OK guys here we go. Bear with me on this one. THis is from start to finish on this build 79 f100 2wd C4
Engine for this build started as
1980 cast block, crank, heads and rods.

Mains and rods std
Pistons .040 over Cast Alum Dish.
Cam Speed pro # CS1020R 2000-4500 RPM 290/300 adv. duration .472/496 lift 112 lobe center
INtake Performer Air Gap
Carb 650 Holley Double PUmper *temporary* full race no choke on carb
Ignition duraspark, 8mm wires

NOTE: Carb Normally a 600 CFM Non Double pumper w/ choke but getting rebuilt and tuned at time of this post.

I have a slight hesitation / vibration at 1200 rpm and then it will scream.. is this from my cam or something fishy on the carb? or because of stock rebuilt tranny

Timing is set at 8 BDC
Any help is apprecaited

 

That sounds about right for a carbed motor with that much cam. A carb with vacuum secondaries will perform much better.

 

Ok I have the rebuilt 600 with vac second. on it.
It sputters at about 3400 rpm.. whats up?
I can deal with the low end flutter but when I want to get up and go .. Not a good thing?

Any suggestions?
Thanks
C

 

Get a wideband O2 sensor so you can see if the motor is rich or lean at that rpm and then make the appropriate adjustments to the carb.

 

could it be the old fuel pump not keeping up?
I have a holley blue in the garage with regulator

 

If it pulls fine above the sputter than no I doubt the fuel pump has anything to do with it.

 

No it doesnt pull fine above the stutter.. passing someone in a hurry on a two lane road is a chore for anything above 55.. now if its just highway cruising 70mph its ok.. but if i drop it down and try to run it up past 3k then sputter it goes.
I broke out the ol faithful Holley Blue pump and fuel pressure regulator and will slap it in tomorrow.. cross yer fingers.
Thanks
C

 

ok found the problem.. .. I dont know what its called but it is the little pot that hangs off the passanger side of the carb. There was a small tear in the diaphram. All is good now..

Thanks
C