holley accelerator pump tunning?

[68dustin]

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]

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]

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]

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]

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.

 

[10secgoal]

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 ?

 

[v8only]

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??

 

[10secgoal]

If you idle speed is set correctly, your jetting should have very little effect on cruising.

 

[v8only]

I agree with that, I was going off topic

 

[Dark Knight]

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??

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]

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.