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backfire thru carb

Started by roadkingdresser, July 05, 2019, 02:04:19 PM

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roadkingdresser

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

Hossamania

Deleted. I had the wrong carb setup.
If the government gives you everything you want,
it can take away everything you have.

Burnout

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"

Tynker

Quote from: roadkingdresser 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?

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

Hossamania

Quote from: Tynker on July 05, 2019, 07:22:28 PM
Quote from: roadkingdresser 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?

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?
If the government gives you everything you want,
it can take away everything you have.

JW113

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
2004 FLHRS   1977 FLH Shovelhead  1992 FLSTC
1945 Indian Chief   1978 XL Bobber

Burnout

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"

roadkingdresser

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

Burnout

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"

roadkingdresser

Tell me about it.I'm sure I woke the neighbors up this morn. :gob:
roadkingdresser

Panzer

Everyone wants to change the world but, no one wants to change the toilet paper.