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Old 05-23-2012, 10:29 AM
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350sbc 4bblwith Holley carb

Hey guys I think I need to fine tune this engine ....and I need help ...car starts no problem and runs good at idle ... But when I attempt rev it pops in carb and stutters to rev up or accept fuel ...what's going on here

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Old 05-23-2012, 12:11 PM
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*****Start with a engine compression test**********. The secondary side of the ignition system is the usual suspect. Inspect and replace cap, coil rotor, wires, plugs as required.
A Hot aftermarket coil need s steel center pin on a HEI. The stock resistant carbon center pin will overhat and burn the cap and rotor with anything but a stock GM coil. A common fault MSD makes the steel pins that go with their swap in HEI coil.

Carb may be flooding ( fuel filter, dirt in needle seats) this will foul the plugs.
replace the plugs and fix the carb. Blown power valve will do the same thing ( back fire thru carb blows the PV).

Fouled plugs will idle but will not take throttle load. ( misfire)
They rarely can be cleaned once carbon fouled. replace.
Idle fuel pressure not more than 7psi.
Look for and fix any all carb/ manifold vacuum leaks. Broken hoses etc

Make sure the engine is grounded to the firewall with a ground wire and good contact points.

Google search: vacuum gauge diagnostics, then go buy one and use it.

Last edited by F-BIRD'88; 05-23-2012 at 12:18 PM.
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Old 05-23-2012, 04:34 PM
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maybe

Had a afb years ago did the same was vacuum leak because the butterfly bushings in secondaries was worn and thus a vacuum leak unless its a new carb look there
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Old 05-23-2012, 04:56 PM
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Quote:
Originally Posted by Dirtdolla
Hey guys I think I need to fine tune this engine ....and I need help ...car starts no problem and runs good at idle ... But when I attempt rev it pops in carb and stutters to rev up or accept fuel ...what's going on here
Does the accelerator pump deliver a shot of fuel the instant the throttle is opened?
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Old 05-23-2012, 05:33 PM
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Not a new carb but intake was removed ....never took carb off intake just took apart as one ...cobalt ...yes to your question or to me it is from what I can see ...like maybe a lil too much I'm thinking I guess I should back down on idle throttle and play with air/fuel mix .....question I got is ...what piece of diagnostic equipment can I buy to properly diagnose
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Old 05-23-2012, 05:40 PM
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Quote:
Originally Posted by Dirtdolla
Not a new carb but intake was removed ....never took carb off intake just took apart as one ...cobalt ...yes to your question or to me it is from what I can see ...like maybe a lil too much I'm thinking I guess I should back down on idle throttle and play with air/fuel mix .....question I got is ...what piece of diagnostic equipment can I buy to properly diagnose
I suppose a wide band air/fuel meter might help diagnose and tune it, but the cost is high.

Before going that route, I would try more or less accelerator pump shot to see if that showed me anything. You will need to use different accelerator cams and possibly shooters to tune the accelerator pump circuit. More on that HERE.

If that didn't cure it, I would be sure the advance curve and the initial timing is enough for the engine- too little initial advance (retarded timing) will cause the engine to pop back through the carb.

What is the carb number? What do the plugs look like?
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