chucktn

Got a 73, 4spd, 350, with a new fuel pump, new gas tank, new fuel line "S" style, and return line that is specified in tech articles. Rochester was rebuilt about 6 months ago by a Corvette shop it has a HEI ignition. Here's the problem. When the car reaches temp on warm days it seems to starve for gas starting around 3000 RPM's. Thought it was the fuel pump so I changed it out I thought it was fixed now it's started again. Thought maybe it had was getting a vapor lock so I installed the factory recommended "S" hose. You can see fuel pumping into the carb when you work the throttle. Tank is new and clean. The other problem is that once it quits running and you shut it off and start it again it may run fine for a little while. I was wondering if my problem is electrical in the distributor since it does it when it's hot and 3000 RPM's or more. Looking for suggestions.

0Willcox Corvette

Chuck,

Here is a bump for you and some input.

When it quits and then starts back up, is there a delay?

Will it run and continue to drop off again at 3000 rpm’s?

You said it has HEI, is it a GM distributor or after market? (MSD, or other)

When is the last time you tuned up the car? Have you checked the coil to see if it’s working properly? Depending on the HEI you are running you may have a bad coil.

If it’s HEI from GM, the coil is located in the top of the distributor. If it’s an aftermarket HEI system then you have a coil in regular place.

If you are running HEI aftermarket ignition, did you get the coil to power it up. In other words, MSD distributor and a blaster coil.

If you are running HEI GM have you checked the module in the distributor?

You answer some of these questions and I’m sure someone else will pop in for you.

chucktn

Thanks for the quick reply.

It's a Mallory ignition.

It drops off at 3000 RPM's and then gets worse and eventually will quit running.

Will start back up, but hard.

Installed a new distributor cap, rotor and new wires less than 1K miles ago but did not change the ignition coil.

How is the best and most accurate way to test the coil?

0Willcox Corvette

Is it one of those breakerless ignition systems?

If you have a service manual on the car it will tell you how to test the coil. I have a test at my office and I guess I should put this up on the web site since I never remember it. I can post it tomorrow for you or someone here will tell you real quickly.

I had a Mallory breakerless system in one of my cars fail too! Food for thought.

Willcox

cargo247

what about an air lock at the tank ????? crack the cap a bit and see if that helps just a thought

0Willcox Corvette

I just thought of something.

If you run the breaker less point system in your car, you can not use the old power wire that ran to the points. It is a resistance wire and will drop voltage to the newer system when it heats up.

You need to find another source for switched voltage if you are wired this way.

It’s easy to tell; this wire has a yellowish tint to it and looks like it has a woven sheath over it.

If the voltage is not 12 volts to the breaker less system it will break down under load.

Willcox Inc.

chucktn

All good points but if the car hadn't run so strong until recently I would agree that there could be a wiring issue. The dist was in it when I bought it almost a year ago so this isn't a new addition. I've read other posts and I'm leaning towards the ignition coil, any thoughts on that being the culprit?

71406

You said your "tank is new and clean". But you didn't mention anything about the sock on the pickup tube in the tank. Ifs its bad it can create the type of symptoms you describe in your post.

r44s

Do you have a filter in the carb, they can be a problem.

chucktn

The filter is new in the carb and the sock looks clean but I just talked with a fella who said to take the spring out of the filter that sometimes creates a problem and to also take the outer sock off in the tank. He said that sometimes the outer sock looks good but the inner type filter/sock can be a problem.

I guess these are symptoms but my problem starts when the car is warm and typically is at around 3000RPM's and gets worse from there.