blu73

It is a 1973 with a slightly warmed over 350. It has an automatic trans with a stock convertor. The plugs are new. The gas is fresh. The carb has been recently rebuilt. The timing was set to factory specs, but has been tinkered with lately in an effort to get the engine running better. The vacuum advance is hooked up to the intake manifold directly. All other vacuum hoses are in place and connected. It starts well.

The problems are poor idle and drive-ability. It stumbles every few seconds like it is cutting out in some way, then recovers. When light throttle is applied to get going, it is very noticeable. It continues while being driven at constant speeds. When heavier throttle is applied to accelerate harder, the cutting out is there along with spitting back through the carb. The idle needs to be set high while in park in order to get the proper idle when the trans is moved into drive. The drive line gets quite a shock and the engine almost stalls.

Anyone out there that has had similar problems? Thanks in advance.

toobroketoretire

It sounds like the timing is way off and needs to be set again with the vacuum advance disconnected......................

DUB

Here I go a again. i have encountered many old engines where the harmonic balancer outer ring has spun and moved in the position of the notch in it. And this notch needs to be to CORRECTLY positioned to use a timing light if that is how you are setting your timing.

Also..I have come across many engines that have had a new timing chain cover installed and the timing tab was the WRONG ONE for the balancer being used. And this makes a BIG DIFFERENCE. Your timing tab should be almost touching the balancer.

Have you verified that the vacuum advance is actually working inside the distributor???
Are your advance weights able to move and retract back???
Have you check the dwell....just be be on the safe side??
Are you sure that your plug wires are GOOD??? And that they are NOT all 'zip-tied' together????

DUB

Zoix

I don't think you want vacuum advance on full intake vacuum.

LS4 PILOT

I had a bad ignition switch that would make my corvette stumble driving.....intermittent and aggravating .

I couldn't figure out what the heck was causing it ......it could be a thousand things .

So.....I brightened up.

Took it to a PROFESSIONAL auto mechanic . Not my uncle , third cousin, friends friend ....but to a guy who does such trouble shooting FOR a living five days a week.

Wow ...I know it's a novel idea .....LOL...

But it worked , hour labor and price of ignition switch.

Sunstroked

Points been replaced recently? Plug wires grounding out? After installing a msd 6a in my old camaro I had those symptoms. It wasn't until I opened the hood in the dark and saw the electric show going on in the engine compt that I figured it out.

blu73

Haven't been able to spend much time on this problem with yard work, dance recitals, work, etc.

Some good ideas here that I hadn't thought of. I'll be checking them out and hopefully get this solved. So far, I have only found the idle mixture screws needed to be turned in slightly for be best reading I could get on a vacuum gauge. This is about right for me. Nice driving weather and the 'vette is running like crap.

530planeman

How far are you from Cinn. I have been working on these cars for over 50 years and if you are not to far I could come give you a hand /
Wes

blu73

If you were to draw a line to the farthest point across the state from Cincinnati, you would be in the neighborhood. I'm between Youngstown and Warren. Thanks for the offer.

530planeman

That's nothing I just drove round trip to Florida and back to pick up an engine for my 70, 31 hours