New 350 Chevy runns rough and won't idle

66nova · #1 (**permalink**) 07-31-2002, 07:22 AM

Here's what I have rebuilt 350 .40 over GM Vortec heads with larger springs, 480 cam, airgap intake, GM HEI, 600 Holley. I have the motor set at top dead center and the distribitor set very close to the number one terminal (pointing to cylinder 1) Runs very rough and does not idle. However, the first time we had the motor running for 5 minute and though we were off little and re indexted the distribitor. Now it won't idle and back fires

Help any one

Mertz · #2 (**permalink**) 07-31-2002, 09:03 AM

Ok this may be a really dumb question but are you trying to run at TDC? It should be around 10 BTDC. If you don't have a timing light you can set it statically. Make sure you are at TDC on the Compression stroke. Feel it air is coming out of the spark plug hole. Rotate the engine so the timing mark reads 10. Now if the distributor rotates clockwise which I think it does, rotate the distributor clockwise until it stops. Pull the #1 wire and set it close to a ground so you can see it arch. Turn the key on but don't turn over the engine. Rotate the distributor counterclockwise until you see a spark. Do this a couple of times to make sure you get it right. Tighten the dist. and your at 10 BTDC. If you have the rotation wrong you woould be on the other side of the cap contact and your timing would be way off. The idea is that the rotor touches the cap contact setting off a spark at 10 TBDC.

Remember to check that the #1 TDC is on the compression stroke and not the exhaust stroke. Sometimes it will run but not very well. I have had mine off on the corvair and it would run but very rough. When I bought it the guy had the wires off one cylinder. It would run there too if I moved the distributor enough but not well.

Hope this helps. My major problems with rough idle have been vacuum leaks and poor carb setups. Check for vacuum leaks by spraying brake cleaner around the base of the carb and other vacuum connections. My 350 is not running well because the carb is floading at idle.

396 · #3 (**permalink**) 08-01-2002, 10:48 AM

does it back fire from exhaust or thru the carb could be a valve too tight

bullheimer · #4 (**permalink**) 08-01-2002, 01:22 PM

18436572

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