Holley 750 dp setup

Greg Stump · 03-13-2009, 07:57 PM

Just wondering about setup of a 750 Holley HP Double pumper.This is on a 355cid/tubro350 3000 stall ,4.56 geared,3600lb ,street strip car.I,ve been working on getting idle correct.It has correct power valve for the idle vacum it has.I had to start by jacking the secondiers open to keep the primiary blades in correct realtion to the transfer slot.This seemed to be the right fix because it cleaned up the stumble it had when cracking the throttle open but, it seems there is a lot more rpm drop when car is shifted into gear.1300RPM to 700 in gear.Is there any way to keep primary in correct postion with the transfer slot with out having so much RPM drop? Also should 4 corner idle screws be adjusted in gear or out of gear? Thanks in advance.

69ss/rs · 03-13-2009, 10:52 PM

First, start with the four idle screws one and a half turns out. Do this without the car running. Don't turn the idle mixture screws more than two turns out. Back the main idle screw up until the blades are close.Now give the main idle screw two full turns open. Start the car and see how it idles, let it get up to operating temp before you make any adjustments. This should be a good starting point. If you still have the big Rpm drop when you put the car in gear, gradually open up the secondary blades a 1/2 screw turn at a time till you get the idle you want. If this doesn't work than the convertor may not loose enough for the size cam that you have. Hope this helps.

Terry Cain · 03-13-2009, 11:06 PM

You might try drill front butterflys with about a 1/16" bit and work you way up until it feels good.

Myron Piatek · 03-14-2009, 06:46 AM

I've found them to idle better and drop less rpm in-gear when you open the idle mixture screws 1/4 to 1/2 of a turn more than what's optimum in neutral.

BlueOval Ralph · 03-14-2009, 08:59 AM

When you set the idle seed with the prim and sec screws (not the ones in meetring blocks) never expose the transfer slot more that .060 thou. If you can not get the idle speed you want, thats when you drill holes on throttle blades if you have four corner idel do it in both prim and sec also. Start at .060. Also it will do you well to open the idle feed resct in meetering block .003 thou. (most 750 are .031 or .033 from Holley.
Ralph

Quote:

Originally Posted by 69ss/rs

First, start with the four idle screws one and a half turns out. Do this without the car running. Don't turn the idle mixture screws more than two turns out. Back the main idle screw up until the blades are close.Now give the main idle screw two full turns open. Start the car and see how it idles, let it get up to operating temp before you make any adjustments. This should be a good starting point. If you still have the big Rpm drop when you put the car in gear, gradually open up the secondary blades a 1/2 screw turn at a time till you get the idle you want. If this doesn't work than the convertor may not loose enough for the size cam that you have. Hope this helps.

Ron Miller · 03-14-2009, 11:45 AM

As Blueoval Ralph suggested, I would open up the idle air bleeds .003 to .006 before I drilled the Primary throttle blades. I would rather mix the added air in the idle channel sooner than in the added holes in the throttle blades. Getting the idle mixture correct, you might see a increase in vacuum. Also use a good vacuum gage to adjust all your idle mixture screws. Adjust in park and check in gear. Adjust screws in or out to achieve the highest manifold vacuum. When idle is adjusted correctly their will be a increase in manifold vacuum. You will have to change the power valve. To choose the correct power valve, put into gear, foot break the engine to launch r.p.m. and look at vacuum gage. Example,,,,, if the vacuum reading is 9 to 8", choose a power valve 1.5 under that reading.

Ron

BlueOval Ralph · 03-14-2009, 12:13 PM

As Blueoval Ralph suggested, I would open up the idle air bleeds .003 to .006 before I drilled the Primary throttle blades.

Note: I DID NOT SAY TO DRILL THE IDLE AIR BLEEDS, BUT OPEN THE IDLE FUEL RESTRICTION GET A LARGER AMOUNT OF FUEL IN THE SYSTEM. Holes in the the throttle blades will not hurt you, infact it has been used in some production carbs.

