Holley 750dp lean secondary tip in

[Metalmarty]

Hi All,

I've replaced the Edelbrock 1406 600CFM on my car for a Holley 750 DP and I'm currently trying to jet the holley for optimal performance.
Driving on the primaries is going pretty well, it's drive able.
However, it's going very lean when opening the secondaries and it stays lean for multiple seconds when the secondary boosters seem to kick in.

It's a holley 4150 4779-9 750cfm DP, all new gaskets and ultrasonic cleaned, close to stock.
Floats are set on the car, just below screw openings.
Idle screw 1-1/4 turn open on primaries and secondaries.
Primaries are set to show just a little bit of the transfer slot (square) and secondaries were used to set idle speed, just shy of showing the transfer slot.
Idles at 750rpm.
Primaries: 71 jets, 10.5 Power valve, 35 nozzle and blue cam
Secondaries: 80 Jets, Plugged power valve, 37 nozzle and white cam

Some background information.
I've got a wideband AFR gauge, vacuum gauge and rpm gauge installed.
- Idle vacuum is around 18inhg
- Steady state cruise vacuum is around 21 inhg (steady state 30mph and steady state 50mph)

Idle AFR is around 12.5, leaning it out creates a tip in lean condition on primaries.
Steady state cruise AFR is around 13.5 at 30mph and 50mph.

If secondaries open too fast it lean pops.
If I open secondaries very slow it creeps to 16-17 AFR (shy of lean pop) and after a few seconds it starts to pull fuel out of the boosters, starts to pull hard and WOT afr goes to 12.5-13.0.
So jettings doesn't seem to far off, but I'd like to be able to mash the throttle without it crapping out

Car information.
It's a 1968 Chrysler Newport 4dr HT, weighs 4600 LBS.
- mopar BB 400 ('77 smog era, around 7.5:1 real compression)
- Stock 452 heads
- Edelbrock dp4b intake (aluminium dual plane)
- holley 4150 750 double pumper 4779-9
- mopar performance electronic ignition with blue box from Rick Ehrenberg (waiting for recurve springs from halifaxhops)
- Currently stock .430/.434 cam, but is swapped to a Comp Xe268h cam in the upcoming month
- hedman 78070 headers with 2x 2.5" full dual exhaust with magnaflow mufflers and no crossover
- 2300 stall converter
- 3.23 gears

Does anyone have any tips for me what I can do to get rid of the lean secondaries?

 

[CBODY67]

I will concur, I heard LOTS of customer complaints about the factory Chrysler Holley carbs back then. As the Carters, which replaced them, ran "forever" with NO issues . . . period.

ONE thing back then was the leaking gaskets. The newer gaskets are much better, by observation. I have bought a few newer-spec Holleys and they are installed and have no issues whatsoever. Had to play with the secondary spring to get them to work like I wanted them too, but that's just normal dialing-in, the way I see it.

ONE question I have is "Why a DP on a close-to-stock motor???"

Prior to 1967 or so, Carter had the performance heritage, but Holley came along with their "race" models and took that crown for their own. Holleys are much more tuneable than a Carter, with all of their calibration/orifices which can be changed for particular applications and uses. IF you do not know what you are doing, DON'T.

As for your current settings, there should be about .020" of the primary transition slot showing with the car at hot base idle. Sounds like you do not have that much? Do NOT use the secondary throttle plate adjustment to set the idle speed on the carb. Yet there probably is some hidden-spec setting for this, too. You might go into the Holley website and look for "Tech/Resources" to determine how to adjust the carb properly. NOT like some magazine article might mention. FWIW

OR sell that 4779 to a racer who really needs one and get a new AVS-2 Edelbrock/Carter, using the thick OEM-style base gasket. OR, one of the Summit 4bbls in 750cfm size . . . which is the old Ford 4100 4bbl design and has annular discharge venturis like they had when new, plus a modern electric choke.

