300 backfire

[killakobra]

i'm having some trouble with backfires in my 67. around 1800 RPM, even under even acceleration, it occasionally backfires. do you think this is a carb problem?

[f100x2]

Sounds like ignition timing to me. I would start their and see if it solves your problem.

[killakobra]

we have had the timing all over and it doesn't make much difference. just between 1800-2000 rpm I'll get the occasional backfire.

[HOWDY69]

Chilton recommends checking each spark plug individually by holding the spark plug 1/4 inch from a ground while cranking the engine.

4.1 Check for spark: Hold each spark plug wire approximately ¼ inch from ground with gloves or a heavy dry rag. Crank the engine and observe the spark.

[Ranchero50]

If it's a points distributor I'd suggest changing the points and condensor before playing with the carb if:

A. All the plugs look decent, no oil fouling or wet with fuel etc.

B. the plug wires are seperated and not arcing to metal or themselves somethere.

C. You don't see carbon tracking on the inside of the distributor cap or rotor.

D. if at 1800-2000 rpm you don't see droplets of fuel going down the venturis of the carb. If you do see them it could be a float or main jet issue.

Jamie

[killakobra]

it's got a duraspark setup on it so that rules out points. it's firing on all cylanders and the carb has been recently rebuilt.

[two-bit]

Maybe a vacuum leak????
Some of these things can be really aggravating to chase down.

Two-bit

[killakobra]

how would i check for leaks?

[Dragon]

Spray on carb cleaner spray the base of the carb and if the rPM changes you have a leak also all the vacuum hoses.