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holley accelerator pump tunning?

  • Thread starter Thread starter 68dustin
  • Start date Start date May 18, 2010

68dustin

Member
Oct 8, 2008
173
2
19
May 18, 2010
#1
  • May 18, 2010
  • #1
ok this is my setup
68 mustang 2900 lbs
302 bored 30 over
weiand accel intake
trick flow twisted wedge heads
decent cam cant remember duration
t-5
4:11 gears
paxton supercharger 8lbs boost
750 holley 4150 blow thru carb


this is my problem:

off idle with a jump no bog, however when im driving and crusing in lower rpm's and jump on the throttle it stumbles. When the rpms are higher it really doesnt bog. But i noticed wot thru first to second fine and then going into third it has a slight bog and the wideband goes lean. where should i start on my accel pump?

carb setup:

70 front jets
72 rear jets

37 front accel nozzle
35 rear nozzel

ive tryed switching the nozzles front front to back and it made it worse so im thinkin the front ones needs to be bigger. should i set it up to a 50cc pump? ive played with all the cam adjustments and it seems just to get worse. im running the pink cams in the first slot. the bogg is horrible but i want my carb running tits! lol.. thanks guys i know ur holley freaks up in here
 

robbz28

10 Year Member
Sep 23, 2009
775
5
39
Epps, LA
May 18, 2010
#2
  • May 18, 2010
  • #2
I would definately upgrade to the 50cc pump, because that 30cc just isnt feeding the volume you need. I would try upgrading only one at first. Also buy the hollow high volume screw for the pump squirter. If that don't fix your problems you will have to buy some new pump squirter cams....these are no fun to play with, but when you get a holley that is what you get into. All your other numbers sound good, but that darn stumble can be a pain to get rid of, good luck!
 

68dustin

Member
Oct 8, 2008
173
2
19
May 18, 2010
#3
  • May 18, 2010
  • #3
thanks, yeah so do i have to get the hollow screw? or is there a certain # squirter i reach then get the hollow screw?
 

robbz28

10 Year Member
Sep 23, 2009
775
5
39
Epps, LA
May 18, 2010
#4
  • May 18, 2010
  • #4
They kind of go hand in hand, i don't know why they don't package them together. You don't get the full benefit of the 50cc pump without that screw. Moroso and holley both make that screw.
 

65FBE2

Member
Mar 8, 2007
283
0
17
Minnasnowta
May 21, 2010
#5
  • May 21, 2010
  • #5
Doesn't sound to me like it has anything to do with the pumps. Idle to wot in low gear would give you the biggest bog if it were excel pump. Have you checked the timing curve? Rear jets seem small to me, Why would it go lean only in 3rd? Power valve maybe? I'm no Holley expert but been playing with them for 30+ years and most of the time it turns out to be timing. I have 0 back ground with a super charged motor though.
 
1

10secgoal

Active Member
Dec 1, 2003
2,801
3
49
San Diego
May 21, 2010
#6
  • May 21, 2010
  • #6
Totally contradictory here, but.. It's definitely pump shot. Shouldn't need the hollow screw until about 42 on the squirter. Never needed a 50cc. Really don't see a lil 302 needing one.You need more fuel, but your 37 may even be a bit large. The cam gives the squirt it's volume, and times the volume. if you look at some of them, they are larger up front than others offering more volume up front for the hit, then taper off.

Others start a little late, but provide that volume a little longer. Squirts you use to fine time the timing of the shot. The bigger, the more you get up front for the exact same pump shot cam. Squirter will offer no extra volume.
It does it in 3rd because that is the biggest load compared to the other gears. Also probably why it doesn't do it in first or off idle. The load is so light, it doesn't show lean.

The pump shot only cover lean spot until the fuel is pulled from the mains. make sure the floats are right. If they're too low, you never get enough pump shot

Have you changed the back cam also ?
Why that spread in the carb ? Did you block the PV ?
 
V

v8only

Active Member
Jul 3, 2003
2,378
22
49
May 22, 2010
#7
  • May 22, 2010
  • #7
how is it with those 70 primaries? I have the same intake, slightly smaller heads with gt40 aluminums...I upgraded to 68 primaries and it runs rich as hell while cruising now...66's work perfectly for me....I'd bet you have a ton of fumes and it's running rich while cruising??
 
1

10secgoal

Active Member
Dec 1, 2003
2,801
3
49
San Diego
May 22, 2010
#8
  • May 22, 2010
  • #8
If you idle speed is set correctly, your jetting should have very little effect on cruising.
 
V

v8only

Active Member
Jul 3, 2003
2,378
22
49
May 22, 2010
#9
  • May 22, 2010
  • #9
I agree with that, I was going off topic
 

Dark Knight

Founding Member
Feb 1, 2000
2,578
0
0
Chandler, Az.
May 23, 2010
#10
  • May 23, 2010
  • #10
v8only said:
how is it with those 70 primaries? I have the same intake, slightly smaller heads with gt40 aluminums...I upgraded to 68 primaries and it runs rich as hell while cruising now...66's work perfectly for me....I'd bet you have a ton of fumes and it's running rich while cruising??
Click to expand...

But no paxton...
Try pulling the secondary link off and running it. At least it will tell you if the problem is on the primary or secondary side. Sounds to me like the secondary side is going lean.

What fuel pump and regulator?
 

brianj5600

Active Member
Sep 19, 2003
1,964
2
39
Middle TN
May 23, 2010
#11
  • May 23, 2010
  • #11
There is a chart on this page. Holley Performance Products

Different cams have different lift as well as profile like 10sec said. Changing screw holes has an affect too. There are charts that give screw hole differences too. Try google for that.
 
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