[mustangman65_79]

Maybe i should explain a little more about the vac sec spring.

When someone, like u have a comibation, like a bigger cam, highrise intake, open air filter, full lenth headers, etc u lose vac psi at the carb. The vac sec spring rely on this to open up the sec. So to counther this affect, u need to go out and buy these springs which are lighter.

When u buy the kit, there should be about 7 springs in it. 6 of which are listed, the other 1 is not. I'd start with the one that is not listed, and u can tell that it is the lightest spring in the pack. Pu tit in, and go run the piss out of it. If your motor bugs out at say, 2,000 or so RPM, the spring is too light, and then u move on to the bext, trying it too. If it doesn't bog out, then it should be ok.