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Need help trouble shooting

I have a 85 corvette 427 small block chevy swapped. 4 barrel quickfuel electronic choke carb.

I was out driving when out of nowhere the car wouldn’t put power down, when on the gas it shakes front to back and is running pretty bad. Shifts fine, doesnt seem like rear end problem to me. Checked the plugs had a bit of carbon build up, was running pretty rich a few weeks ago but have since then adjusted the carb. Now it smells like it’s running lean. Only thing I’ve done to the car before it started acting up was tighten the very loose valve covers, problem started right after that. Anyone have suggestions? It’s much appreciated!

Have you been using gas that contains ethanol?


No, just regular 93 octane. Did run 91 once a few months back to see what it prefers.

Yes, that is fuel that contains ethanol. Gas from the gas stations has 10% ethanol.

What are you using for a fuel pump? An external or internal pump? What type? What type ignition system? MSD electronic trigger or something else?

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You should watch this.


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External fuel pump, Quickfuel HR 750 carb. Honestly dont remember the exact fuel pump on the car. MSD streetfire HEI disrupter, Taylor Spiro-Pro spark plug wire set.

I would suspect a fuel delivery problem. Temporarily install a mechanical fuel pressure gauge and go drive the car. If the pressure is ok, around 5 - 7 psi even at full throttle, focus next on the carb itself. Open it up and see if a gasket came apart or some crud got in.

I’d also look for evidence of an ignition problem or a wire that may be grounding out.

BTW. Does this Vette have the Dana 44 center section or the Dana 36. A big block in front of the 36 will soon have you looking for a 44!


Thank you for the help, I will try your solutions. Does have a Dana 44. Its a auto with a reverse manual valve body shift kit and the Dana 44 rear end from a manual c4 vette. motor is currently sitting at 550ish to the wheels. Looking to push more, just gotta learn what it’s like to have a carbureted motor first. I’ve had bikes with carbs but this is my first built car with a carb.

That’s a lot of weight in the front

What did you do, in regards to the suspension?

A 427 small block? swapped? 4 barrel quickfuel choke carb?

Good luck with your problem.

I suspect you live in an area with no kinds of smog inspections whatsoever

In my neck of the woods you’d never even get a bar referee sticker, because a 427 and a carb were never offered on any 1985 Corvette sold in the US

Personally, I would have put in a newer all aluminum Corvette motor, but everybody has different tastes

Which automatic transmission . . . big blocks and small blocks typically don’t use the same transmission

He has said he has a 427 small block, not a big block, no extra weight, just bigger bore and stroke. Chevy has used them in racing Corvettes for quite a while or you can build one with aftermarket parts.
Are you using a fuel filter? You should be to keep dirt out of the carb. Too little fuel pressure can cause this, but so can too much. Too much can lift the float and overflow the carb dumping liquid fuel into the manifold, flooding the engine.

Has z51 suspension

The car has Hooker Super Competition Headers 2151HK down to 3 inch pipe straight back. I live in indiana, emissions laws aren’t strict. I do have mufflers to put on just have yet to.

I am using a fuel filter, I’ll look into the fuel pressure thank you for the advice

This happened right after you tightened down the valve covers? Do you have high clearance valve covers? Some cam/rocker combos need the high clearance covers or the rockers can hit. Just a thought.

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Thanks @oldtimer. I guess I’m an exceedingly old timer who should keep up with Chevrolets better. It’s hard to imagine getting 427 cu in from a small block though. The 400’s had cylinders that you could see through

Yeah, I know, the first time I saw one , it was running at Lemans (on TV) I wondered how did they do that?

There was a 440 ci small block featured on PowerNationTV that they built for a Camero. It is an aftermarket casting that accepts LS heads. Made a lot of power.

Feel a bit stupid after finally finding the problem. When I tightened down the valve covers one of the bolts also holds a bracket for the spark plug wires. The wire got pinched and starting arcing off the valve cover. Had a hard time telling it was a misfire due to the cam, got a new wire and plug on there now. Thanks for everyone’s advice!

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