The Stovebolt Site Forums The Shop Area Engine Shop Backfiring Problem

My old 216 has developed a backfiring problem. Keep in mind that I have no idea of the engine’s history other that it is a ’48 not the original in my ’41. When I brought the truck home I disassembled, cleaned and reassembled the carb. Removed and cleaned out the gas tank, and completely replaced the fuel lines & filter. Changed the oil & filter. Installed new plugs, readjusted the points. That was about it. The engine started and seemed to run fine for 20 or so ½ mile trips around the block.

Recently I had the distributor out for a good cleaning and now that it is reinstalled the engine has developed the backfiring problem. It starts and idles fine, but has little power and as the RPM’s come up (maybe close to 2000) the engine begins a sporadic backfire right up through the carb. It almost seems like a sticking intake valve. However I’m not quite sure, as it did not do this before I removed the distributor and the fact that the backfiring seems to get worse as I adjust the distributor through its range of advance and retard. (Worse in the retarded position)

Any ideas ??

Has anyone experienced valve sticking with an old 216

Kip's41,

My obvious first guess would probably be your first thought too, maybe something you have already checked. This would be the firing order, which is 153624, clockwise from the front.

Other than this, it very well could be a sticking valve, or even a blown head gasket. I would verify the firing order and take a compression check. It might be worth your time to pull the valve cover and just take a look at the pushrods and general condition of things.

Stuart

Sounds like you may have the distributor a tooth off. Bring number one cylinder to top dead center and see where your rotor button is pointing. It should be to the number one plug wire in your distributor cap. If not remove and reposition.
It could also be 180 degrees off-you need to check it.
That sounds like the problem.
If all it is OK check the condensor and the coil.
Jeff

I agree with Jkane. I too think it's 180 deg. off, or at least a tooth or two off on the distributor. Take off the valve cover and crank the engine. When the intake valve on no. 1 cylinder closes, the very next time the timing pointer shows top dead center, that's TDC on the compression stroke on no. 1 cylinder. Your rotor should be pointing to no. 1 plug wire, or maybe the rotor will be a little bit after no. 1 if you have it advanced looking clockwise down at the distributor.

Kip,

Maybe the vacuum advance is not working properly (clogged line and/or port)?

I hope you do not mind my asking a general question (for anyone reading this) but I would like to learn something about sticking valves: how does a valve stick on a mechanical-lifter engine? Wouldn't that bend a push rod?

Tim

Kip's41,

Your engine will not run if it is 180&deg out. If you are a tooth off it is of no consequence, as turning the distributor as you have done will negate this problem.

Your truck idles fine, so all is almost well. When you bring the RPM's up, your problems start, or become noticeable.

If the valves were sticky/gummy from years of neglect or storage, this becomes problematic when the engine speed increases and the valve hangs OPEN, not closed. A valve that is varnished shut might bend a pushrod, but one that is sluggish to close will allow the firing cylinder to blast back through it and the carburetor. This is how I understand it.

Stuart

Stuart,

Thanks.

Tim

Ithink the dist. is a tooth off.

Kip's41,

I will modify my above post...if you have enough rotational movement of the distributor, you " should " be able to overcome being a tooth off on your distributor.

Stuart

Thanks all for the replies and advice. A couple if the things you guys have mentioned I had already tried and neglected to mention.

I have had the rocker arm cover off while the engine was idling and all valves and push rods seem to be about normal (Nothing not moving or bent). I have brought #1 up on the compression stroke (about 180 degrees of crank rotation after both valves have closed and their push rods spin freely). At this point the flywheel dot lines up with the pointer and the distributor rotor lines up with #1 spark terminal. Also sure I have the firing order correct 15 to young, 36 to old, 24 just right (I was younger when I memorized it). I have had it running for about an hour while dinking around with the distributor trying to make the problem go away and have seen no evidence if a head gasket leak or of a cracked head. (No bubbles in the rad no coolant leaks and no discoloration in the oil)

The odd thing is that the engine starts and idles fine (I don’t think it would even run with the timing off 180, or even one tooth). The backfiring is NOT at a set frequency.

I’m beginning to like the suggestion to check the condenser. And ordered all new ignition stuff this AM (cap, wires, rotor, points & condenser) I’ll post the results here or be back for more advice.

Thanks again

If you had the dizzy out for a good cleaning you might have cleaned some of the dwell out of the points. Points a little to close or to wide will cause problems as the rpms go up. Check the condenser and the point gap.