daer0

New Member
May 16, 2021
8
0
1
36
Canada
Hey,

I'm looking for some tips after rebuilding my holley double pumper. When I stomp on the pedal (idling) the car will sputter and if I press moderately it will spit fire out the primary and air out the secondary. If I press the gas gradually, there's no issues and it revs as expected. It does while driving but a bit less so. I set the pumps to "factory position" Where they're just about pressing gas through on. Basically, as soon as I blip the throttle, they squirt. The throttle cam is in position 1 with the white insert. The nozzles I believe are the stock ones, I tried putting larger but it just lit on fir in the primary (won't be going back to that shop anymore... idiots).

I do have two other issues:
- The fuel mixture screws won't affect the vacuum unless they're removed entirely.
- Idle RPM is high once warm. 600 cold and 1100 when warm. Warm or cold, in gear is 550.

- I've rebuild the carb with a holley trick kit.
- Installed new MSD cables
- Installed 2x silver (light) springs and red bushing on the MSD distributor
- Clean the contacts for the cables under the cap
- Checked for leaks by choking out the carb; It dies quickly when I cover the carb
- The vacuum sits at around -13-15
- Set the initial timing to 6° (stock)
- Redid the seal on the intake manifold when swapping to an edelbrock performer
- Fuel bowls are set to trickle a little gas out the sight holes if I rock the car good enough
- Throttle plate gap set to where the idle gas slot is squared

My setup:
1972 Mach 1
351c w/ 2v heads
Holley 4150 750 classic double pumper w/ electric choke (p/n: 0-4779CE)
MSD ignition kit: 6AL controller with MSD distributor, coil and cables

Banging my head up against the wall. What'd I miss?
 
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HemiRick

I'd be looking at jacking under the house
Jun 28, 2020
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If fire is getting into the intake/carb, the timing is way way off or you have an intake valve not sealing or closing all the way, and allowing combustion into the intake.
 
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daer0

New Member
May 16, 2021
8
0
1
36
Canada
Eh.... the valves appear to have full relief movement. If it was a bent valve it'd be rough too. This isn't a constant or persistent issue, it's only when stepping on the gas. It's not like the valve is only failing to seal when I hit the gas *just* enough.
 

7991LXnSHO

wanna catch the space herp
10 Year Member
Sep 1, 2010
5,261
1,672
194
Kearney, NE
@HemiRick has two viable suggestions. Two more are vacuum leaks, the vac advance is hooked up to the wrong port, thee is some MSD issue, or you missed something in the rebuild.
Pick your favorite and start checking it out.
 

daer0

New Member
May 16, 2021
8
0
1
36
Canada
@HemiRick has two viable suggestions. Two more are vacuum leaks, the vac advance is hooked up to the wrong port, thee is some MSD issue, or you missed something in the rebuild.
Pick your favorite and start checking it out.
Again, a bent valve not sealing is not my problem or again, it would be a consistent issue. Further, I wouldn't get good compression on the cylinder it'd be in.

I don't have a vac advance, it's a bullet distributor. There is no MSD issue as it's been tested fine. I didn't miss something in the rebuild. All parts are on the Holley.

Thank you though.
 
Last edited:

7991LXnSHO

wanna catch the space herp
10 Year Member
Sep 1, 2010
5,261
1,672
194
Kearney, NE
So what answer do you want? We can tell you how to retrofit EFI and recommend it if you have a significant other who needs convinced of the price.
That the mixture screws do not change vacuum is a strong indicator for a vac leak (hose, carb base gasket, intake gasket), or the carb has a problem like a clogged passageway. The wrong power valve can do bad things
But apparently without more info on your setup and willingness to double check what you missed, it’s a problem.


11BC83B3-7385-47AA-9056-179C5F786F61.png
 

daer0

New Member
May 16, 2021
8
0
1
36
Canada
So what answer do you want? We can tell you how to retrofit EFI and recommend it if you have a significant other who needs convinced of the price.
That the mixture screws do not change vacuum is a strong indicator for a vac leak (hose, carb base gasket, intake gasket), or the carb has a problem like a clogged passageway. The wrong power valve can do bad things
But apparently without more info on your setup and willingness to double check what you missed, it’s a problem.


11BC83B3-7385-47AA-9056-179C5F786F61.png
Sorry you guessed wrong and I double checked certain things? Also stop making assumptions about me it's only making an ass out of you.

Speaking of which, the only "askhole" here is you bud. I'm discussing why it's not a bent valve. Don't see why you're so pissed off that I don't have the symptoms of it. I also don't see why you're so pissy I checked for and found no vacuum leaks.

There's plenty of info about my setup, you're just choosing to ignore most of it. You need to revaluate your responses or not respond when you're so cranky.
 
