This has been an on-going problem, that I just can't seem to fix. When you start the truck, it idles great. But, when you go to step on the gas, it boggs down, and trys to die. If you then feather the peddle, you can keep it running, and can accelerate up to 55 MPH, but the second you hit the slightest of a hill, it will do it again. Here is the engine configuration.

400 bored .030
.508 intake & exhaust lift / 278 duration cam
flat top pistons
heads shaved .10
deck shaved .10
4 bbl Edlebrock street master intake
Holley 80508S 750CFM Carb
Stock ignition

Here is what I have done to try and resolve the issue...

New 6.5 Power valve in the carb - no help
New 4.5 Power valve in the carb - no help
New #66 jets in the carb - no help
re-timed the engine with a timing light - no help
Complete tune up with new cap, rotor, wires, & plugs (auto lites)

Now, if I take the 750 off of it, and go back to the stock 2bbl carb, it runs fine, so the problem is in the carb. How do I fix it? Every mechanic that I have talked to, says that a modified 400 (like I have mine modified) should have no problems drinking down a 750.

HELP!!!!

 

I'm not sure about this but just trying to help ,how about the vacume advance at the distributer maybe with all you've added it needs an ajustment?

 

Are you using the same fuel filter on both carbs.?

 

I am doing something very stupid, and currently running NO fuel filter...

 

At least that rules it out as being the problem.

Is the choke working right on the 750? What about a vacuum leak?