When jetting for best performance whats the rule of thumb for secondary jetting for every certain jet increase on the secondary side what should you do to the primary?

 

Have you converted the 4160 style secondary metering plate to a 4150 style metering block?

Typical jetting is 6-8 jet sizes bigger in the secondaries when you only have a primary power valve.

 

yes it has a 4150 style secondary block

 

right now i have 66 and 70 jets in there should i try to bump the secondary side to 72? stock l98 centerbolt heads and 207 213 .415 .430 lift (l98 cam). The mods are in the signature.

 

I'd say go ahead and bump the secondaries to 74 and see how it goes.

FWIW, the Proform main body uses a 12 jet size spread between the primaries and secondaries. 4 is certainly too little, 8 isn't likely to be too much.

How does it run on the primaries?

 

it runs pretty good at the track it used to bog on take off but awile back you recommended the adjustable housing and it works great. Had it set at the preset 2 1/2 turns and slowly backed it off till i felt bog then turned it back in half turn so 3 1/2 turns works great for me sounds like a bit much but i dont feel it opening and it leaves hard. on the street it drives just like a fi car except cold start have to let it warm up if i start it and try to drive it immediatley it will cut off. Doesnt blow black smoke like most older carb cars around here.

 

Sounds like the primaries are close then. Try 74's, see how it acts.