Holley Carb Tuning help on a 4412

Rooster34

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Hey guys and girls hope all is well in your neck of the woods! So let me start off in my journey with my 65 Plymouth FuryII 4 door. It has the 318npoly a series engine, I rebuilt it last year and put a 264 .450 cam in it all the other internals are standard and the block was only honed. I kept the 2bbl stock intake and replaced the carb with a holley 4412 500 cfm 2 bbl which I rebuilt with the holley trick-kit. I kept the standard jets which are 73H updated the power valve to a 10.5 and now has a tubed 45 squiter. The idle screws and accelerator pump are all adjusted to spec. The accelerator pump cam is the red one and in the #1 position. When I punch it from a stop she stalls right out. I'm not sure if I need some different carb cams or adjust the position of the one that's in there right now or keep going up in the squiter size I have a 47, 50, 55 and a 63 on order which are the straight shot squirters. My timing is at 38 all in at 3000 rpm any help with tuning this is greatly appreciated!
 

70bigblockdodge

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If it is a older model check the check ball clearance for the accelerator pump. If it's newer make sure the sealing surface is smooth for the rubber check valve to seal well.
 

CBODY67

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As the throttle bores on that carb are bigger than the orig 2bbls', it might be that for that smaller motor, the idle plates are closed a bit too much at idle. Look at how much of the transition slot is below where the idle plates are at idle. There is a design "sweet spot" of how much of that port should be uncovered, for good off-idle response, at hot base curbe idle. To little exposed, a flat spot. Too much, doesn't work well either. I would suspect that the larger cam would need more air at idle to kind of even things out.

What did it take to adapt your Holley 2bbl to the stock intake manifold?

Is the issue at hot base idle or more when the carb is on fast idle when cold? Just curious.

Just some thoughts,
CBODY67
 

Rooster34

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Mine uses the rubber umbrella type diaphragm and is sealed wel, I get good fuel coming from the squirter. I may try and move the cam to position #2 and see what that does. I should get my bigger squirters in the next few days and see what those do. Also I do have the screw installed that has the hole in it for the 40 and bigger squiter sizes.
 

Rooster34

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As the throttle bores on that carb are bigger than the orig 2bbls', it might be that for that smaller motor, the idle plates are closed a bit too much at idle. Look at how much of the transition slot is below where the idle plates are at idle. There is a design "sweet spot" of how much of that port should be uncovered, for good off-idle response, at hot base curbe idle. To little exposed, a flat spot. Too much, doesn't work well either. I would suspect that the larger cam would need more air at idle to kind of even things out.

What did it take to adapt your Holley 2bbl to the stock intake manifold?

Is the issue at hot base idle or more when the carb is on fast idle when cold? Just curious.

Just some thoughts,
CBODY67

I used the trans dapt 2040 adapter. The carb has a manual choke and I hardly use it, but yes it happens when engine is cold and warmed up. Curb idle in park and neutral is 975-1025 and in drive is about 675-700 ish. I have played with the idle screws and they are where they should be, I can play with my curn idle screw to up the idle and then re-adjust my accelerator pump arm. I just don't want to go to high with the idle as to harm the trans when shifting from park to reverse to drive
 

Dana

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Where does 38 total put your timing at idle?
 

CBODY67

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Thanks for the information on idle speed. I suspect that is where the stumble might be coming from. I highly suspect your current idle speed is too high, which makes the throttle plates toward to upper end of the transition slot in the throttle bore.

While the specs on that cam don't seem too wild, for a (basically) 5 litre-size engine, they are wilder than they would be if in a 5.9L engine.

While I still had the orig 305 in my '77 Camaro, ti upgraded the cam to a "266 Energizer" Cam Dynamics cam (210 degrees @ .050" lift and .440" lift). I also installed a Holley 28-Z intake and an emissions-spec 4160 (1.56" throttle bore, 600cfm) carb. I had no issues with setting the idle at about 650rpm in "N". In "D", it went down a bit but was smooth. I never was really comfortable with the idle speed and mixture. I took it to work and hooked it up to the BIG Sunn machine to check afr and such. I never could get it as lean as Holley said was possible, as when I got the HC down to their specs, the HC figures went bananas, changing to wildly different readings as soon as the digital display could display them. Lean Misfire is what I was seeing.

The particular power valve in that carb was an emissions-oriented "two-stage" power valve. First stage came in at 10"Hg and the second (full) stage at the normal 5.5"Hg. Interestingly, in "D" with the a/c on, idle vac was 10.5"Hg. Just barely above when the power valve would start to open. When I did add just enough throttle in "D" to get it to start to open, it was not a big enrichment, but just a bit. Still, I wanted it closed in those situations.

So, I would suggest that you drop the hot base idle speed down to about 700rpm in "N"/"P" and see how things might change. Re-adjust the idle mixture screws at that speed, too. Plus verify the base ignition timing as you might also be getting a few degrees of advance at that earlier/higher idle speed, too. If your off-idle throttle issues are diminished, then we're on the right track.

