Hello,
My Mustang won't start so I'm rebuilding my Holley carb, which I believe leaks gas probably from the power valve into the manifold. I'm going to make a couple changes and I need some feedback. Below are my Mustang's specs as best as I can describe them. The Holley is an aftermarket add-on model number 0-6919, type 4160, vac. sec., elect. choke. It originally came with #62 primary jets, #39 metering block, black vacuum diaphragm spring, 2 stage power valve which opened at 12.5" and 5.5", 0.031" pump nozzle, and an orange pump cam in #2 position.

When I first rebuilt it years ago, I changed the spring to purple, the pump nozzle to 0.035", and the power valve to a 9.5". It ran fine, except for a slight hesitation when I floored it (probably due to too light a spring).

I want to change the spring to the next grade heavier, plain medium; change the pump nozzle back to 0.031"; change the pump cam to white #218 #2 position; and use the 6.5" power valve included in my rebuild kit. I read in"Holley Carburetors" by Dave Emanuel that carbs which come with 2 stage PV's typically have lean jets. My question is, will installing a 6.5" PV cause my engine to run too lean? Does the 6.5" PV change I want to make sound too lean when used with a #62 jet for the Mustang below? Despite what the book says, after reading some posts, it seems about right.

1968 Mustang
302 stock engine, pistons, cam
Edelbrock Performer Dual Plane manifold
Headers
Mallory Unilite Distributor with vacuum advance
Stock differential
C4 Auto

 

With stock cam I would use the 6.5" valve in the kit. #62 jets sounds lean for an older engine. I use #70's jets and had #72's at one time. The #31 Squirt is enough for stock engines.

 

I thought powervalve choice depended on the vacuum your engine produces at idle. Subtract 5 from that reading to get the correct PV...or some rule of thumb like that. You probably do not need the 2 stage PV.