VincentLuong24

Hi guys,
First post here! I have a '67 vert with a 427 3X2 that recent had its engine and carbs rebuilt. After the rebuild the car ran AMAZING! Smooth idle and revs all the way up the tach. After putting about 1000 mils on it or so we decided to change the break-in oil. While we still had the car on the lift, we also pulled the cluster to fix its bounce speed needle issue. After we thought we got everything fixed, we fired it up. It ran terribly. It didn't want to idle at all until it warmed up a little. It sounded like it was missing a bit from the passenger side pipe though. Any ideas what it could be? We tried changing the points to the Pertronix system with no avail. We went back to a stock replacement to no avail (although I'm not too sure if we got it adjusted correctly). Please let me know if you guys might have any ideas what it might be. Thanks!

5thvet

Have you checked the spark plugs and wires on that side that seems to be missing?

Don

VincentLuong24

Yeah I just pulled them. They LOOK good but I am just going to change them just in case. The spark plugs I mean.

VincentLuong24

So we just changed the plugs, rotor and cap to no avail. We tried messing with the gap of the points a bit but it didn't really seem to help much? Does it mean anything if you step on the throttle too quickly the car will backfire? I hope that's the correct term. Any advice will be greatly appreciated. Thanks!

Tiros

How does the timing look?

Frankie the Fink

Check the distributor hold down clamp for tightness. If that starts moving around on you, you'll get all kinds of oddball symptoms...

VincentLuong24

I'll check timing in a little bit and report back. The distributor cap looks to be on tight! Thanks for the replies!

KC John

I went through a time where my car was acting like yours and it turned out to be a broken exhaust valve spring. Tried about a dozen things before I finally pulled a valve cover and saw the problem.

Frankie the Fink

Not the distributor cap - check the bolt that holds the clamp at the BOTTOM of the distributor where it seats in the intake

JRRHINO

Broken rocker arm will also do this.

Tampa Jerry

Put a vacuum guage on the intake manifold. Sounds like you knocked off a vacuum line. If not, the vacuum reading will give you a quick look at the valves without pulling anything off. Jerry

Boyan

Did it backfire out the carb or exhaust?...
Boyan

Gary's '66

64365coupe

I would check the valve lash. If theres a loose rocker Id check to see why. Compression test too. Cant hurt and its easy. Thermal gun on exhaust manifolds can give you an idea which cylinder is giving you trouble a lot of times. Steve

bcwaller

I've had a loose rocker and a bent valve cause this, but your timing makes me think that the problem is external to the engine. Loose distributor, wire, vacuum hose, etc. since you were not doing much. Above tests will tell you a lot, as well as basic tests of pulling one spark plug wire at a time to see if that makes any difference before compression testing.

As this is an old Corvette, check the electrical system for floating grounds or a new short somewhere...

steve meltzer

Here's a question for the experts. Wouldn't a bad power valve do this? steve

Larry P

I just went through this and was looking at all suggested.
Completely overlooked fuel pressure, filter, etc.
Larry

SonnyAK

Recently i adjusted the carb on my L72, during a very cool/dry day...Soon after the weather turned super hot/humid and my car started running much like yours...Have you been tweaking your carbs any lately?

mashinter

Make sure your plug wires are installed correctly.
Follow the firing order from the cap to the plugs.

Frankie the Fink

I still haven't seen where he's checked the dizzy hold down clamp...