My dad has a friend's 1985 El Camino in his shop with an LG4 setup on top of a GMPP 330 HP crate engine. The car will idle at 750 RPMs awesome, and will light the tires when you step on it. But if you drive it normally, it will cough and sputter and choke. If you rev it up at idle, you can hear the exhaust sputter and miss all the way up the powerband. I'm no carb expert and this has stumped my dad, and he has other projects that need his attention. Has anyone else came across this? Thanks.

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That sounds like one of the primary main jets or possibly one of the transfer passages has some trash in it. The idle circuit bypasses those, as does the secondaries; but at cruise and part throttle, it sounds like it's leaning out bad.

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"So many Mustangs, so little time..."
ICON Motorsports

 

Thats definitely what its doing, leaning out at part throttle.

 

I just put a "new" carb on and its idling the best it ever has, and WOT is very good, except im having a similair problem. Off-idle up to about 2300 rpms its fine, but then it will stutter and drop rpms for half a second, and then go fine the rest of the powerband. If i punch it off the line its fine all the way too.

I've concluded its a lean problem, but could it just be that the MCS/IAB is not adjusted correctly? I haven't adjusted it yet, or the TPS for that matter.

Alright i need to adjust those first before i ask questions.

 

It turned out to be a piece of the hood insulation stuck in the carb. Hahaha! Thanks guys.

 

Don't they make air cleaners to prevent that?

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82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R. 2.93 limited slip. Cat-back from '91 GTA, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LB9 w/ZZ3 cam, TBD heads, exhaust, paint, etc.).
57 Bel Air, my 1st car. 0.030 over 396, Weiand Action+, Edelbrock 1901 Q-Jet, Jacobs Omnipack, 1-3/4" headers, TH400 w/TCI Sat Night Special conv & shift kit, 3.08 10-bolt, AMSOIL syn lubes bumper-to-bumper. Best 15.1 @ 5800' Bandimere. Daily driver while Camaro was being put together.

 

Yah, but the guy had driven it without the air cleaner. Doh!

 

These humans... what a species.

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"So many Mustangs, so little time..."
ICON Motorsports