TrimDrip

usually the floats are suppose to be set at 1/2 way to 5/8 full. Some people set the back ones full on double pumpers for extra fuel but 5/8 should suffice for this.

is your timing high enough? Too low of timing can cause a backfire through the carb as well.

I would get the float set or cleaned and raise the timing and see what happens.

Explosive

Hmm. Going on year two since it's been done so let me think back.

Once we got it running we ran it on a backroad and got the timing set. I forgot where exactly. We did have an issue last year with fuel. Wasn't getting any, obviously wouldn't run like that. you'd go to accelerate and it would fall on it face. Thought it was a fuel pump, replaced it. Ended up being a fitting on the steel braided line. It tore on the inside and the fuel caused it to fold and block the flow. I don't think any of that got into anything though.

TrimDrip

dude I think I told you wrong. I believe too much advance can cause it to backfire through the carb and too low can cause it through the exhaust.

so maybe the advance timing is causing spark before the intake valve closes?

TrimDrip

or maybe the float is too high causing the overflow and the jetting is too low causing the backfire. It is cold there so, that would cause one to lean out with such a cold air.

as you can tell I stick by my previous statement that I suck at these. Just trying to help though.

Explosive

I appreciate the help. As I can change settings ect. but suck at the diagnosis.

67mustang302

Set your timing first. Modified engines need more base timing, and a SBF with 10* that has heads/cam etc will most likely not want to idle properly. Get the base timing and timing curve right first. Then check the plugs to get an idea of jetting. You'll need to jet it up or down as needed. Then pick the right size power valve(which I seriously doubt is blown, no one has blown PV's since the 60's). Some say pick a PV that's have the idle vacuum, I prefer to go with one that's about 2-4" below idle vacuum...you can play with that later to see which one provides better part throttle. Then after all that change squirters and pump cams to get the pump shot correct.

Unfortunately for you the car doesn't have much adjustability beyond that, no air bleeds and no ifr's etc. See where you can get with the above first.

Explosive

Thinking about dyno tune now. See if they can get it.