?

If it is popping regularly/repeatedly maybe an intake valve not fully closing?
They don't call me Ironhead Rick just because I'm "hard headed"

Offline Tynker

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Re: backfire thru carb
« Reply #3 on: July 05, 2019, 07:22:28 PM »
hi guys. boy brought me an old 83 sporty today. said it started back firing thru the car all at once. sprayed sone wd40 in around the o-rings and the rubber where carb slides in. didn't seem to slow  the motor. about 1/4 of throttle it back fires alot. took the carb apart and everything looked ok. has origanal carb and exhaust,new plugs and lots of spark. any suggestions?

Take a close look at the diaphragm at the top of the carb. If it has a tear in it, it will do as you describe.
Earl "Tynker" Riviere

Offline Hossamania

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Re: backfire thru carb
« Reply #4 on: July 05, 2019, 07:43:55 PM »
hi guys. boy brought me an old 83 sporty today. said it started back firing thru the car all at once. sprayed sone wd40 in around the o-rings and the rubber where carb slides in. didn't seem to slow  the motor. about 1/4 of throttle it back fires alot. took the carb apart and everything looked ok. has origanal carb and exhaust,new plugs and lots of spark. any suggestions?

Take a close look at the diaphragm at the top of the carb. If it has a tear in it, it will do as you describe.

I thought of that too, but are these a CV carb on the old ironheads?
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Offline JW113

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Re: backfire thru carb
« Reply #5 on: July 06, 2019, 07:56:15 AM »
He said stock carb, meaning Keihin butterfly. But then says "rubber where carb slides in", meaning CV. I think some more detail is needed about the carb, as in what kind is it?

-JW
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Online Burnout

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Re: backfire thru carb
« Reply #6 on: July 06, 2019, 08:21:15 AM »
A punctured diaphram on a CV will not make it pop.
The slide just wont open and it won't make any power (probably rich too)

I assume the OP has already replaced the spark plugs with original heat range and not too big of a gap....
Good chance the plugs are black and furry.
They don't call me Ironhead Rick just because I'm "hard headed"

Offline roadkingdresser

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Re: backfire thru carb
« Reply #7 on: July 06, 2019, 11:01:54 AM »
It is a keihan carb and it does have rubber adaptor bolted to the intake. Good news is i found the problem,bad news took almost 10 hrs. put the plug testor for twin cam in and found out the coil was intermittently loosing power. one of the breakers under the seat a nut came loose. put a new nut on and O.K.
roadkingdresser

Online Burnout

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Re: backfire thru carb
« Reply #8 on: July 06, 2019, 12:22:45 PM »
That's a though one to find!

That will make some serious exhaust reports and other bad behavior.
They don't call me Ironhead Rick just because I'm "hard headed"

Offline roadkingdresser

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Re: backfire thru carb
« Reply #9 on: July 06, 2019, 01:24:29 PM »
Tell me about it.I'm sure I woke the neighbors up this morn. :gob:
roadkingdresser

Offline Panzer

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Re: backfire thru carb
« Reply #10 on: October 10, 2019, 06:34:15 PM »
 :hyst: :hyst:
You'll always be my best friend because you know to much.