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Old 02-22-2013, 10:26 PM
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New Engine Need Help

Watched a whole lot of videos, read a whole lot of posts and rebuilt a SBC 350 by myself. Had a rough idle, found out I was using wrong spark plugs. Have Vortec heads. Changed spark plugs but have another problem. Car will start it will rev around 1200 RPMs for couple minutes and then RPMs drop and eventually die. If I rev it up, it will rev high again and later die. Need some help what could cause this and how to fix it. This is my first engine I built so maybe I missed something or installed something incorrectly. Oh yeah I have a Carter 600 carb and a Street Demon Carb and it does the same thing with both carbs, so I am ruling the carb out. Mahalo for your folks help.

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Old 02-22-2013, 10:35 PM
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may not be a carb problem, but sounds like a fuel problem or perhaps a vacuum leak
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Old 02-22-2013, 10:55 PM
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Originally Posted by prumora1 View Post
may not be a carb problem, but sounds like a fuel problem or perhaps a vacuum leak
I read to check for a vacuum leak to spray carb cleaner and if the idle changes there is your leak. Is there any other ways to check for a vacuum leak? How would I go about to check if it's a fuel problem? I don't have a fuel pressure gauge, maybe I should pick one up. Thank you "Premora1". Will do some checks tomorrow.
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Old 02-22-2013, 11:34 PM
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What else is on the engine? how extensive was the rebuild? Make/model/year?
More info would be helpful.

Check timing, vacuum etc...
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Old 02-23-2013, 12:16 AM
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What else is on the engine? how extensive was the rebuild? Make/model/year?
More info would be helpful.

Check timing, vacuum etc...
Just the basic aftermarket bolt ons: headers, intake, MSD ignition. Block was from a '79 Blazer 4X4. Had machine shop rebore the cylinders, new pistons, stock crank, vortec heads. Installed it in a '84 Monte Carlo SS. I tried to check the timing but the timing mark is bouncing all over the place. Cam is a mild cam so I know with the timing mark bouncing is not normal, but can't figure out why.
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Old 02-23-2013, 01:31 PM
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Don't use a dial back timing light with a MSD ignition. Most will perform eratically, trust me. Get hold of an older timing light without the dial back function. May be able to borrow one from autozone.
Need to get the timing close before starting to adjust carb. Make sure to disconnect vacuum advance hose from distributor and plug carb port.
You may need to adjust the valves while its idleing. Is the cam(flat tappet) broke in yet? If not do that first.
Engine may be getting too hot from retarded timing. Try about 10 degrees BTDC to be on the safe side just to get started. If you dampner isn't degreed, get a timing tape put on it to help set up your advance curve. Don't go over 34-38 degrees max total timing(not including vacuum advance). Test drive hot in high gear up hill at WOT(under load) to listen for detonation after your sure the carb float level is correct.
Thats just some things to get going. Need to adjust idle with a vacuum gauge(in gear with auto trans).
FWIW
ssmonty
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Old 02-23-2013, 02:37 PM
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Sounds like it is running out of fuel. Does it start right back up after it dies or do you have to wait. Could be a plugged fuel filter.
The other thing that comes to mind is something in the ignition system is heating up.

More info on the engine and symptoms will make it easier to troubleshoot
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Old 02-23-2013, 02:44 PM
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Check for intake leak or under base of carb. You can squirt some carb spray in the carb, this will richen mixture, that might tell you if you have vacuum leak. Make sure hoses are all on and in the right place too.
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Old 02-23-2013, 04:17 PM
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Originally Posted by T-bucket23 View Post
Sounds like it is running out of fuel. Does it start right back up after it dies or do you have to wait. Could be a plugged fuel filter.
The other thing that comes to mind is something in the ignition system is heating up.

More info on the engine and symptoms will make it easier to troubleshoot
I have to give it some gas and it'll start right back up. I am going to pick up a fuel pressure gauge to check what my fuel pressure is. I am running a mechanical fuel pump.
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