I'm preparing to buy a Quick Fuel adjustable sec diaphragm, to be used with my 750 Holley (VS of course) which is also retrofit with the Proform main body. I did a search, and read nothing but good things about the Quick Fuel diaphragm. But I'm wondering... If I got the Quick Fuel diaphragm, should I also expect to be doing some spring changes? And if so, would the Holley quick change spring kit be compatible with the Quick Fuel part? Any ideas? Thanks

I have the Quick Fuel housing that you are referring to. There is a "new" version and an "old" version. The old version based on what I saw from pics posted on these boards put the screw to adjust secondary vacuum in the lower housing. If you got one of these, then you could use the Holley quick change setup (I assume you mean that black two piece top part). BUT the "new" design (which I have) moves the screw to the top piece of the housing and so it is one or the other. Can't use both. But you shouldn't really NEED to do both. Changing springs changes the rate of secondary opening, when it starts and can potentially limit total opening if a stiff spring is used (from what I have read). The Quick Fuel housing comes with the lightest spring installed so you know it will open all the way. And so by using the screw on it you can vary how fast the secondaries come in. I think you will not need to change springs. If you do, it won't be very often. I am sure someone more knowledgeable can chime in but that is what I have learned.

HTH

Good reply

What you're saying about the Quick Fuel housing not needing spring changes must be true, because I don't see any of the Quick Fuel users mentioning spring changes.
And since the two parts won't fit together anyhow, I'll pass on the Holley part, and just buy the housing.

Thanks