i have a 1981 chevy malibu and it backfires threw the exhaust at high rpm, and also if i floor it and let go the car idles really low then cut’s off.
has new distributer and components, new spark plugs they dont need to be gapped. and new wires. i just found out i have a 1404 500cfm edelbrock carb dont no if its to small for my set up. i dont no the degree to set the timing i got it at 32 degrees. and the air fuel mixture screws are set to highest vacuum reading and out one hole turn from highest reading.
it has double rollor timing, comp cam 450 lift, hi rise intake, heads reserferce ported and polished, piston honed, new seals, HEI distributer, golmer belt drive, headers, single plain intake and tunnel ram. its a new style 350. Guy told me 383 stroker at first when i bout the car so not sure on that either , and i dont now the engine compression either. it has 3" dual exhoust flowmaster super 44 series
thanks again for any help in advance
You need an experienced mechanic to lay hands on this oldie.
Not much anyone can do over the internet.
[4/9/10] I really missed the mark on this one!
I hope you mean the advance is 32 degrees total with all the mechanical advance in i.e. max advance at 4000 rpm. If that 32 degrees is at idle you are also well overadvanced at high rpm.
What purpose do you use this car for? Is this a race car or a driver? If you intend to drive it on the street, it’s built all wrong.
First of all, how did you set the timing? Is 32 degrees the total advance (I hope so)? Try setting a baseline of about 8 degrees btdc at idle with the vacuum advance disconnected and plugged. This usually works well on a sbc. Also, check your mechanical advance springs and weights. This shouldn’t be a problem with a new distributor, but is worth checking into.
Also on ignition, it concerns me that you said the new plugs don’t need to be gapped. Any good spark plug needs to be gapped. The only plug I would ever run in a 350 is a copper core ACDelco. I’ve had good luck with R45’s gapped around .035 to .040.
Another thing to check is your cam timing. Many aftermarket timing sets have an adjustable cam gear, and if these are set up wrong, it can cause problems like this.
Your carburetor is not too small for your setup. If it is a drag car, you may get better performance out of a 650, but I wouldn’t go any bigger than that. If you drive the car on the street, I would lose the single plane tunnel ram setup, though. Those only work well for a drag car, running full throttle all the time. You may want to look into a jet kit and tuning guide from Edelbrock for that carburetor. I don’t have enough experience with those carbs to tell you how to set it up, but a little research and experimentation can result in great performance for the long run out of that carb.
Wow. This takes me back a few years. Is the 350 a factory original? They were quite rare in 1981. I owned an 81’ Malibu wagon with the 350 back then and my wife used to let me run it on the dragstrip at Warner-Robins. I also ran a 74 Vega GT with a 350 stuffed inside. I had a lot better luck with the Vega but that little Malibu wagon would run off and leave a lot of Mustangs and Camaros. Memories…memories.
Bolting a bunch of shiny, expensive parts on an engine does not always work out the way you hoped…
Caddyman…I may just have that engraved on a plaque and put upon the wall.
its 350 bored over 60 witch makes it a 360. i set the 32 degreese with a timing light and distributer unplugged, and idled it down after i was done. the spark plugs are Bosch-Platinum+4 / Spark Plug ungapable plugs. i want to be able to drive the car but at the same time get in it to. it has a transtec shift kit. ill try those plugs mentions. they recommended those plugs to me sense he didn’t no the gap.
When it comes to a modified engine the ignition timing is something that has to be tinkered with followed by regular inspection of the spark plug tips to make sure that you’re not getting into engine damage territory.
I have no idea what the timing should be set at on this one but I can tell you that 32 degree is going to be way too much and is flirting with engine damage. Total advance maybe, but not base timing at idle.
The backfiring and dying at idle could very well be a carburetion problem (jets and metering rods) but the ignition timing is the thing you should settle first; and do this before you do any highway driving. On the open road with too much advance and you can often kiss the engine top end goodbye.
I still have to reiterate, get rid of that tunnel ram and junk Bosch four prong plugs and put on a nice dual plane intake and a set of copper core Delco R45’s, get a tuning guide and jet kit for the carb, and set your base timing at a reasonable advance. A nice dual plane manifold will work great with that 500cfm Edelbrock. Also, check the springs and weights in your distributor. Some people put a too-light spring in there to get total advance early on, which is okay for drag racing but can really interfere with driving the car in any other way.
You didn’t mention the duration of the camshaft you have, but I speculate you have a HUGE camshaft in that car. This is not usually the best idea for a car you want to drive on the street. Bigger is not necessarily better for these kind of parts. Bigger cam is not always better. Bigger intake is not always better. Bigger carb is not always better.
It looks like you have a lot of money into the car at this point. It’s too bad you may have to redo a lot of it to get what you really want out of it…
Exacttly what else was done to the valvetrain? Unless other mods were made, that big cam is probably “floating” the valves at higher RPMs.
Another good point about the big cam, tsm. Most people can get much better performance out of a mild to moderate cam than out of a really radical one, especially if the car is to be driven on the street.
I talked to my father about the Edelbrock carburetor. He ran a lot of Carter AFB’s on a lot of Mopars in his day, so he is very familiar with the way they should be set up (Edelbrock carbs are exactly the same as the old Carter AFB). He said if you have a proper set of jets and metering rods in it for your motor, and the rest of the carb is in good shape and set up properly, a good starting point for your mix screws would be all the way in, then back out about a turn and a half. They shouldn’t have to go far from there, if anywhere. Hope this helps.
i got the car running better i re did the timing and changed out those bosch +4 spark. the car was idled to low. the vacuum guage stasy still now before it waved very fast. but i still have the one problem when i give it gas to fast from a stationary point it shuts off when i let off the peddle. and it still back fires to when im driving it and give it alot of gas.
It’s probably time to start in on that carburetor now.
i took the gas tank down too check for leaks and it had like 3 pin hole size leaks and another pin hole leak on the sending unit line,not the line attached to the unit but the line attaching the unit to the regular gas line i patched them up but am thinking of getting a new tank and sending unit. what effects would this cause