Just some thoughts and observations,
CBODY67

 

[furious70]

It seems you're experiencing that your engine isn't able to take advantage of the 750cfm when you want it to. In other words, if you had a vac secondary Holley when you mashed the pedal it wouldn't open the secondaries quickly with the correct spring installed.
Since you have afr measured I would put a bigger and longer secondary pump cam in it (I don't have the colors memorized) and test again.

Also, I believe a stock 4779 would not have 4 corner idle and a rear power valve, do you have a front metering block in the back?

 

[Metalmarty]

There was a reaction before the one of CBODY67, where did it go? I think it was @saforwardlook

I will concur, I heard LOTS of customer complaints about the factory Chrysler Holley carbs back then. As the Carters, which replaced them, ran "forever" with NO issues . . . period.

ONE thing back then was the leaking gaskets. The newer gaskets are much better, by observation. I have bought a few newer-spec Holleys and they are installed and have no issues whatsoever. Had to play with the secondary spring to get them to work like I wanted them too, but that's just normal dialing-in, the way I see it.

ONE question I have is "Why a DP on a close-to-stock motor???"

Prior to 1967 or so, Carter had the performance heritage, but Holley came along with their "race" models and took that crown for their own. Holleys are much more tuneable than a Carter, with all of their calibration/orifices which can be changed for particular applications and uses. IF you do not know what you are doing, DON'T.

As for your current settings, there should be about .020" of the primary transition slot showing with the car at hot base idle. Sounds like you do not have that much? Do NOT use the secondary throttle plate adjustment to set the idle speed on the carb. Yet there probably is some hidden-spec setting for this, too. You might go into the Holley website and look for "Tech/Resources" to determine how to adjust the carb properly. NOT like some magazine article might mention. FWIW

OR sell that 4779 to a racer who really needs one and get a new AVS-2 Edelbrock/Carter, using the thick OEM-style base gasket. OR, one of the Summit 4bbls in 750cfm size . . . which is the old Ford 4100 4bbl design and has annular discharge venturis like they had when new, plus a modern electric choke.

Just some thoughts and observations,
CBODY67

US car parts are not very common here, and a lot more expensive than in the states. A holley carb will set you back well over a grand over here, and its slim pickings. I had a Edelbrock 1406 600CFM on my car which was okay, but I couldn't get rid of a bog when opening the secondaries. Doesn't help that the edelbrock doesn't have an accelerator pump on the secondaries. It has the secondary air door, but they are too light for this application, they shoot open too quick before fuel flows, creating the bog. It was fixable by drilling the air door counter weights and filling them with lead, but I didn't want to go that route.

I could buy the 750 DP for a good price (fraction of new price) so I wanted to try it out.
I admit, in hindsight a 750 vacuum secondaries might have been better for my application. But I'm going to try out a few more modification with my current carb before buying another one.

Holleys are much more tuneable than a Carter, with all of their calibration/orifices which can be changed for particular applications and uses. IF you do not know what you are doing, DON'T.

As for your current settings, there should be about .020" of the primary transition slot showing with the car at hot base idle. Sounds like you do not have that much? Do NOT use the secondary throttle plate adjustment to set the idle speed on the carb. Yet there probably is some hidden-spec setting for this, too. You might go into the Holley website and look for "Tech/Resources" to determine how to adjust the carb properly. NOT like some magazine article might mention. FWIW

I get your consern. But learning is by doing. I'm familiar with Weber IDF carbs and Edelbrock carbs. Holley's are new to me. I don't care if it works right out of the box. I love to figure it all out and finetune carbs like this as good as possible. The vacuum and AFR meters help a lot with this also. This also helps me understand what which circuit is doing in a holley carb. But sometimes it can help to ask some questions in hope that someone points out a small thing I missed or something

I set both primary and secondary slots set to show a square (around .020"). But it would idle rather high. If I would close the primaries more with the screw to lower idle rpm (showing no transfer slot anymore) I would get an off idle stumble. After that I'd reset the transfer slots, and closed the secondaries a bit more to lower idle rpm, I got rid of the off idle stumble, but the secondary lean condition worsened. I reset both primaries and secondaries again to show around .020" of the transfer slot, it would idle around 1000rpm in neutral and around 800rpm in gear.

