72' 350 5.7 Not Idling

[humbleabode]

Ok, ok, I'm a very novice truck person.


I have a 72 Chevy Truck with 5.7 liter engine. I bought it a few years ago and it ran well until last year. I was told that I needed to change my carb. I had a 1406 Edlebrock on it when I bought it and decided to get that one again.

After the install, she ran ok. I was hauling some dirt for a couple of days and she died. My mechanic changed the plugs, wires and distributor cap. All was well, until the belt wore off the alternator and she ran hot for a half a mile home. There the radiator spewed fluid. She turned over once long enough for me to park her in her place with a little white smoke coming out of the exhaust. There, after much frustration, she died. After the winter, I decided to spend some money to get her repaired. The mechanic said I needed a new radiator. I changed the radiator. She still wouldn't start. He thought it was bad gas. After changing the gas and the fuel filter, and adding seafoam, she still wouldn't start. I was told that the carb needed adjustment (Edlebrock). Bingo, she fired right up and held for a bit. After driving her for a couple of minutes she still wouldn't idle and drove erratically. The mechanic told me to put in high octane fuel (801). I added a full tank of gas, and the 801 and ran her for about 12 miles to work the old gas out. She still stalled, spurted and eventually backfired blowing the muffler wide open.

I called my mechanic who said the eldebrock was not the right carb and that I should get the factory model (Rochester). She still starts but does not hold an idle warm or cold.

Questions:

1. Did the high octane fuel blow my muffler
2. Can I use the Edlebrock 1409? That model worked fine for years. Why not now?
3. Could the high octane fuel be effecting my carb performance? Should I wait to burn that fuel up before investing in the Rochester and adjust the idle?
4. Is the blown muffler effecting my performance e.g. not enough back pressure?



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[Darkanion]

Questions:

1. Did the high octane fuel blow my muffler
2. Can I use the Edlebrock 1409? That model worked fine for years. Why not now?
3. Could the high octane fuel be effecting my carb performance? Should I wait to burn that fuel up before investing in the Rochester and adjust the idle?
4. Is the blown muffler effecting my performance e.g. not enough back pressure?

The muffler blowing open was probably caused because the carb was running rich (too much fuel for the amount of air the engine was getting). Over time, fuel accumulated in the muffler and eventually got hot enough to ignite, blowing the muffler open.

From what I'm seeing online, a 1409 is a "marine" carb. My inclination is to say if it worked before, it should still work now. But, not knowing the difference between a "marine" carb and a regular one..

Before replacing anything else, I'd say it sounds like the carb needs to be adjusted. When you get the mixture set right, it should smooth out, run better, and idle better, likely solving most of your issues with the carb.

The carb "may" be jetted too big. Years ago, I had a car with the Holley carb on it. The carb was designed for higher performance uses than *I* was using it for and was jetted real big. (Ran awesome, but got like 8 MPG on the highway. ) We eventually went through a bunch of sets of (smaller) jets to eventually get it jetted right so it would run when you stomped the go pedal, but got decent mileage when you weren't.

If your mechanic can't come up with some better solutions for you, maybe try a new mechanic?

Good luck!

 

[That Crazy Squirrel]

Backfiring is almost always an indication of incorrect timing. That, combined with the white smoke out the tailpipe that you observed, makes me wonder if you didn't maybe kill a valve or two running it hot like that, maybe even blew a head gasket. From what you described, forcing it to run when it was hot, I'm betting you cooked that motor pretty good, and I'd want to pull heads on it and check for valve and piston damage at this point.

 

[Darkanion]

Yeah, I forgot about the white smoke when I was writing my reply. The nut has a point or two in his post.

 

[Draenor]

Did you read the plugs to see if it is running rich/lean or burning coolant? Based off of that you can determine if you are jetted too big or small. Have you tried to adjust the idle screw or check timing? Can you perform a compression test to see if you blew a head gasket?

Since the overheating, you need to verify that the engine did not suffer any damage. After that you can start working on the idle and drivability.

 

[OldCracker29]

It looks like these guys already told you what I would have said. Good luck!

 

[Draenor]

Any luck?

 

[ScottyBoy]

I had an 87 Cutlass that I overheated once. I got it hot enough that it started blowing white smoke and sputtering and shaking. It never did run right after that. I took it to my mechanic who suspected bent valves. As soon as he removed the intake manifold, you could see several of the push rods were bent. So I obviously got the engine a lot hotter than I thought. Ended up needing a 3 angle valve job and new pushrods. I didn't have the cash to do anything with the bottom half of the engine, so I left it alone. About three years later, I lost compression on two cylinders because the rings failed. That's when I finally just replaced the engine.
I know that's not what you want to hear, but you need to pull the intake and see if overheating caused any mechanical damage, or else you will keep throwing parts at it until you are blue in the face, and have an empty wallet.