Stumble on takeoff?

[Sons 1st truck]

Just purchased a 71 c10 with a 283 v8 that has been sitting for 15 years. I put in a new fuel tank, fuel lines, fuel pump, and had the stock GM 2 jet rebuilt. I also put in HEI, new plugs, and wires trying to solve this problem. The truck starts right up and runs great, but from a dead stop if you try to give it too much gas for a fast take off it either dies completely or almost dies but comes back to life with tons of power for a 283. The timing is set at 8btc. Any suggestions?

[OrrieG]

Accelerator pump usually, but you said you had it rebuilt so that should be ok. Make sure it is working, maybe the cup did not seal or port did not get cleaned. Might bump the timing just a bit to 10 or 12 and see if that helps. Did the advance seem to be working when you timed it?

[Sons 1st truck]

Thanks OrrieG. I don't get on the computer much, but it Turns out the acc. pump was bad. Still stumbling though. I'll check the timing tomorrow. However I do have an unrelated question maybe you might be able to also help me with. I want to add power brakes and was wondering if i just need to buy the new booster and master cyl. or do i need to change out the distribution/proportioning valve too? Thanks

[nvrdone]

how long has the truck sat with gas in the carb? I find if mine sits more than a month or so with out running the ethanol fuel separates causing gum in the jets and fuel bowl. I have to take it apart, clean it all out & then it runs fine.
What I finally did id put a shut off valve between the carb & fuel line. Turn off the fuel, run the carb dry and no more problems.

[OrrieG]

I believe that the proportioning valve does not care if it is boosted or regular pressure. If the existing manual mc has two lines to a proportioning valve that serve a drum/drum or disc/drum setup then you should be good. If you are changing from single without a proportioning valve, or from disc/drum to disc/disc just get a prop valve that matches the mc. All the prop valve does is make sure one end stays working when the other end fails but the internals are specific to the type of brake system.