Help with QF HR-750

I have one of the HR series carbs and went through the same thing. You need to install smaller idle feed restrictors. The adjustment screws are still turned in about 1/2 turn out but the smaller idle feed restrictors really helped.

As others have mentioned, more timing helps idle. 18-20 seems to be the norm.

For setting the idle, take the carb off and square the transfer slots on the primaries only. You want to set idle with the secondaries with a double pumper carb. On the HR carbs the allen screw to set the secondary idle is pointed down, so in order to make it adjustable without having to remove the carb just pull the screw and put it in from the top. When you look at it you'll see what I mean. The only downside to doing it this way is you have to turn off the motor to set idle, but it keeps the transfer slots where they need to be.

I'd also go with a 3.5" power valve. I've found that the 1/2 vacuum deal from Holley isn't quite right and that a power valve that's 2/3-3/4 vacuum seems to run a little smoother.