Help with QF HR-750

[JamesRR]

Get initial set, THEN, worry about total.

The bushing shouldn't matter getting the idle set properly.

Thanks. Its MSD billet.

 

[pjc360]

try some .029 idle feed restrictors

 

[ken5124]

I sprayed and checked for vacuum leaks. No rpm change when sprayed. I believe this is my cam.

http://www.summitracing.com/parts/cca-20-672-4?seid=srese1&gclid=COrRo-X8q70CFafm7AodIEEAog

My problem is I have low idle because if I turn in the idle speed screw too much it is exposing too much of the transfer slot and thus not running off of the idle circuit. Vacuum is very good in all other ranges. Is a .508 small in a small block street car?

best,
James

Are you able to use the secondary side to increase your idle speed? I have a quickfuel HR 600 and added the Holley Adjuster on the secondary side, which allows adjusting the secondary without taking the carb off. I can set transition slot on the primaries, then adjust idle speed with the secondary adjustment.

 

[UOP]

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.