Last edited:

7991LXnSHO

wanna catch the space herp
10 Year Member
Sep 1, 2010
5,261
1,672
194
Kearney, NE
Apparently your sense of humor is also misfiring or not warped enough. :jester:

So seriously, MSD stands for Suddenly May Die around here. So if the valve is not bent, the fire or spark is coming from somewhere. Is it cross firing some wire, is it a cap and rotor issue (carbon trace or crack), is the box malfunctioning?
You need to be willing to check and recheck some things. The first answers, particularly the first serious one, is most often the right one or at least the right general idea.
Good luck. I’ll get some coffee to be less grumpy while you check out the ignition.
 

daer0

New Member
May 16, 2021
8
0
1
36
Canada
Apparently your sense of humor is also misfiring or not warped enough. :jester:

So seriously, MSD stands for Suddenly May Die around here. So if the valve is not bent, the fire or spark is coming from somewhere. Is it cross firing some wire, is it a cap and rotor issue (carbon trace or crack), is the box malfunctioning?
You need to be willing to check and recheck some things. The first answers, particularly the first serious one, is most often the right one or at least the right general idea.
Good luck. I’ll get some coffee to be less grumpy while you check out the ignition.
Rather than giving attitude (then later trying to dismiss it as humor) say what info you need more of.

Then again, giving you more info about how it isn't exhibiting certain symptoms of the suggestion just made you upset anyways :shrug:

Also, it'd be a smarter approach to the issue to understand the problem and setup better than try to swing a sledgehammer in the dark by saying "retrofit an EFI system" based off your bias.
 

Mustang Phil

Member
Mar 4, 2021
4
4
13
65
Saugerties, N.Y.
Hey,

I'm looking for some tips after rebuilding my holley double pumper. When I stomp on the pedal (idling) the car will sputter and if I press moderately it will spit fire out the primary and air out the secondary. If I press the gas gradually, there's no issues and it revs as expected. It does while driving but a bit less so. I set the pumps to "factory position" Where they're just about pressing gas through on. Basically, as soon as I blip the throttle, they squirt. The throttle cam is in position 1 with the white insert. The nozzles I believe are the stock ones, I tried putting larger but it just lit on fir in the primary (won't be going back to that shop anymore... idiots).

I do have two other issues:
- The fuel mixture screws won't affect the vacuum unless they're removed entirely.
- Idle RPM is high once warm. 600 cold and 1100 when warm. Warm or cold, in gear is 550.

- I've rebuild the carb with a holley trick kit.
- Installed new MSD cables
- Installed 2x silver (light) springs and red bushing on the MSD distributor
- Clean the contacts for the cables under the cap
- Checked for leaks by choking out the carb; It dies quickly when I cover the carb
- The vacuum sits at around -13-15
- Set the initial timing to 6° (stock)
- Redid the seal on the intake manifold when swapping to an edelbrock performer
- Fuel bowls are set to trickle a little gas out the sight holes if I rock the car good enough
- Throttle plate gap set to where the idle gas slot is squared

My setup:
1972 Mach 1
351c w/ 2v heads
Holley 4150 750 classic double pumper w/ electric choke (p/n: 0-4779CE)
MSD ignition kit: 6AL controller with MSD distributor, coil and cables

Banging my head up against the wall. What'd I miss?
what do the plugs look like maybe running lean
 

daer0

New Member
May 16, 2021
8
0
1
36
Canada
what do the plugs look like maybe running lean
I actually went through a bunch of stuff since this post and found I have trouble with two pistons firing late or early. You can see the carbon deposits on the channels through the intake to piston 8 and 3 if memory serves.

I haven't looked at it since as I'm focused on my other car but the plugs are all different, some are good but others are soothed or wet. I have a new set to put in but for now it's on hold.

It's not a lean condition I'm sure of that. If I go any higher on the jets or squirters I'm get fire in the carb.

So pre-det maybe due to bad cable, plug or valve?
 

HemiRick

I'd be looking at jacking under the house
Jun 28, 2020
764
288
73
58
Memphis TN
on 2nd reading of your 1st post, this could also be a too small acc. pump shot....a lean backfire when given throttle too quickly.
 

7991LXnSHO

wanna catch the space herp
10 Year Member
Sep 1, 2010
5,261
1,672
194
Kearney, NE
I’ve been wondering if the timing set at 6 deg before or after TDC?
The two cylinders firing off could be because of bad ignition components or or the wires set to the wrong firing order. You can fix both with a tune up, I hope.

As far as the carb, I was hoping this no longer an issue.
I set the fuel level just below the sight holes on the Holleys, so a little will come out if the car is rocked.
I had a new carb that the o ring was cut by poor machining on the bowl. I was able to set it so it was just over the hole’s edge, but it was a controlled leak with the needle almost fully shut off, and ran poorly under acceleration.