348 Stalling Issue

[Kevin Shelly]

Hey All. I’ve been trying to remedy an issue I’m having with my stock 348, 250 HP, Powerglide Impala. The car runs great. Timing and all are good but as the motor heats up and I need to change gears from Drive to Reverse or Park to Drive or Reverse, the motor stalls out. If I come to a stop sign or traffic light, it stays running. The only time it stalls out is when I change gears. It’s driving me crazy. Any help would be great. Thanks in advance.

 

[blkblk63ss]

Years ago working in a dealership had a mustang would stall like that. The tranny guy found the torque converter to be defective . It would stall in reverse. Maybe might not be your problem ,but I thought I would throw it out to you.

 

[oldskydog]

Vacuum modulator leaking?

 

[Kevin Shelly]

Thank you for the message on the torque converter. I can check that out.

The vacuum modulator is tight. I took it off the trans and tested it as best I can and it didn't leak. The trans shifts good from 1st to second and back again. The engine idles nice and when it's not all the way up to temperature, it works great, even going between the gears. It stalls out only when it's at operating temp and I try to go from drive to reverse or park to drive or reverse. I live in the Denver area so I'm at about 5000 feet of elevation. I've been also trying different main jet sizes to get it to run a little better from a start and hopefully not stall when hot. I went down a few jet sizes and that didn't help so I went back to where it was. I believe I have .058's in for the main jets and .062" for the secondary. It had .064" in when I got it but reading a bunch of articles about how to adjust a carb for altitude, it stated to start about 2 sizes smaller. The motor feels sluggish to me from 0-50 MPH. Over 50 MPH, it seems OK. I hit the gas and you can feel the torque and it goes faster. Below 50 it's just sluggish and doesn't really pull. Not sure if this issue is related to the stalling but I'm searching. I had the carburetor rebuilt by a guy down in FLA and it looks great but something is just off I believe?

Thanks guys.

 

[Don Jacks]

Increase your idle speed 100 rpm and ricen the idle mixture about 1/4-1/2 turn and see what that does.Remember that today you have lower octane fuel and alcohol to deal with.A few extra degrees of timing won't hurt either.

 

[Kevin Shelly]

Thank Don. I'll give that a try. When I got the carb back, I adjusted the mixture screws to achieve the max vacuum for each screw. I increased the idle all the way upwards to about 500 RPM's more than the book says and it still stalled out but of course that was way too fast an idle. I was just trying anything at that point. I'll increase the idle mixture as you said and see what happens. Thanks again Don.

Kevin

 

[blkblk63ss]

Check your tranny fluid ,see if it smells burned. You say it is sluggish in lower speed, to me I am thinking that is a torque converter.

 

[Kevin Shelly]

The trans fluid doesn't smell bad. I've smelled worse but the color is off a little. It's slightly purplish brown. I've had the car for 3 years now and don't know when any service has been done on the trans? Maybe it's time for a fluid change as well as some new fluid?

 

[blkblk63ss]

Yes change fluid and add a conditioner with it . I would change again in a few miles since there is no drain on torque converter . That way you will be flushing complete system of old fluid.

 

[Kevin Shelly]

Sounds like a good plan. I'll give that a try and see what happens. Thanks to all for your help. I'll keep you posted.

 

[blkblk63ss]

Don' forget to change filter.

 

[Kevin Shelly]

I won't. I'm looking it up now. Thank you

 

[blkblk63ss]

Working in a dealership we had issues with tranny shudder when shifting in overdrive. Even though fluid did not look that bad ,we serviced them with a conditioner and solved the problem. Sound's like your trans service was needed any way. Hopefully that may cure the problem ,if not I would still not rule out tc.

 

[Don Jacks]

Check your manuals.That old cast iron Glide might have a converter drain on it somewhere.

 

[Kevin Shelly]

Hi Don. The powerglide in my car is from 1964. It’s an aluminum unit that must have been replaced when the original turboglide went south.

 

[La Hot Rods]

Is the throttle pressure linkage hooked up?

 

[Kevin Shelly]

Not sure I know what that is? There is linkage that connects to the transmission from the carb.

 

[La Hot Rods]

That would be it.
Does the car slam into gear or just idle down and die?

 

[Kevin Shelly]

For the most part I get a small surge then it just shuts off.

 

[Fathead Racing]

If the engine is getting a little tired with the heat at running temp could be losing some vacuum at near idle rpm. When you have the vacuum advance pot hooked to manifold vacuum sometimes the vacuum unit starts to leak and your distributor mechanical advance drops to low without the added vacuum advance that "needs" to be hooked to manifold vacuum by the way! You need to check that the vacuum advance unit is in fact hooked to manifold vacuum. Next you need to check the vacuum advance unit and see if it will hold vacuum. You will need a vacuum pump to do this. Under normal setting the stock timing at idle with the functioning vacuum advance unit will be as high as 21 degrees advance. Check that vacuum advance unit. Your timing may be retarding.