Quote:

Originally Posted by Ron Miller

As Blueoval Ralph suggested, I would open up the idle air bleeds .003 to .006 before I drilled the Primary throttle blades. I would rather mix the added air in the idle channel sooner than in the added holes in the throttle blades. Getting the idle mixture correct, you might see a increase in vacuum. Also use a good vacuum gage to adjust all your idle mixture screws. Adjust in park and check in gear. Adjust screws in or out to achieve the highest manifold vacuum. When idle is adjusted correctly their will be a increase in manifold vacuum. You will have to change the power valve. To choose the correct power valve, put into gear, foot break the engine to launch r.p.m. and look at vacuum gage. Example,,,,, if the vacuum reading is 9 to 8", choose a power valve 1.5 under that reading.

Ron

03-13-2009, 07:57 PM	#1
Greg Stump Junior Member Join Date: Mar 2006 Location: Mechanicsburg PA Posts: 13 Likes: 0 Liked 0 Times in 0 Posts	Holley 750 dp setup Just wondering about setup of a 750 Holley HP Double pumper.This is on a 355cid/tubro350 3000 stall ,4.56 geared,3600lb ,street strip car.I,ve been working on getting idle correct.It has correct power valve for the idle vacum it has.I had to start by jacking the secondiers open to keep the primiary blades in correct realtion to the transfer slot.This seemed to be the right fix because it cleaned up the stumble it had when cracking the throttle open but, it seems there is a lot more rpm drop when car is shifted into gear.1300RPM to 700 in gear.Is there any way to keep primary in correct postion with the transfer slot with out having so much RPM drop? Also should 4 corner idle screws be adjusted in gear or out of gear? Thanks in advance.

03-13-2009, 10:52 PM	#2
69ss/rs Junior Member Join Date: Feb 2009 Posts: 82 Likes: 0 Liked 0 Times in 0 Posts	Re: Holley 750 dp setup First, start with the four idle screws one and a half turns out. Do this without the car running. Don't turn the idle mixture screws more than two turns out. Back the main idle screw up until the blades are close.Now give the main idle screw two full turns open. Start the car and see how it idles, let it get up to operating temp before you make any adjustments. This should be a good starting point. If you still have the big Rpm drop when you put the car in gear, gradually open up the secondary blades a 1/2 screw turn at a time till you get the idle you want. If this doesn't work than the convertor may not loose enough for the size cam that you have. Hope this helps.

03-13-2009, 11:06 PM	#3
Terry Cain Senior Member Join Date: Feb 2008 Location: Georgetown, Indiana (close to Louisville, KY) Posts: 773 Likes: 530 Liked 228 Times in 105 Posts	Re: Holley 750 dp setup You might try drill front butterflys with about a 1/16" bit and work you way up until it feels good. __________________ Terry Cain ???? STK tcain19689585@gmail.com

03-14-2009, 06:46 AM	#4
Myron Piatek VIP Member Join Date: Nov 2001 Location: Florida Posts: 1,542 Likes: 34 Liked 138 Times in 51 Posts	Re: Holley 750 dp setup I've found them to idle better and drop less rpm in-gear when you open the idle mixture screws 1/4 to 1/2 of a turn more than what's optimum in neutral. __________________ LOCOMOTION Racing

03-14-2009, 11:45 AM	#6
Ron Miller Member Join Date: Mar 2002 Location: Brownstown, Mi 48134 Posts: 196 Likes: 35 Liked 13 Times in 7 Posts	Re: Holley 750 dp setup As Blueoval Ralph suggested, I would open up the idle air bleeds .003 to .006 before I drilled the Primary throttle blades. I would rather mix the added air in the idle channel sooner than in the added holes in the throttle blades. Getting the idle mixture correct, you might see a increase in vacuum. Also use a good vacuum gage to adjust all your idle mixture screws. Adjust in park and check in gear. Adjust screws in or out to achieve the highest manifold vacuum. When idle is adjusted correctly their will be a increase in manifold vacuum. You will have to change the power valve. To choose the correct power valve, put into gear, foot break the engine to launch r.p.m. and look at vacuum gage. Example,,,,, if the vacuum reading is 9 to 8", choose a power valve 1.5 under that reading. Ron