speaking of lars, q-jet or holley?

[clutchdust]

maybe lars will step in and impart some wisdom
in the meantime, whoever wants to step up, i'm all ears.
i got a 750vs holley when i bought a bunch of stuff for my build a while back. problem is, my combo really needs something closer to a 650. just recently i picked up a q-jet from an '80 Z-28. i'm debating on whether to try detuning the 750 even further to work with my motor or just slap that q-jet on. right now i have 67 primary jets with a .028 squirter in the holley. even so, i have this super bad flat spot on tip-in. it gets better when the car warms up, but it's still there.
i always had good luck with my old q-jet so i'm thinking of just droppping the rochester on until i can afford EFI.

 

[lars]

Just a few facts, comments and opinions from me...

First, keep in mind that the Q-Jet is 750 cfm. Further, your 750 VS Holley is an on-demand carb with the vacuum secondaries, so it is not too big for your application, unless you're putting it on a 2.3 liter Ford Pinto.

Next, not sure what you mean by "de-tuning" the Holley for the application. You want to "up-tune" any carb for any application and certainly not "de-tune" it. A carb that is slightly too big for an application tends to run lean - not rich. So you don't want to decrease jetting. If anything, you want to bump the jetting up a tad. If a carb is too small, it will run a little rich, and may need to be leaned out. But that's not your case. Your flat spot is caused by a lean condition. You need to richen that carb up.

I have test run several hundred carbs on my car during my tuning and setups over the years, so I have run Q-Jets and Holleys back-to-back. Properly set up, a Q-Jet and a 750 Holley will run identical - I cannot tell a difference at all between the two carbs once they are both properly tuned. But to get the VS Holley to run right, you have to change the secondary spring - the stock spring is too stiff to allow the secondaries to fully open. Run the short yellow or the white spring if you want the full performance potential from the Holley.

Drop me an e-mail request for my Holley and BG carb setup papers if you want a detailed rundown on setting the carb up. Properly tuned, either of the two carbs will run just fine on your engine. If your car is too fast for you, drop down to a 650 to slow it down a tad...

Lars