[Bobs78TA]

I have a 463 with 310cfm SD ported E-Heads, 10 to 1 comp., UD 234/242 112CL HR cam, Performer RPM intake, TH350 with Cont. Jim Hand torque converter, 3.42 to 1 rear axle, PS,PB,and AC. Would like any information or help on tuning for a new Holley 4781-8 carb.

[Tom Vaught]

4781-8 Carb will be a "4 corner idle" carb Set each idle screw 3/4 - 7/8 turns out from seated. Don't monkey around with trying to set each one individually, make them all the same.

HR Roller Camshaft with 234 duration @ .050 should idle easily at 10-12" of idle vacuum. Leave the front Power Valve alone. Block the rear Power Valve and go up 6-8 jet sizes on the rear jetting. Add jet extensions and a notched flow if mostly a track vehicle. Leave front jetting at 80s initially until you go to the track. When at the track try and find the best 60 ft times (clean launch) with the primaries. Tune the secondary jetting for best MPH.

Cliff Ruggles has a carb similar to yours (except 2 corner idle). He needed a 50cc pump on the front and a 30 cc on the rear to get the carb to launch well with the tight "Hand" type converter. Swap the pump, the pump cam, and the pump arm as a assembly. Readjust the set-up for .015 extra movement of the pump rocker arm with the throttle/pump arm at wot on both the primary pump and the secondary pump. The pump squirter on the primary might need to be .035" or larger to get the car to leave properly. Stock is #31 (.031")

Make sure the notched float clears the jet extensions (I use Holley jet extensions).

Don't use a "pancake" type cheap air cleaner. Get a good dropped base air cleaner from someone like Larry N.

If you are uncomfortable with any of the mods, send the carb to Jeff, Shaker455 and he will make the same mods that I recommended to you here. He and I are friends and I have no issues with sending him the work (if required). He was a Very Slow Learner but I think I got him worked into shape finally!! (:>))))))))

Tom Vaught

[Skip Fix]

Sounds similar other than gears(4.10 29.5 tall tires) to my pump gas motor, flat tappet hydraulic 239/247@ 0.050 112LS close.The first issue I had tuning was setting idle mixture up with the car in neutral. The Hand convertor was tight enough to load the motor and it was actually lean when in gear at idle.Caused a big off idle hesitation until I did that.Wouldn't mind if it was a "hair" looser at idle.

I ended up 2 jets leaner front. Plugged rear PV and 6 up from stock in the rear with notched float and jet extensions. In cool air it ran great, this year in the heat it had a bad bog at the line so I swapped the 50cc pump on the front-I had been running 30cc on both to compare with the Demon 850 I was running.And added the 35 squirter up front-just no track time since doing it and now cool air!

My wide band AFR helped diagnose alot what it was doing. The Holley has a better fuel curve cruising and part throttle acceleration than the Demon did, otherwise they performed identical on the dyno.

[Tom Vaught]

If you did need to go slightly larger on the idle feed restrictions to richen the idle, that is a very simple 5 minute operation. You might try opening up the idle mixture first to 1 turn out on all 4 screws first before you did any drilling on the carb.

Tom Vaught

[johnsma22]

Originally Posted by Tom Vaught

...send the carb to Jeff, Shaker455 and he will make the same mods that I recommended to you here. He was a Very Slow Learner but I think I got him worked into shape finally!! (:>))))))))

Tom Vaught