Engine Stumbling? - Team Camaro Tech
Tech 2001 General Tech questions from 2001
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post #1 of 4 (permalink) Old Aug 29th, 01, 12:32 AM Thread Starter
Join Date: Sep 1998
Posts: 15

Hoave been trying to tune newly built 350 engine and started to have a problem. The timing is set at 12initial with about 12-13 of vacuum advance.
The problem is I set the idle at about 900rpm. It runs good for a few seconds and then starts to stutter and the rpm drop to 400-600. I can bring it back up by giving it more gas, then runs at 900rpm before stuttering back down to 600RPM. Thought it might be a fuel problem so I changed carb, then fuel pump with no improvement. Also new inline fuel filter. I have a fuel guage that reads about 5psi. When the engine stutters, sometimes the guage drops to around 3psi (but sometimes reads 5psi while stuttering). Could this be an electrical problem or a clogged in tank fuel screen? I don't think the tank is rusty inside. I can't figure out why the engine all of a sudden starts to run poorly without me doing anything.
BTW, it's a 350 with performer RPM components, an HEI and 600cfm Holley.
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post #2 of 4 (permalink) Old Aug 29th, 01, 03:02 AM
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Location: Houston, TX USA
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If you have recently had the intake manifold, heads, carb or other related top end pieces off-you should be looking for a vacuum leak. Your problem sounds exactly like a vacuum leak. Hook up a vacuum gauge and see what kind of vacuum you are pulling at idle and watch to see what happens when the engine starts to stutter and die. There are a few different ways to find vacuum leaks on a running engine. Try doing a search for those different methods.

1969 Camaro SS 350-383ci./365HP, T-56, 12 bolt, Power Trax Locker, 3.73 gears, 4 whl disc, Deluxe black houndstooth interior, rear window defogger, tilt steering, floor console w/gauge package, center mntd. clock, tachometer

[This message has been edited by Go69 (edited 08-29-2001).]
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post #3 of 4 (permalink) Old Aug 29th, 01, 09:08 AM Thread Starter
Join Date: Sep 1998
Posts: 15

I'll check that out. Thanks for the reply. If I can't find anything, I might just drop the gas tank to convince myself that things are OK.
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post #4 of 4 (permalink) Old Aug 29th, 01, 02:54 PM
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Location: Washington, Michigan USA
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Also sounds like it can't idle through the idle passages, and is idling through the transfer slot only; when the throttle plate settles back to normal idle position, flow tapers off to almost nothing thru the transfer slot, and no flow is evident from the idle passages. Idle passages blocked or idle air bleeds blocked? Do the idle mixture screws have any effect on idle quality or vacuum readings?

'69 Z28 Fathom Green
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