runs rich, occasional backfire thru carb,sounds like pinging in rear cyl : V-Twin Forum: Harley Davidson Forums

kickstartshovel · 08-12-2005, 08:22 PM

I have a 72 fx, fresh motor, 38mm bendix with an adjustable main, 1st. I was wondering if anyone had a starting point for the main jet adjustment , elevation here is 2500 ft.next is the motor runs exrtemely rich ,but I get a low speed to mid range backfire thru carb when she's warm. Finally I get a pinging noise in the rear cylinder at low speed, any help would be appreciated, I'm a fairly good tech but I think I need a fresh set of eyes on the problem , thanks for any suggestions

chopperb · 08-12-2005, 10:15 PM

check the timing and the plugs,wires and for at least 13.8 volts at the coil when running

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kickstartshovel · 08-12-2005, 11:14 PM

Thanks for the help bro,I'll let you know how it goes, Keep it on the wheels !

tequacha · 08-13-2005, 07:46 AM

what you running for a cam, what pipes?

kickstartshovel · 08-13-2005, 09:31 AM

andrews "J-grind" , dual exhaust, no crossover, thru 28" long FL style rocket mufflers

HDMD88 · 08-13-2005, 10:43 AM

Quote:

Originally Posted by kickstartshovel

I have a 72 fx, fresh motor, 38mm bendix with an adjustable main, 1st. I was wondering if anyone had a starting point for the main jet adjustment , elevation here is 2500 ft.next is the motor runs exrtemely rich ,but I get a low speed to mid range backfire thru carb when she's warm. Finally I get a pinging noise in the rear cylinder at low speed, any help would be appreciated, I'm a fairly good tech but I think I need a fresh set of eyes on the problem , thanks for any suggestions

The starting point on the adjustable main jet is 4 turns out....now thats going to be rich, to adjust it correctly the bike has to be at operating temp and in 2nd gear open the throttle wide open seee if the bike pulls good or breaks up. If it breaks up lean the jet by screwing it in 1/2 turn at a time and crank it open again in 2nd gear, continue this till the bike pulls smooth and strong. The timing has to be done correctly first. After you get the main jet done you can now adjust the idle mixture.
Doc

chopperb · 08-13-2005, 04:55 PM

Yeah what he said

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petelogan · 08-14-2005, 02:41 PM

What the Doc said, but backfiring in the carb indicates lean, while you also say rich at more open throttle. Pinging is obviously lean.

Sounds to me like you're lean on the idle and rich on the main.

I think I would make double sure the timing is spot on, and then look to the carb.

I ain't a pro, though.

Pete