1981 Elco 305 - 2 cylinders not firing

[RustBucket]

how many miles on the engine?

i have no idea. ive only had the car going on 2 years and the previous owner did not know.

Does it pop through the carb when you rev the engine in park or neutral?

it does not pop while in park. i havent tried in neutral.

after performing a compression test, and finding low compression. the next step in diagnosing your concern is to perform a cylinder leak down test to determine where the compression is going.
popping back through the carb usually indicates valve train issues, burned valves, sticky valve stems or lifters. while flat cam would give low compression, it would not cause popping back.
mmo or gm crank case cleaner may clean up the rings and give better compression, it would not address the popping back. it may help with sticking lifters depending on where the lifters are sticking.
adding zinc at this point would be a waste of money.

i added half a can of seafoam to the carb while at high rpms. shut the engine off for 10 minutes then turned it back on and reved the engine up again until smoke stopped. i can now floor it even more before carb starts popping. it got better. i'll run another compression test in a bit. waiting for car too cool down so i dont burn myself up trying to get the #7 plug out lol.

fellas, this car is a hoopty put together with junkyard parts. im not afraid to try some weird stuff to it, long as im not throwing crazy money at it. thanks.

 

[pontiacgp]

on the bad cyinders remove the plugs and pump air into the cylinder, with the valve covers removed you'll hear the air escaping the valve if it 's a valve or you'll hear the air escaping the crankcase if it's rings

 

[RustBucket]

on the bad cyinders remove the plugs and pump air into the cylinder, with the valve covers removed you'll hear the air escaping the valve if it 's a valve or you'll hear the air escaping the crankcase if it's rings

I didn't know i had to remove the valve cover. I removed the oil cap and tried to hear from there. I don't know exactly what air running through the engine sounds like but if i had to guess it sounded like air was filling in the oil pan. I dont know how far up or down my piston was prior to doing this (if that even matters)

 

[Bonnewagon]

How old is the gas? Stale gas gums up the valves and causes backfires. Ask me how I know.....

 

[RustBucket]

How old is the gas? Stale gas gums up the valves and causes backfires. Ask me how I know.....

Gas is new. Just topped off last week. Regular unleaded. I really have no clue how the previous owner had this car. He had it parked when i bought it. He thought his transmission went out so i had it towed to my place. After checking it out i found the transmission lines were busted. Always ran like crap since i got it.

 

[roger1]

Sounds like you’re not running zinc in your oil and the camshaft went bye-bye

I think there's a high chance that is what the problem is.

Doesn't even necessarily mean he was running oil without zinc either. This was a common occurance even before they removed the zinc from oil.

 

[pontiacgp]

wiped cam lobs will not cause a cylinder to loose compression

 

[roger1]

wiped cam lobs will not cause a cylinder to loose compression

If it's the intake lobe it certainly would.

 

[pontiacgp]

If it's the intake lobe it certainly would.

not with a static compression test unless the lobe is completely gone

 

[roger1]

not with a static compression test unless the lobe is completely gone

That's what they do when they go. Once the lifter galls, it takes the lobe all the way down very quickly.