It would pick-up decent from idle, opening the secondaries was a little less crap, but still way lean.
I've tested if it was a acceleration pump problem or lean jetting. When cruising around opening the throttle too fast (opening the secondaries) would lean it out so much that it backfires through the carb. But if I ease into it very slowly it would get very lean when opening the secondaries, borderlining lean misses, for a few seconds, after which the secondary boosters started flowing and that would bring it down to 12.5-13.0 AFR. Which would indicate that the jetting is fine. I can try a bigger secondary nozzle, but I'm not sure if that's going to help because it takes multiple seconds from opening the secondaries (starting the lean condition) to flowing boosters (bringing the AFR to a nice level again).

It seems you're experiencing that your engine isn't able to take advantage of the 750cfm when you want it to. In other words, if you had a vac secondary Holley when you mashed the pedal it wouldn't open the secondaries quickly with the correct spring installed.
Since you have afr measured I would put a bigger and longer secondary pump cam in it (I don't have the colors memorized) and test again.

Also, I believe a stock 4779 would not have 4 corner idle and a rear power valve, do you have a front metering block in the back?

I admit, in hindsight a 750 vacuum secondaries might have been better for my application. But I'm going to try out a few more modification with my current carb before buying another one.

I've also been thinking of putting a bigger nozzle in the secondaries. I've already swapped the white cam for a blue cam (one of the biggest). Together with the 37 nozzle it should have a pretty big shot, but not enough so it seems. Might have to source some 40 or bigger nozzles to try, not easy to find over here (or crazy expensive).

The 4779-9 came stock with 4 corner idle and no rear power valve. I don't have a power valve in the back, it's just a plug.

 

[CBODY67]

Thanks for the additional information. You realize that you can order Holley carb parts from several sources, EVEN Holley. Summit Racing and Jegs are two vendors and might have the items in stock that you might need. FWIW. Not sure about shipping costs and such, though.

With no secondary power valve, the carb is relying on the secondaries' accel pump to cover any transition lean situations. So the jetting for the secondaries will need to be "power oriented" in nature, I suspect. Meaning about 12.7 AFR when they are operating. Whereas the primaries should be about 14.2 AFR in cruise and 12.7 AFR when the power valve opens. In the pre-ethanol times, cruise would be 14.7 AFR, for reference.

Hot base idle (in "N" or "P") at 1000rpm is TOO fast, period. 700-750 rpm would be better, if possible

In the earlier 1960s hot rod publications relating to Carter AFB carbs, the desire was to get the secondary air valves open sooner by removing weight from the counterweights. Some OEM Chrysler AFBS (as the one which came on my '67 Newport 383 4bbl) had no "secondary air valves", just the secondary throttle valves themselves. Full manual secondaries from the factory. But being about 550cfm, I could floor it from idle and it just went. After cleaning up the casting flash on the venturies, then I could feel a very slight bog when doing that. But nothing significant.

I understand using your "adventures with 4779" as a learning experience and such. Nothing wrong with that, BUT seeking to civilize a race-oriented (by design) carb into a carb which will allow the engine to idle at 600rpm in gear, have good throttle response, and such might be a losing battle. Especially considering the time lag and expense to get specific parts you might need (cut and try) in this venture. There ARE places where the 4-corner idle is good to have. There ARE places where the manual secondary actuation is desired. Even the double-pumper design. BUT I highly suspect YOUR engine is not one of them, unfortunately. BTAIM

Respectfully,
CBODY67

 

[furious70]

With the bigger cam and especially nozzles you may need 50cc pump.
And be on the lookout for a vac secondary

 

[CBODY67]

Regardless of the lean condition, the thing that bothers me is the high base idle. THEN it came to me that the primary throttle plates might have "holes" in them rather than being solid. The particular holes should be adjacent to the idle fuel ports in the carb body.

