72 Skylark stalling

jrlaia7

Member
I’ve been working on my skylark. rebuilt the carb, fixed vacuum leaks, and car was running great.


went out last night, and the car started dying under load. on the highway it was stumbling, and by the end of the drive, it was cutting out completely and dying. Whether at low speeds and slow acceleration or fast acceleration.

I haven’t done a pressure test on the pump - but I did a flow test a week ago and the pump was pumping strong.


but like I said, car was running great all last week. I don’t think it was vaporlock, as it was not hot out, and I’ve been driving the car all last week in much hotter temps, and the car was fine.

suggestions?
 
How about spark distribution, a problem in the cap and rotor, or grounding or cross firing plugs. You didn't happen to tie your ignition wires together to make them look tidy?
 

jrlaia7

Member
How about spark distribution, a problem in the cap and rotor, or grounding or cross firing plugs. You didn't happen to tie your ignition wires together to make them look tidy?
Thanks for the reply.

the cap, rotor, are new. put in an hei tune up kit.

the previous owner zip tied the wires together on each side
 

jrlaia7

Member
Any chance the smog pump or diverter valve could be contributing to the problem?

diverter stuck open?
something to do with it getting hot?
 
Not sure I can comment on the smog pump diverter valve, but definitely cut the zip ties. Plug wires MUST be separated. If the ties are the problem you will notice a difference immediately.

Plug wires should be kept 1/2" apart when running parrellel to each other. They should not have any contact with metal surfaces. IF, like when leaving the distributor, they must cross over each other, they should be as close to a 90 degree angle as possible.
 

LARRY70GS

Active Member
Sounds like fuel to me. You need to recheck your pump, or simply buy a new one, they are cheap enough. If the pump is old, the ethanol in our gasoline may have done it in. I hope you used a good rebuild kit on your carburetor. The Parts store ones may not be the good ethanol resistant ones. The accelerator pump will be the first to go from the ethanol.


 

jrlaia7

Member
Sounds like fuel to me. You need to recheck your pump, or simply buy a new one, they are cheap enough. If the pump is old, the ethanol in our gasoline may have done it in. I hope you used a good rebuild kit on your carburetor. The Parts store ones may not be the good ethanol resistant ones. The accelerator pump will be the first to go from the ethanol.



Thanks for the info.

funny enough, the old accelerator pump worked fine. Still rebuilt the carb. New one works fine.


After spending some more time under the hood, I don’t think the problem is engine related. I’m guessing it’s the torque converter.

Everything under the hood is working and tuned up as it should. I wanted to swap out the th350 for a Muncie, so it’s a good opportunity to do so.
 

twood

Member
What Transmission do you have? I had a stalling problem at acceleration and found that my vacuum modulator on my TH400 was shot....Easy and cheap to replace....
 

LARRY70GS

Active Member
Torque converter problems generally involve stall speed, or stator problems.

Stall speed problems are usually the result of engine modifications involving a different camshaft. Lots of guys think installing a high performance cam in an engine is a free lunch, you get more HP with no downsides. That is not the case. You can actually make a car slower and a lot less fun to drive with a bad camshaft choice. High Performance cams hold the valves open longer so the engine can breathe at higher RPM, where they can make more HP. But, the downside is a rougher idle with less vacuum available, and a loss of low RPM torque to gain more HP at higher RPM. That's where you need more stall speed and numerically higher rear gears, to get the engine into the higher power range faster.

Torque converter stator problems are another thing altogether. They are relatively rare, Either the vehicle has poor acceleration or top speed is abnormally low.

 
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LARRY70GS

Active Member
What Transmission do you have? I had a stalling problem at acceleration and found that my vacuum modulator on my TH400 was shot....Easy and cheap to replace....
The stalling was probably the result of a huge vacuum leak because of the modulator diaphragm being damaged.
 

jrlaia7

Member
The stalling was probably the result of a huge vacuum leak because of the modulator diaphragm being damaged.
Actually, did a 4 speed swap on it this past week. Same issue. Seems to happen when it gets up to temp. Ran fine driving up and down the street, and to the grocery store. Then just started dying while moving at speed. Had a hard time starting it back up. When it did start, couldn't get it moving.
 
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