I must be missing something

[Coronet 14]

72 Coronet 318 problem with back fire through carb at full throttle. Dosen't do it all the time. if you back out of throttle when it starts to sputter it won't back fire and will stay running. From a stop you can either take off or backfire and stall the engine. Before I put the electronic ignition in it wouldn't idle or even stay running. The carbs remanufactured. found vacuum leak at charcoal canister. Still intermittant backfire.

 

[WP29440SE]

what kind of carb? where is your timing set ? we need more info

a shot in the dark would say it is either dumping fuel , timing is wack , a stuck float , or you still have a vacuum leak...

 

[Coronet 14]

Carb is 2 barrel Carter. Timing is set at the line above 0 TDC on advance side. There are two zeros on advance side Timing is set on line between them. Thanks

 

[snakeoil24]

Back fire can be 3 things

1. Bad lean condition.
2. Stuck valve open.
3. Timing chain issue.
You need a vacuum gauge to determine cause.

 

[mark wickens]

Exhaust valve not opening enough...worn camshaft or lifter. Possibly collapsed lifter, bent pushrod. Usually the back fire is more consistent and severe with these issues. Pull valvecovers, pull coil wire off and crank over observing valvetrain movement. This is in addition to what was said above.

 

[cudajunction]

Im going with cam going flat...

 

[Musclecarmania]

What are you running for a coil? I've had this issue on my car.I tried everything mentioned,one day the fire just went out and it turned out to be my new Accel coil,I put the old coil back on and away she went,no more back fires or anything.Once I put everything else back that I changed she ran perfect....still is

 

[moparmarks]

Could be a lean condition. Easy check. While at an idle put your hand over the carb and try to choke it out. If the motor chokes and dies then move on. If it increases the idle then you have a lean and/or vac leak condition.

 

[Bruzilla]

Could also be your choke isn't working. Does this happen more when it's colder outside? I have a bad choke on my carb, and it backfires and stalls when the engine is cold, and will backfire at operating temps if the outside air is in the 50s or below.

 

[RustyRatRod]

If it's a cam lobe going out causing it to pop, it will have to be an exhaust lobe. But, the pop will be VERY repetitive...as in everytime that cylinder fires, because an exhaust valve staying closed will NOT make the engine skip, it will only blow exhaust back up through the intake and carburetor, causing the pop. An intake lobe gone bad will only make the engine skip. If it's not a repetitive pop, it's probably not a cam issue, so that might be good news. From your description, it sounds to me like it's running out of fuel and leaning out. Might check to see if the fuel filter is stopped up. I always check the cheapest things first.

 

[bm02tj]

It could be a bad check valve from air pump or EGR valve causing it to go lean
It could be crack in dist cap or plug wires leaking for cross fire

post cause as I am curious

Bruce

 

[Dennis H]

Exhaust valve not opening enough...worn camshaft or lifter. Possibly collapsed lifter, bent pushrod. Usually the back fire is more consistent and severe with these issues. Pull valvecovers, pull coil wire off and crank over observing valvetrain movement. This is in addition to what was said above.

For crisake, let's at least start with the easy stuff.

 

[caveman85635]

For crisake, let's at least start with the easy stuff.

Right. I'd start with checking the spark plugs. Maybe you will be able to tell which cylinder is popping. Mace certain none of the ceramics are cracked, which was the problem with my car once. Just a few weeks ago, my RR started backfiring a little bit, too. It turned out a spark plug wire end broke where the clip inside the boot gets folded 90 degrees. Put a new end on it and it's good...Plug wires arcing somewhere will make it backfire, too.

 

[Danomt]

72 Coronet 318 problem with back fire through carb at full throttle. Dosen't do it all the time. if you back out of throttle when it starts to sputter it won't back fire and will stay running. From a stop you can either take off or backfire and stall the engine. Before I put the electronic ignition in it wouldn't idle or even stay running. The carbs remanufactured. found vacuum leak at charcoal canister. Still intermittant backfire.

My take on this is probably fuel delevery, Pull fuel line and see if you get about an ounce per second. (normal)

 

[mark wickens]

The easy stuff should already have been looked at. The original post is very vague. As far as my post being way out there it's not. I had an RV brought to me last year by some backyard wrenches wanting me to put a carb on a 360 because it had an occasional backfire. After going through a laundry list of things incorrect it did have a worn camshaft. So the job went from a carb install to a cam swap. I am not saying this is the problem above but more info is needed.

 

[Coronet 14]

I'm going to look at it tomorrow. Had VA fix broken tooth. Mouth is very sore. Damn gobstoppers

 

[Propwash]

Went to the VA? Wow...you must have a lot of time to burn and are a brave fella...lol I would rather go to a voodoo witch doctor than the VA around here

 

[Coronet 14]

The three spark plugs are from right side. The single one is out of number 8 cylinder it's the worst one. Will do right side later.

Right. I'd start with checking the spark plugs. Maybe you will be able to tell which cylinder is popping. Mace certain none of the ceramics are cracked, which was the problem with my car once. Just a few weeks ago, my RR started backfiring a little bit, too. It turned out a spark plug wire end broke where the clip inside the boot gets folded 90 degrees. Put a new end on it and it's good...Plug wires arcing somewhere will make it backfire, too.