My 72 dart has a horrible hesitation from a stop. Would me changing my power valve in my Holley 4779-7 carb help this? Im new to the Holley world and really want to learn how to replace one. I picked a 6.5 replacement one from auto zone. This might sound dumb, but is there one or two, and if so, what one do I change?

-Thanks-

 

Or would it be my accelerator pump? Is it too big. Like I said before, my car falls on its face until rpm's rise then the car takes off.....

 

Dart -

Could be all of the above + s few other things, including the "wrong" carb for the application. (Too big a carb.)

Holley Vac secondary carbs have a single PV in the primary metering block, double pumpers MAY have one in the secondary metering block. The secondary one is optional.

Measure your vacuum pressure in inches idling in gear and divide by 2, that's the size valve you need. Ex if your vac in gear was 13", then you need a 6.5, etc.

Newer Holley carbs have a backfire bypass circuit that help to prevent PV blow outs in case of back fires, older ones (pre 1992, IIRC) don't, but you can add one if you like.

The accelerator pump may be bad or you could have the wrong acc cam - hard to tell.

Make sure the carb circuits are clean and that you don't have a vacuum leak.

Archer

 

Here is some info I hope will help: http://www.holley.com/data/TechServi...ech%20Info.pdf

 

Is this on a stock motor ?? If the idle screw has the throttle blades open to far it could cause your problem

 

You really just want your power valve about 2" below idle vacuum. You don't want it opening at idle but you want it to go to work off idle. Dividing by two will cause an unwanted delay and make the hesitation even worse. Most of the time you just need to check your accel pump to make sure it is working the instant you get off of idle. That's usually the hesitation issue. If idle vacuum is 8 then go to a 6 or 6-1/2 to keep it closed at idle. I don't think this is your problem to begin with. It would flood at idle if it was opening or had a rupture in it.

 

What should my vac be at or around? And I will check my accel pump. If I open the throttle wide open the car will just about stall.....

 

Dart -

Vac pressure depends on the cam, valve size, compression, etc, etc. Only way to know is to measure it. I have a vac gauge on my secondary instrument cluster.

Archer

 

Im going to change my Accel Pump from #28 to a #31...accordingly to Holley's instructions.

 

I have seen MORE mis-adjusted accelerator pumps than anything else! I have seen them set where they come in way too late. And also cranked down so much, that there is no pump-shot left by time the accelerator starts to move.