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.