Carb tuning, accelerator pumps.

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moparmanestock

moparmanestock

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I keep trying to make gains on my car, it's never perfect, right.
The next step I want to improve is my car's reaction when the gas is mashed. There is a little bit of lag right now, I want to get rid of it. It's killing my reaction time.
So the question: How do you set up your Acc pump cam and linkage? Mine has a bit of play from the pump arm to the spring bolt on the linkage. what do you guys set the gap at?
Also, not sure what to try to change the cam and position of cam to improve. Any suggestions? This is a ProForm 750 Holley.
 
A good base line is: White cams #2 spot, no play, #31 suirters. IMO
 
that gap should be set at wide open throttle.
No gap should be there at idle.
Not sure on a proform, but the holley''s are about. 015 .
 
Mike 340 said:
that gap should be set at wide open throttle.
No gap should be there at idle.
Not sure on a proform, but the holley''s are about. 015 .
Click to expand...
Agree.
The other thing to check is that the arm is touching at idle - no slop. some pump cams require a slight rework of the arm (assuming yours has a metal arm).

PS If there is delayed response when opening the throttle very slowly, then its the idle circuit needs adjusting.
 
Jet up 2 sizes, make pass after pass till the MPH drops off then go back 2 jet sizes. For Pump shot do the same with squirter till the 60' drops off or it starts to blow black out the back then go back 2 sizes.
 
What nozzle? If you have a 30cc pump you get 30cc's whether you got a 25 or a 45 nozzle, with a 25 you get less fuel for a longer period of time, with a 45 you get more fuel for a shorter period of time.
 
Most applications will work with a 30 CC pump. if its a race car application i would say go to a 50 CC pump.
 
I have never left a .015 gap at the pump. I set it to zero. There is no reason not to. Some engineer got his panties wadded up about pushing the diaphragm over center. Years ago, I spent a bunch of time measuring stuff. You will coil bind the diaphragm spring before you kill the diaphragm itself.

So.....set your accelerator pump with zero clearance at wide open with this cam you are using. If you are foot braking, or using a stick, be prepared to START with a 37 squirter and go bigger until it cleans up the bog. You will need the big pump screw so the screw isn't the limit.

Working with a foot braked front engine dragster that went 8.3XX we needed a full 1/16 squirter (.0625) hole to make it leave. It wanted a butt load of fuel in a short time.

As stated above....smaller squirter is less fuel over a longer time period. Bigger squirter is more fuel over less time.

Some combinations want a ton of fuel right away. Give it what it wants.
 
moparmanestock said:
I keep trying to make gains on my car, it's never perfect, right.
The next step I want to improve is my car's reaction when the gas is mashed. There is a little bit of lag right now, I want to get rid of it. It's killing my reaction time.
So the question: How do you set up your Acc pump cam and linkage? Mine has a bit of play from the pump arm to the spring bolt on the linkage. what do you guys set the gap at?
Also, not sure what to try to change the cam and position of cam to improve. Any suggestions? This is a ProForm 750 Holley.
Click to expand...

You can see it go lean with a wideband when the throttle is mashed. I have three accelerator pumps on my six pack, and using a wideband makes things so much easier to dial them in. Seat of the pants helps, but using a wideband is a no brainer for tuning. Data logging with a TPS and a tach feed is even better.
 
Thank you all. I have been jetting the car up by 2s, 3 time and keeps going faster. I will take the play out of the linkage and set it at WOT. Sounds like it also wants a larger nozzle, will try that too.
 
sometimes if you have to keep increasing the jet size....your fuel system may not be able to provide the volume that is needed...hence it is running out of fuel in high gear.
 
Keep in mind that depending on the accelerator pump cam, you may not even be getting all 30cc of fuel. The different pump cams not only have different rates, but different max lifts as well, which equates to volume of the shot.
 
No play in pump arm, 30cc pumps, 31 squirters. If car hesitates when snapping throttle open, increase squirter size OR pump cam ramp. If car puffs and feels a little soggy down low, go to a smaller squirter like a 28 OR a milder pump cam ramp. It is trial and error. Heavy cars and/or not enough converter/gearing are MUCH pickier about the accelerator pump.

Something to thing about! If you leave at say, 2000 rpm your car is NOT leaving off of idle and you have already used up some of the pump arm travel because the throttle is partially open! You CAN adjust it from there so you get the full pump shot. Yes, it will hesitate around the pits off of idle but WHO CARES if it is a race car.
 
Mopar-Man said:
No play in pump arm, 30cc pumps, 31 squirters. If car hesitates when snapping throttle open, increase squirter size OR pump cam ramp. If car puffs and feels a little soggy down low, go to a smaller squirter like a 28 OR a milder pump cam ramp. It is trial and error. Heavy cars and/or not enough converter/gearing are MUCH pickier about the accelerator pump.

Something to thing about! If you leave at say, 2000 rpm your car is NOT leaving off of idle and you have already used up some of the pump arm travel because the throttle is partially open! You CAN adjust it from there so you get the full pump shot. Yes, it will hesitate around the pits off of idle but WHO CARES if it is a race car.
Click to expand...

Makes sense to me. May try that as well. I don't know what the shooter sizes are right now. I does have 1 30cc and 1 50cc pump. The main issue does seem to be leaving off the start, a moments hesitation, and then its on.
 
70aarcuda said:
sometimes if you have to keep increasing the jet size....your fuel system may not be able to provide the volume that is needed...hence it is running out of fuel in high gear.
Click to expand...
If that was the case, would I see a pressure drop fuel on the top end? I haven't been watching that.
 
Pump adjustment has always been to set it so that at full shot there is only .015 more moment of the diaphragm before bottoming out.
I have seen cases of people flubbing the adjustment loose to compensate for too much cam or squirter size.
 
Mopar-Man said:
No play in pump arm, 30cc pumps, 31 squirters. If car hesitates when snapping throttle open, increase squirter size OR pump cam ramp. If car puffs and feels a little soggy down low, go to a smaller squirter like a 28 OR a milder pump cam ramp. It is trial and error. Heavy cars and/or not enough converter/gearing are MUCH pickier about the accelerator pump.

Something to thing about! If you leave at say, 2000 rpm your car is NOT leaving off of idle and you have already used up some of the pump arm travel because the throttle is partially open! You CAN adjust it from there so you get the full pump shot. Yes, it will hesitate around the pits off of idle but WHO CARES if it is a race car.
Click to expand...
My 340 had a slight stumble leaving at 2K. Tried different cams and nozzles and no fix. Went back to 31 nozzles and set pink cam up front #2 cam hole/#2 throttle hole, readjusted pump travel. Secondary is pink #1. Launches clean.
 
On my street/strip 340 (4.30's/4200stall/.590 solid cam) we ran an 850DP which was 2/10ths quicker in the 1/4 than a 750DP, it was ok off the hit, no stumble but felt a bit weak so we installed a 50cc front pump, pink cam and 35 extended shooters, was noticeably stronger on the hit and you could feel the difference on the street as well.
 
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