Backfiring

[gub]

Happens at idle and when getting off the throttle from 1800+ rpms.
When at idle, its louder when cold.

68' 289 motor. All ignition pieces not even a year old. Holley 600 cfm carb.

What could be the problem?

 

[CMYZ28]

backfiring through the carb?

 

[gub]

No, in the exhaust. I cant see anything coming out, i can only hear popping.

 

[Sean]

does it load up with fuel and smoke ?

 

[gub]

No but i can smell a raw fuel smell

 

[HardcoreB]

I believe you have an exhaust leak at the manifold.

 

[2004boss]

it might just be running rich or the timing is ra tard ded lol. should be easy to hear an exhaust leak at the manifold. take a look at the plugs should be able to tell if its rich or one isnt firing dumping fuel into the exhaust.

 

[gub]

Well it also doesnt run the best on nice days. When its warmed to operating temp and i shut it off, it has a hard time starting back up and once i do start it, it wants to shut off if i dont give it throttle.

 

[dave89iroc]

timing too far advanced?

 

[gub]

Last I checked, the timing was on right unless it somehow jumped? But i dont understand why it runs good on cooler 50 degreeish days but runs not as good on days like this.

 

[foxbodydave]

sounds like your carb is dumping too much fuel. how old is the car? pull out a plug and take a pic and post it up

 

[2004boss]

Last I checked, the timing was on right unless it somehow jumped? But i dont understand why it runs good on cooler 50 degreeish days but runs not as good on days like this.

the air is denser so more oxygen in the cyl= more power and will lean out the mixture slightly

 

[gub]

Ill pull a plug tomorrow, is there a plug that would show the best signs? The motor is 42 years old but its been rebuilt and the heads only have 5k miles on them along with the ignition pieces too.

 

[2004boss]

Ill pull a plug tomorrow, is there a plug that would show the best signs? The motor is 42 years old but its been rebuilt and the heads only have 5k miles on them along with the ignition pieces too.

if you have the time I would pull them all one at a time and have a good look, just to be sure ones not fouled

 

[gub]

Alright. Ill make time. But is there anything else it could be? Like, could 20 degrees will make that big of a difference?

 

[gub]

When i pulled the plugs, they didnt have gas or carbon build up on them. Could it maybe be running lean? On a holley 600 , which way are you sopposed to turn the idle mixture screws to add more fuel or air?