HELP with 350 stalling issue

[JFC10]

I have a 69 C10 longbed with the 350

I recently put a cam in it, specs are:
.420/442 lift
204/214 duration @ 50°

I also converted it to HEI and slapped a Edelbrock 1405 on it, with a spacer to convert it to work with the stock intake manifold.

Other than that the truck is stock.

I have a weird issue with the truck dying when you give it more than 3/4 throttle. Mash it from a stopp, dies, mash it while coasting, dies. I have my timing set at 4° advanced. Bumping it around does nothing to remedy the stalling.
At idle in park/nuetral, you can rev it up and there's some hesitation, but it doesn't die. I'm thinking the hesitation might've been a hint, so I messed with the accelerator pump adjustnent and that does nothing either.
What causes a aftermarket engine to stall like this?
What should the timing be for a slightly better than stock cam?
I'm out of ideas, I'm sure someone tuning wizard could hear it running and fix it in one step.

[harpo231]

I'm thinking your timing should be around 12-14....

[Steeveedee]

Do you have the CD that came with the carburetor? Follow their recommendations. I'm willing to bet that you are going to have to jet it a little richer. I put a 305 SBC in a '68 Skylark (because I had it) and it fell on its face until I jetted it a little richer, and not by all that much, as I had a 700-4(R) behind it, and was using it for a commuter car. I could get 17.5 MPG in stop and go traffic out of it.

[davepl]

If you "roll" into full throttle rather than "stabbing" it, does that work? I'm wondering if it's just an accelerator pump issue and it's bogging due to air stall.

Set the timing more to more like 10 degrees BTDC, I'd think.

[RedRider]

May be a silly question, but you have a square bore to spread bore spacer/adapter right?

[tdangle]

Don't worry about the timing right now. Even though a bump in initial timing can help performance, it won't fix what you are having happen. I suspect that you are basically flooding the engine when you mash it full throttle. I'm thinking the secondaries are opening very quickly and the engine just can't handle it. Can you disable the secondaries from opening and then try it?

Also something to check: Is there any chance that when you floor it the choke is closing. I see that it is a manual choke and if you dont have it wired open or connected with a cable that the air flow could be pulling the choke plate closed, choking your engine.

[demian5]

Originally Posted by harpo231

I'm thinking your timing should be around 12-14....

On a good running engine, you should be able to time it to 0 and it shouldn't stall.

[Jrainman]

Originally Posted by tdangle

Don't worry about the timing right now. Even though a bump in initial timing can help performance, it won't fix what you are having happen. I suspect that you are basically flooding the engine when you mash it full throttle. I'm thinking the secondaries are opening very quickly and the engine just can't handle it. Can you disable the secondaries from opening and then try it?

Also something to check: Is there any chance that when you floor it the choke is closing. I see that it is a manual choke and if you dont have it wired open or connected with a cable that the air flow could be pulling the choke plate closed, choking your engine.

I agree with Tdangle ,but also could be fuel starvation , if tou have a original 5/16 fuel line it may be to small requiring a 3/8 fuel line also fuel filter or fuel sock may be dirty ,

as you say when you stab (mash stomp ) on the gas pedal when it dies do you mean stall out the engine completly or does it catch its breath, and rpms start to climb back up. if it stall completly you are getting to much fuel , if stalls (boggs) down but comes back to life (rpms increase ) fuel starvation is happening.

[68 P.O.S.]

First off, as a general rule, you always make sure your timing is in order before you start adjusting your carb. This includes setting up your mechanical and vacuum advances on your HEI as well. Factory timing specs for a 350 is 8 degrees btdc. Cam manufacturers suggest adding 2 or more degrees when installing larger cams (you’ll have to look at the paperwork for your cam). At the bare minimum your timing should be at the factory 8 degrees. 10-14 degrees as harpo and davepl suggested will be just fine; I’m a 14 degree kinda guy myself. Get the timing right, then test drive it to see how the symptoms are. When you get to the carb, it sounds to me like the step-up springs may need to be changed. How much vacuum are you pulling at idle?