my '53 chevy, with a 235 is backfiring and sputtering when i excellerate. i cant seem to be able to track down the problem, any ideas!??!?!! help!
Adjust the valves and the points gap first. Then start it up in the dark and see which spark plug wire is "leaking" sparks. Crhck the distributor cap for cracks or carbon "dirt" replace as needed. Bad plug wires will sometimes make an engine "chug" at what should be a constant speed.
Squirt some oil around the intake where it bolts to the head. Originally they had steel rings to locate the manifold. If they don't seat properly, you have a manifold leak. The oil, if you have a leak will be ****ed in and start to smoke out the exhaust pipe. The back firing sounds like the engine is running very lean. Ice man
How does it run at a say steady 35? Smooth ? If so and if backfireing through the carb that points to a lean mixture caused by the accelerator not doing it's job of providing extra fuel. with air filter off the carb and engine STOPPED look down carb intake with flashlight and work the throttle. Should see a stream of gas everytime you work the throttle.
ha, i just gave it a tune up, and it was running smooth then all the sudden..BANG! thanks for all the advice, ill try it out!
Check your firing order. Sometimes it is easy to get two plug wires switched and still have a reasonable sounding engine that will act funny when you drive it. About 30-something years ago I accidently switched a 1-5-3-6-2-4 firing order into a 1-3-5-6-2-4 after a tune up because I wasn't paying attention. It sounded ok at first, then acted low on power, then got worse after a couple test drives. I had one that acted a bit like yours when there was a loose wire connector under a nut and washer that wasn't tightened correctly. It would intermittenly lose fire for a very short instant then come back on again quickly. Another time it happened on a Jeep. The rubbing block on the points was worn (rusty spots on the cam) and letting the points gap get smaller and smaller. Once a loose condenser. Once, a wire on the points was rubbing ground inside the distributor every now and then, causing it to fire a plug at funny times.
alright, its not running as lean now which seems to have helped the backfiring but not all the way. and it still hesitates and has low power. i noticed that on the inside of the distributor cap there is what appears to be 'dust' from the connections where the rotor touches to send spark to the plugs, could they be too worn down?? i just got that cap a few months ago though...
You might want to double check that the spark fires at the right time when the rotor lines up with a cap terminal. I ran into one a long time ago in the 60's (autolite in a Nash maybe?)that used to fire when the rotor was between terminals. I am not sure what caused it, but we rigged it by rotating the cap and cutting a new notch in the distributor housing to make the cap terminals stay in line with the rotor. It could have been someone that took the dist apart and used a plate or points from something else, or a cap that looked the same but wasn't ... who knows. The phasing was way off. The point is that I have found similar misalignments in other distributors from Chevy and others, but none that bad. If you examine closely, you can sometimes find some distributors that will fire the coil when the rotor is before tha cap terminal or after the cap terminal by quite a bit sometimes. I think Dr Jacobs the ignition guy, calls it "indexing" the ignition when you fix that. I would be concerned by the light powder coating on the inside of the cap. It wouldn't take much atmospheric humidity or oil vapor to make it into a conductor for high voltage currents. You could have a spark that could be getting diverted by a conductive surface inside the cap. Clean it really well, or try a new cap. If you have parts inside the dist. such as brown advance weights, with a rusty brown finish, you could have an ample supply of conductive powder waiting for the chance to collect on the inside of the cap.
After reading the letter again, I thought of this... When you have something like dirt on the high-tension wires, oily cap surfaces, dirt on the coil, or things like weak wires, you could still have an engine that idles well, and runs well when demands are low. When you have a load on the engine, or wider throttle, the combustion pressure goes way up, the spark plug resistance goes way up. That is when the high voltage wants to follow the easier path. Long ago I had a Jeep that seemed like it would go through anything. I often brought it home so dirty you couldn't tell what color it was, even tho the paint was bright red. Never missed a beat on the trails. After I would clean it up, and drive it on the streets, even the slightest dampness or drizzle would make it stop in its tracks. No problem in the mud holes, it just couldn't drive across town. I found that even though the engine looked clean again, I was losing the spark through the plug wires. When I wiped down the cap inside and out, and then wiped the plug wires with a rag and paint thinner, it was good again until the next mud adventure. The only thing I could guess was that the local clay is so conductive that even thin residues you couldn't see, could divert the spark unless you got rid of every trace. It was strange, but wiping everything really well cured it. Mud, rinse, wipe, repeat...
Fuel pump. Even if it runs o.k. under accleration the pressure/volume may be so low that it runs lean. Mine did the same **** and it took a while for the pump to actually poop put.
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