For a street driver, at least - no ported vacuum. If you want vacuum advance, you have to go manifold.

Thanks to Craig84Z for pointing that out to me. I'm sure I had heard that before, but spaced it out when I got the part. I just hooked the vacuum line up to the metering block nipple and went on my merry way, never checking for vacuum or vacuum advance function. I did notice that it seemed to need pretty rich primaries to get decent cruise, which wasn't its primary use, anyway. Now with the advance hooked up to the manifold source it's really rich in cruise (even though it's relatively cold out today).

Of course, another (major) disadvantage to it for a driver is lack of a choke. Took a few minutes to get it to idle on its own after I first started it this morning.

 

I guess you'll need to do some tuning before you can give me some new results

later,
Craig

 

What jetting are you using with the new main body?

What main body and jetting did you replace?

if you look at your old main body and the new one you may be able to see whre the vacuum passage for ported vacuum is.
May just need to be drilled through. The gasket that goes between the main body and throttle plate may be blocking the vacuum passeage too.

If not,,, you can look at the lower throttle plate and see where the passage for ported vacuum runs.

You could drill a hole from the edge of the body to the pasage and press in a small tube to allow you to hook up a vacuum line.
Some old OEM carbs were made like this with the ported vaccuum down on the throttle base plate.

 

Okay, where to start...

I had 70 jets in the primary, they recommended 74's (high altitude, you know). I had a 650 Holley that was "transformed" with the Proform. I jetted down to 68 after the above post, and guess what, the cruise surging got worse!

I think this is what was going on: Without the vacuum advance, the power valve was kicking in during cruise. This lead to dark plugs. At the track, the plugs would "gray out" under WOT, indicating fairly close jetting. So, I assumed the dark plugs were due to rich cruise jetting and jetted down, where it probably was just the PV being employed because of lower vacuum without the vacuum advance. 71's or 72's will be close, I think (haven't tried it since the weekend). It was still fine at WOT with the 68's, by the way - 80's in the secondaries (Proform recommended 84's).

Now, about the ported vacuum passage. When I rejetted, I could definately see that there was a port in the body where the metering block mates, and the gasket was not blocking it. I'll have to trace it out with the Holley some day when I have a chance to take the carb apart again. IF I decide to do that, since it actually seems to run quite nicely now with the manifold vacuum on the advance (better than my Holley experience, anyway).

 

Hummm may need to adjust the airbleed cause you're at high altitude. Just a thought.

How much manifold vacuum do you have at idle and at typical cruise speed .....@ altitude?

Do you think the idle circuit (idle feed restriction+ idle airbleed) is rich or is it the main circuit (main jet + high speed air bleed)@ cruise?

Do you have a O2 sensor that you can use as a tuning tool?

I'm kind of interested cause I have a 700cfm DP that I want to upgrade with the proform main body and billet baseplate.

Bought it real cheap with a cracked baseplate.

 

I don't have an O2 gage. On the wish list.

It's the main circuit at higher cruise speeds that was rich. Now it's lean, because the PV is staying closed (I presume). Lower cruise speeds, such as surface streets, was fine. Idle is great now with manifold vacuum advance. I haven't fooled with the airbleeds, but altitude may be affecting that, too.

I need to put the vacuum gage on again. I've been tuning by ear, to simply getting it to run acceptably at the track. Since I tend to keep it cooler at the track than it does driving on the street, street idle has been a little high. But, again that was w/o vacuum advance. Now it purrs partially or fully warmed up the short time I've had it functioning again.

Oh, idle vacuum was only about 11" last I checked. Altitude plays a big part there. I haven't checked cruise vacuum, because I picked the PV to eliminate off-idle stumble.

 

Do the proform main bodies come with butterflys?

I'm wondering because the one listed for the 650/750 DP is the same part number.

I have a 670cfm street avenger and was wondering if I could use the 750 VS proform main body.

 

The main body is just that - the main body.

You re-use your throttle body, metering blocks, float bowls.

You need to check the numbers on the throttle blades and ensure they match what Proform says their body goes with. I've never heard if the SA's are covered by the Proform.

 

You think the Proform main body could support the off-idle (ported) vacuum passage with a carefully drilled hole or two to carry the vacuum from the throttle body area (where the port actually is) to the proper passage in the primary metering block?

 

I would think so, but I didn't look carefully enough at it to know whether they left out any material in that area.

Turns out mine works just fine with full manifold vacuum.