IF things improve, then you might try my shadetree method of idle speed adjustment. Decrease the hot base idle speed until you can feel individual pulses at the end of the tail pipe, then add another 25rpm until they just smoooth out. This is with the car in "D" with the parking brake firmly applied, headlights on "Bright" and a/c, if equipped, operating. When things just smooth out, then optimize the idle mixture at where the idle speed goes to in "N"/"P". If that works as well as it did on one of our vehicles, it should result in a smooth and stable hot base idle speed.

Just some thoughts,
CBODY67
 

Rooster34

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Going to take a video for yall and go over everything thing hopefully be better than typing!
 

Rooster34

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Thanks for the information on idle speed. I suspect that is where the stumble might be coming from. I highly suspect your current idle speed is too high, which makes the throttle plates toward to upper end of the transition slot in the throttle bore.

While the specs on that cam don't seem too wild, for a (basically) 5 litre-size engine, they are wilder than they would be if in a 5.9L engine.

While I still had the orig 305 in my '77 Camaro, ti upgraded the cam to a "266 Energizer" Cam Dynamics cam (210 degrees @ .050" lift and .440" lift). I also installed a Holley 28-Z intake and an emissions-spec 4160 (1.56" throttle bore, 600cfm) carb. I had no issues with setting the idle at about 650rpm in "N". In "D", it went down a bit but was smooth. I never was really comfortable with the idle speed and mixture. I took it to work and hooked it up to the BIG Sunn machine to check afr and such. I never could get it as lean as Holley said was possible, as when I got the HC down to their specs, the HC figures went bananas, changing to wildly different readings as soon as the digital display could display them. Lean Misfire is what I was seeing.

The particular power valve in that carb was an emissions-oriented "two-stage" power valve. First stage came in at 10"Hg and the second (full) stage at the normal 5.5"Hg. Interestingly, in "D" with the a/c on, idle vac was 10.5"Hg. Just barely above when the power valve would start to open. When I did add just enough throttle in "D" to get it to start to open, it was not a big enrichment, but just a bit. Still, I wanted it closed in those situations.

So, I would suggest that you drop the hot base idle speed down to about 700rpm in "N"/"P" and see how things might change. Re-adjust the idle mixture screws at that speed, too. Plus verify the base ignition timing as you might also be getting a few degrees of advance at that earlier/higher idle speed, too. If your off-idle throttle issues are diminished, then we're on the right track.

IF things improve, then you might try my shadetree method of idle speed adjustment. Decrease the hot base idle speed until you can feel individual pulses at the end of the tail pipe, then add another 25rpm until they just smoooth out. This is with the car in "D" with the parking brake firmly applied, headlights on "Bright" and a/c, if equipped, operating. When things just smooth out, then optimize the idle mixture at where the idle speed goes to in "N"/"P". If that works as well as it did on one of our vehicles, it should result in a smooth and stable hot base idle speed.

Just some thoughts,
CBODY67
So I got the idle nice and smoothed out, I think you were right with my curb idle being a bit too high and those small slots being exposed. I'm idling at about 950 now in P/N and around 650 in D that's with no high beams or lights on. I replaced the squirter with a 63 and I still get that stall from a dead stop when I punch ibut it seems to be coming out of a smidge bit. I'm wondering if I should play around with some pump cams to see if I can get a bigger shot in there.
 

Dana

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Sounds good
 

Dana

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Let’s discuss your method of valve adjustment.?
 

Rooster34

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Let’s discuss your method of valve adjustment.?
I adjust the valves cold that way when the warm up they have the correct lash. I can check it today when I get home and readjust if needed
 
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Dana

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I think that the .015 that your card uses is on the tight side to begin with.
 

Dana

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What happen here???????
 

Rooster34

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I think that the .015 that your card uses is on the tight side to begin with.
What would you recommend? I have the lash set cold at .012 right now. My tappets are a little loud because I reused the original rockers and push rods.
 

Dana

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By nature solids are going to make more noise than hyd. First note your vacuum at the .012 cold setting. Note it with engine cold and engine hot. Then readjust to .024 cold and note the vacuum hot and cold. If you see an improvement then you can play with tighter settings especially on the intake side.
 

Rooster34

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***PROBLEM SOLVED***
So I got the stall issue figure out about a week ago, I ended up getting the yellow pump cam which is the most aggressive and only 1 of 2 options for the 50cc accelerator pump and I already had the brown one on. What the yellow pump cam does is let the whole contents of the 50cc pump out and squirt into the carb. I ended up swapping out the 63 squirter I had in there once I replaced the pump cam with the yellow one to a 55 squirter. The 63 was a but rich and would throw some smoke when I stabbed the gas. I may drop to a 50 and see what that does but so far so good and no more stalling!!
 
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