There is no substitute for data logging. Why guys try to video their way to A/F data is beyond me.

If you cruise on the mains, when you lean the cruise that means smaller main jets which means you will need to open up the PVCRs to get the WOT mix back where it needs to be. And if the power valve is too late now, it will be a bigger issue with smaller main jets. I am not suggesting that that is the wrong approach. I am just noting the additional steps that need to accompany that route.

At what RPM is the timing all in? And with that big a cam, more initial may be called for if the starter will take it.

Whats with the first frame? Are you really idling at 1300 rpm with 9 inches of vacuum?

First thing that stuck out to me was, IMO, there is no reason for the engine with that camshaft to idle at 1200+ in P/N.

That engine should easily idle at 950 and a pull down to 850-900 in gear if the converter is OK. Might be a ground up issue to some extent, too much plate opening at idle.

I’m going to revive this thread instead of creating a new one. Now that I have a bunch of time on my hands I thought I would go through the carb and make sure everything is clean and the way it should be.

In the video above it looks like the engine is idling at 1200 rpm. Sometimes the needle will stick and not drop below that number. If I tap on the gauge it will usually drop to where it should be. I didn’t really notice it when I made the video. I was more focused on the vacuum reading.

I took some pictures of the disassembled carb. Maybe you guys can help me figure out if something is not quite right. I might look at buying some replacement metering blocks and was wondering if my base plate would support 4 corner idle.

I have the throttle blades set so that the transfer slot looks “square”. Is this where I should have them?

Here you can see what looks like some flashing partially blocking the channel. Is it supposed to be like this?

My Proform carb is identical to the 650 body on the primary side but the secondary side is different.

Here you can see how far the primaries open before the secondaries. Is this about right?

Are you using 650DP metering blocks and baseplate with a Proform 750 main body?

My experience is that the 650 metering blocks don’t play very well with that body.

The primary block from a 4777 has emulsion tubes taking up a lot of space in the main well.
And as I recall the angle channel on the secondary block is really more of a “horizontal” channel way at the top.
I don’t know if they were all like that.

4777’s never had 4 corner idle so a couple of extra holes need to be added to the stock base plate.

I’ve had a proform bodied carb built from a 4777 on the dyno before...... it didn’t run well at all.
On that carb, a pair of metering blocks fixed it.

QFT makes a kit with a pair of blocks if you haven’t gotten replacements yet.

Edit- looks like your secondary block has a normal angle channel.

If your primary block has the inner two brass plugs up on the top of the block looking “flat” instead of a “cup”, those are the tops of the emulsion tubes.
If all 4 plugs are “cups”, then it doesn’t have the tubes.

I built a number of those HP750’s from scratch when those main bodies were a pretty new thing.
I would use stock 4779 metering blocks and the stock 4 corner idle baseplate.
Those carbs always ran pretty well.

I won't and don't open the throttle plates enough to expose the transition slots, you want the motor to idle on the idle circuits only, not the transition circuits, correct The myth about the transition slots needing to be exposed at idle has been posted on here way to many times
I think if you open the throttle plates enough to expose the transition slots I also think that affects the power valve opening at low manifold vacuum

How much t-slot is exposed on the secondary blades.....I have found in SOME cases that the square ft. and rear t-slot exposure can help across the board and I set em all square to start then set the mixture screws accordingly. I also like the pink cams on the #1 setting......

On Dommy's, never any t-slot exposed but on 4150's always or it goes lean till the mains/boosters kick in but that's just my way and doesn't mean it's for everyone or every combo...

Thanks for the replies. All of the brass plugs are cupped.
I think I’ll look for for a nice 750 to use. I don’t want to mess with drilling out the baseplate and getting new metering blocks.

Do yourself a favor and step up to the technology that's available today w/billet blocks and bases which are lighter and better in every way.......Maybe even a alum. main body or better yet but a new carb w/all the features anyone will ever need or possible use.......No clue why folks keep messin w/the old junk unless you're broke of course then I get it.....

If you’re going to buy a whole 750 to use with that Proform body, make sure it’s a new enough one that already has 4 corner idle.
The older 4779’s didn’t have it.
I don’t know what dash number it was when the 4 corner idle was std.

I can’t quite make out what your stock main body number is.
4777-7?

That’s what I used to make my dyno carb out of.
I’m not sure what vintage the metering blocks are, but I believe they’re earlier than a -7 though.
They have the emulsion tubes in the primary block....... but if you’re working with a matched set of components from a 4777-7, then it would appear they had done away with that by that the time the -7 was made.

I used an aftermarket base plate, and modded the rear metering block and main body to have 4 corner idle.

I built this carb out of a new Holley 134-300S main body and a bunch of other QFT parts.

Nowadays you can buy a Street Q or Brawler carb for less that it cost to put this together.

I built a HP950 from scratch about 20 years ago using a genuine Holley HP bare main body.
When you bought one of those, bare meant “bare”.

For the end user, the only reason to try stuff like this is because you want to play with it.
There are some pretty good deals out there for carbs these days.

I see you worked over the venturi's to get rid of the flashing.......

That’s one nice thing about the boosters not being there.

I’m sure that’s a non-issue with a nice billet body.

The early Proform bodies would often have a pretty noticeable step there.
And usually....... only on one side.

Agree, and yes the billets don't suffer from casting flaws but not everyone needs one although on a flow bench they are dead consistent from venturi to venturi and have no casting issues. As you mentioned the Brawlers and a few others can be tuned in nicely and perform very well after a few mods.....

Thanks for the info and pictures. I've got a lead on a nice Holley 850HP Street. Looks like I could put my 750 main body on it and have it better sized for my combo. Eventually I would like to get a Holley Sniper. I currently don't have any type spacer under the carb. I do have room for a 1" inch spacer. What would you guys suggest for something on top of my Performer RPM?