JohnNC

1970 350 2 barrel, basically stock, but has had the tranny swapped for a TH400. I removed the Thermo Vacuum Switch and TCS solenoid. I am running one manifold vaccum to the distributor vacuum advance, and another manifold vacuum to the transmission modulator.

Car starts and runs fine. Once warmed up, I can put it in gear and it pulls away no problem. As soon as I give it gas, it stumbles big time. If I punch it, no problems. It's just that at part throttle it almost dies.

When in neutral or park, no problem at all. Revs very smoothly.

I've had this problem since I got the car. I replaced the carburetor, no change. Then removed the TVS and TCS. Runs better, but still have the problem. I have checked dwell and timing, adjust the fuel air mixture, still have the problem.

Any ideas? Could the transmission swap be the issue? Maybe something overlooked that caused a vacuum issue? Should I change the distributor vacuum advance?

Thanks for any ideas. Driving me crazy!

Rickman48

What happens when you pull the vacuum advance hose + plug the hole while running??
Have you looked at the centrifigal weights? Are they free?

MDchanic

Like Rickman says, check your centrifugal and vacuum advance to be sure they're working.

Also, are you sure that the carb you replaced yours with is good?
While it could easily be the vacuum advance unit, it's also got the sound of a bad accelerator pump (or leaky pump BB).

- Eric

Destructor

Or possibly a clogged intermediate circuit in the carburetor.

oldcutlass

Accelerator pump, And as mentioned above, Distributor mechanical or vacuum advance issues!

Run to Rund

Check the accelerator pump squirt (air cleaner removed; engine running or not running). If no squirt, either the pump is bad (the seal is leaking) or the check ball at the bottom of the well is corroded in place and not letting the fuel through.

MDchanic

OR the opposite - the check ball isn't sealing well against the float bowl, allowing the fuel in the tube just before the nozzles to leak back into the pump, causing a delay in spray when you step on the gas - either one is possible.

- Eric

JohnNC

Thanks for the feed back, I really appreciate it!

The pump does squirt when I manipulate the throttle, but not immediately. I will pick up a rebuild kit and swap out the check ball and see if that does it. If not, I'll move on to the vacuum advance. Hopefully get to it by the weekend. Thanks guys!

MDchanic

It should be immediate, as soon as you begin to move the throttle.

The way to check is to give it a good pump, then give try it again immediately afterward.
If it comes out immediately the second time, then it's slowly leaking back through the check valve. If it's no better the second time, then it's a different problem.

If the ball is leaking, you need to use the old ball to re-form the seat before putting in the new ball - just set the old ball on the seat and give it a few good taps (but not too good) with a hammer and punch to shape the seat.

- Eric

JohnNC

I think you are right about the accelerator pump. It takes a good two or three pumps, which are kind of weak, before I get a nice immediate squirt of fuel. I will pick up a rebuild kit, reform the seat, and try it out hopefully this weekend. Thanks again for all your help!

MDchanic

You're welcome!

... But let's see if any of our advice helps .

- Eric

JohnNC

Resurrected this thread from the dead. I've been on the world tour (Texas, Kyrgyztan, Afghanistan, Kuwait, germany, Texas, New Mexico, Louisiana and back home). So in the last few months, I did an HEI swap, internally regulated alternator, and attacked the carb.

I whacked the old check ball with a hammer a few times and put in a new check ball. Then I replaced the rubber seal and spring on the accelerator pump. The problem is 90% solved. I think I need to adjust the timing and the fuel air mixture. I also am looking at an electric choke conversion because it seems like my choke is totally inoperative.

I also started cutting a custom plug wire set. 5 down, three to go. It looks awesome!

I'll keep you guys posted, but in a more timely fashion!

oldcutlass

Cool welcome back!

Gone Johnson

What ended up happening?