My 55 Chevy has started stalling and backfiring through the carb. I replaced the accelerator pump, but this did no good. Recently replaced the points with an Ignitor 2 and the proper coil, but the problem was present before the change. Seems down on power, not much oomph, (I know it never had a lot, but still...). Doesn't accelerate good, smooths out at speed, maybe is a little better after it warms up, but still pops when going from idle/low throttle to acceleration. I have to feather the gas to get it to go. This just came out of the blue. Any thoughts or direction to offer?
pull valve cover and make sure valves are operating paying close attention to exhaust valves as it sounds like bad cam lobe.
Do you actually get a squirt of fuel when the accel pump is actuated? Visual confirmation? It could be a plugged fuel passage between the plunger port and the.... squirt holes. I worked on one of these recently, it was all plugged up. The idle mix screw had zero effect, because the idle circuit was plugged too. The engine was so out of tune, timing, idle speed, it was all f'd up and it was a mix of "adjustments" that were collectively trying to make up for a plugged gunked up carb.
There is a similar thread going on recently. I had similar symptoms a few years ago and the culprit was a terrible intake/exhaust gasket. I vote vacuum leak. My intake /exhaust gasket was the thick one bought out of Oregon (hint) seemed to be made of paper and cracked after a few months, initially the first splits in the gasket were on the underside which led to a lot of misdiagnosis. HMMM, that's a good name for a Hot Rod, Miss Diagnosis Cheers, Cosmo in the '49
Like others said, check valves and gasket. Had a similar problem on a 54 engine, the valves needed adjustment. Yours should have hydraulic lifters if it's original engine. Posted using the Full Custom H.A.M.B. App!
This is a good place to start. The lean condition causes the backfire and the backfire causes more damage to the intake gaskets. Also the gasket between the intake and exhaust manifolds. Spray starting fluid, WD40 or water around the ports and see if the idle changes.
There are times that I wonder if anyone actually reads the posts before they offer a solution to the problem. I hope you find a solution to your problem, but I do tend to agree with a valve train problem! KK
Let me clarify; have you eliminated the ignition system as the possible cause? Have you re-installed the points system along with a known good condenser? It's POSSIBLE that the Igniter module is faulty, giving you the same symptoms. For those that like to read and not offer suggestions: it's just my suggestion to eliminate one variable.
Not sure how to tie this to your problem but last year on my 216 it backfired a couple of times thru the carb & the engine quit. It restarted & seemed ok but about 4 hours later the timing gears thrashed. Bad timing gears or gears going bad can cause bad valve & ignition timing every time it hicups. Jimmie
Ok - the popping/stalling issue was present before the Pertronix swap. I took the carb off yesterday and cleaned it, verified the accelerator pump was working. It is missing the check ball in the accelerator pump circuit, but again, the car ran fine without it. Took the rocker arm cover off and all valves are moving the same. It definitely gets a squirt when you accuate the throttle. I am beginning to suspect the vacuum advance canister. I sucked on the metal line and there was no resistance. Am going to check it out better today. Anybody know where I can find one?
Verify that the cam gear has not broken a tooth and / or jumped a tooth ..... or both. Crank gear is steel, but cam gear is Bakelite / Fiber. Not uncommon for Bakelite / Fiber gear to loose a tooth, knocking the cam timing out of kilter.
Poster stated "This just came out of the blue. Any thoughts or direction to offer?" 1. Drain oil, look for fiber fragments / pieces in oil. 2. Bring # 1 cylinder to TDC, then look at rotor position. 3. Pull timing cover.
here Concern here is that it happened all at once ..... a key factor in cam gear stripping out. Gear drive. Not an uncommon failure. Really bad when it happens at 60 MPH. Ouch ! Best scenario here is that problem is electrical and not gears. 1. If cam gear failed, it WILL show you fiber bits and chunks in oil. Easy enough to check with oil drain. Use a nylon or cheese cloth to filter drained oil. 2. If you see any bits & chunks, checking on TDC will tell you how far gear has jumped. Academic at this point. It'll have to come apart. 3. If # 1 and #2 are valid, doesn't matter how much of a bitch it is to get timing cover off .... it'll have to be done to get to chewed up gears. Replacing timing cover seal would be the right thing to do, as well, during the process. Optional cam gear was aluminum.
1. Check valve lash. Check them, don't just watch them move. 2. Check timing. With a timing light. 3. Check vacuum. With a gauge. 4. If it still runs like shit you might consider some of the more serious issues above. I wouldn't go pulling your cam out, and then later you find out it was just a valve or timing issue. Posted using the Full Custom H.A.M.B. App!
The Jalopy Journal
