mustangmanic69

I Have a 67 mustang coupe that I have been restoring for the past 2 years. I recently swapped in a motor that I pulled out of an 81 truck. It is a 302 unlike the original 289. I went ahead and beefed up the cam using my dialing wheel and dressed up the motor. to top it off I installed an edelbrock performer intake and a holley 650 carb. When I jump on the car and the secondaries open it sounds like its leaning out in top end and it pops. I have checked the timing and the fuel mixture and I still can't find the issue. Anyone have any ideas?

67mustang302

Well, first that 650 is prolly way too big for that engine, which is basically stock. Second, does it stumble or bog when you open it up, or just seem like it has a flat spot at high rpm? And does it pop through the intake manifold and only when you first open the throttle? Also did you change the cam, or change the cam timing?

mustangmanic69

when you open it up after you take off. take off on the primarys it runs fine and when you go straight to the secondaries it makes a loud pop and tries to die. the cam timing has been changed slightly but it has been adjusted with a timing light.

67mustang302

You're not gonna adjust your cam timing with a light, your ignition timing, yes, your cam timing, no. Is it a mechanical or vacuum secondary carb

mustangmanic69

vaccum secondary. I dont wanna deal with a mechanical. car pulls incredible vacuum so im just unsure on why its leaning out.

67mustang302

What's your vacuum at idle, what power valve and secondary spring does the carb have, what's the squirter size and what pump cam?

Colorado_Mustang

You'll have to adjust how the vacuum secondary is coming on. There is a spring kit you can by to try and dial it in. Have fun. That's the reason I run mechanicals...

67mustang302

Yeah, but you gotta tune the accelerator pump for the secondaries with a mechanical. 6 and one half dozen or the other as they say

Colorado_Mustang

Accel. pump is infinitely adjustable. There are 5 springs for the vacuum secondaries. Especially at higher altitudes, you won't find the right secondary spring that'll work.

67mustang302

My 570cfm runs the black spring(stiffest) from sea leve-4,000ft without problem. But it's also a setup using a small carb+good air pump for an engine, so it has good venturi signal. It helps on mileage too, espeically the way I drive