Chevy 350 starts but runs horrible HELP!!!

inforcer958 · #1 09-21-2007, 08:03 PM

I have a 1985 chevy el camino.. it had a 305 in it. at the beggiing of this summer i replaced that 305 with a 350 sbc. I have an edelbrock intake and carb on it. I don't run emissions at all. Full length headers back to dual glasspack mufflers.... tranny seems fine.. replaced all seals when i re did the motor...

The car starts up fine (sometimes), then it revs up to a little higher than normal RPM.... it ussualy stays running but the idle is very very sporatic... it goes up/down about 200-300 rpm... starts from about 1000, and goes anywhere from.....900-1300, then when i put it in and drive gear it drops heaviley torwards 500.... i have opened up the carb and cleaned everything out.... i have looked and i kno the engine by heart..... there are no loose plugs or vacuum lines... i have changed the fuel pump.... the soft fuel lines fron the tank to the pump and the pump to the carb..... i have also dropped the gas tank and checked all the pick-up and sending unit....

The idle is a problem... but the main problem is when i do get it on a good day and it runs for me.... when i get it on the road it seems to act well. but then boggs and seems to just chug down the road... having no acceleration... the engine doesn't die on me....then i let go of the gas and it seems to come back to it running smoothy but just at coast.... and even the power lose problem is sporatic....

DOES ANYONE HAVE ANY IDEAS? lol Anything would be appreciated. thanks

777stickman · #2 09-21-2007, 08:42 PM

Ask around and see if you can swap carbs with some of your buddies. If you have the "performer" (not the RPM) manifold you will need a "spread bore" carb. This is the 1st thing I would try to start eliminating things.

Your problem, as described, sounds like a vacuum leak. But you say that you've checked everything. Have you sprayed carb or brake cleaner around the carb base and around the intake with the engine running? If you have a vacuum leak the spray will make the motor either speed up or slow down.

SpinnerCee · #3 09-21-2007, 09:10 PM

Seems like you're used to EFI and a computer controlled engine management -- a carb is not like that -- it will run differently when cold vs hot and when the weather changes -- not a problem, just the way it works -- expect to tune the carb frequently.

Another issue may be components that are mis-matched -- ie. too much carb for the cam in the engine -- also make sure you have what you need to tune the carb -- you'll only get so far making idle speed adjustments alone -- static ignition timing, and distributor advance curves play a huge role in tuning a non-computer controlled engine.

inforcer958 · #4 09-21-2007, 10:37 PM

Thanks for all those comments...

Now someone told me that i might need to get the carb rebuilt.... would that make much of a difference? like i stated i opened it all up and cleaned everything... looked to make sure the metering rods and the idle sets and all that weren't grooved or worn down... i am hesitant to put out 150$ to have someone else do it.... or even the 40$ to get the kit and me do it if it isn't the problem...

inforcer958 · #5 09-26-2007, 04:33 PM

Well i did alot more tinkering under the car and i found that the hard fuel line had a crack in it... and was sucking in awhole lot of air with the fuel... causeing the pressure to be horrible. It runs alot better now but i still need to fix the timing i think... now it starts fine.. runs at a constant RPM, when i put it in gear it doesn't flutter or anything... the main thing is that when i get going it seems like when i give it a good foot... the extra gas doesn't help it to accelerate any better. I lay-off a little and then it seems to accelerate better with more gas... is the timing too advanced or too retard? i have a vaccuum advance on it hooked up to ported vaccuum on the edelbrock carb... Any help would be great.

777stickman · #6 09-26-2007, 06:26 PM

Is your Edlebrock carb a Quadrajet clone? If so the secondary air valve is opening too soon.

67chevypickup · #7 09-27-2007, 06:52 PM

it does sound like your timing could be too advanced try to retard the timing 2-4 degrees for the hell of it, it could make a world of a difference

Torch · #8 10-02-2007, 11:15 PM

Almost sounds like it is getting too much gas into the engine, do you have obvious black smoke coming out of the tail pipe and have black soot all over everything around the tail pipe?

Do you hear the engine pinging when you try to floor it?

Could be a problem with the vacuum advance, your static timing should be 4 or 8 degrees (from what I remember), what is your timing set at?

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