1986 C20 stalls sometimes

[Zach86]

I have a 1986 crew cab short bed with the following modifications. It’s a 350 I put summit vortex heads on it with scorpion 1.5 roller rockers, retrofitted comp cams roller lifters, a crane roller cam .488 intake & .509 exhaust, edelbrock 2116 intake, edelbrock 1406 carb, a huggers GM5Xtm torque converter on a th400, with a 4:10 rear end. MSD coil, MSD box, MSD wires. My truck starts up and runs fine but if I punch it from a dead stop it won’t spin the tire, posi is my next add on. Once it’s rolling around 40mph it will run strong when I floor it. But it’s a dog below that. I was doing donuts in the snow the other day and it would just stall. Any suggestions?

 

[SirRobyn0]

Well I'm not sure I'll be of much help, but I'll throw some stuff out, maybe someone that is more of an engine builder than I am will come along and confirm or deny my suspicion.

What about that camshaft? When is it suppose to make power? And what about that converter? If your to far below the power band when you punch it from a dead stop then ya no tire fry for you.

As for the stall doing donuts, how hard were you running it? Edelbrocks are notorious for being sensitive to the float set. They are also notorious for coming out of the box, new with the float set to high. Take it apart and check the float level.

Hopefully something there is at least somewhat helpful.

 

[75gmck25]

On the Edelbrock, check your transition slot exposure when the throttle plates return to normal idle. It should be approximately square at normal idle, and then set the idle mixture screws to get best idle mixture.

If the idle mixture is off but someone then set the curb idle up higher or lower to compensate, the transition slot exposure may not be correct. It may still idle fine, but as you initially accelerate the mixture will be wrong during the transition from idle to cruise throttle.

Also take a look at the Edelbrock step-up springs. They are easy to swap. These springs are rated in inches of vacuum, from about 4”-8”, and they adjust the point where the carburetor rods transition from cruise to power mode. For example, if you swap to 8” springs it will go to power mode (richer) as you accelerate and vacuum drops to 8”, but with a 4” spring it will wait until vacuum is down to 4”. Stock is probably a 5”, and I would try at least a 7” spring.

Also, what is your base timing? 12 degrees BTDC would be my absolute minimum, and I would try bumping it up to 16 degrees. Then check to see that you get about 20 degrees more from mechanical, preferably by about 2000 rpm if you want low end power.

idle