Those holes are there to allow for more air flow for a good idle with cams which need more air than the normal throttle opening can supply AND still keep the correct relationship between the idle transition slot and the throttle plate at hot base idle. So, those holes could explain why the hot bse idle is so high with the transition slot relationship being maintained.

Therefore, as an experiment, you might get some strong duct tape (soft and burnable, if it should go somewhere) and lay to dots over the holes in the carb primary throttle plates. IF you can then get the idle speed back to normal that way, then the experiment has been successful. Then you can proceed to either get new solid throttle plates or solder the holes shut (dressing them down so they are smooth). If the hot base idle goes too low, then you can use a small drill to open the holes back up a bit in the tape, to approximate the size needed for sufficient idle air flow additiona. This proceedure usually happens in reverse, adding holes of a particular size rather than closing them down. It is mentioned in both the HPBooks and S-A Design Holley carb books. Should be in the tech/resources/tuning-adaptation sections of the Holley website, too, probably.

The 4779 might not be the best carb for your application, but it should still at least idle in the 700rpm range, I suspect.

Hope this might help,
CBODY67

 

[Knebel]

I didnt read through 100% of the posts, does your holley have adjustable idle bleeds? The lean tipin if you lean out the idle could be solved with smaller bleeds. You can rry that by taking thin copper wire and putting it in the bleed, attach it somwhere so it get sucked in. Try to play with the pump cams, find one that has a profile that gives lots of pump movement right off the opening.

 

[70bigblockdodge]

Pull the rear float bowl and adjust the clearance for the check ball, for the accelerator pump. You need .011 as spec, usually a lot more. If it is a rubber disc for check valve you may have to replace it. It is delaying the pump shot by pushing fuel back into float bowl.

 

[Metalmarty]

Thanks for the additional information. You realize that you can order Holley carb parts from several sources, EVEN Holley. Summit Racing and Jegs are two vendors and might have the items in stock that you might need. FWIW. Not sure about shipping costs and such, though.

With no secondary power valve, the carb is relying on the secondaries' accel pump to cover any transition lean situations. So the jetting for the secondaries will need to be "power oriented" in nature, I suspect. Meaning about 12.7 AFR when they are operating. Whereas the primaries should be about 14.2 AFR in cruise and 12.7 AFR when the power valve opens. In the pre-ethanol times, cruise would be 14.7 AFR, for reference.

Hot base idle (in "N" or "P") at 1000rpm is TOO fast, period. 700-750 rpm would be better, if possible

In the earlier 1960s hot rod publications relating to Carter AFB carbs, the desire was to get the secondary air valves open sooner by removing weight from the counterweights. Some OEM Chrysler AFBS (as the one which came on my '67 Newport 383 4bbl) had no "secondary air valves", just the secondary throttle valves themselves. Full manual secondaries from the factory. But being about 550cfm, I could floor it from idle and it just went. After cleaning up the casting flash on the venturies, then I could feel a very slight bog when doing that. But nothing significant.

I understand using your "adventures with 4779" as a learning experience and such. Nothing wrong with that, BUT seeking to civilize a race-oriented (by design) carb into a carb which will allow the engine to idle at 600rpm in gear, have good throttle response, and such might be a losing battle. Especially considering the time lag and expense to get specific parts you might need (cut and try) in this venture. There ARE places where the 4-corner idle is good to have. There ARE places where the manual secondary actuation is desired. Even the double-pumper design. BUT I highly suspect YOUR engine is not one of them, unfortunately. BTAIM

Respectfully,
CBODY67

I know that I can order them from summit etc. But if I buy say a $500USD carb, shipping will be around $150USD. When it gets here I have to pay 21% tax and 4.2% over 650$USD with some administration fees. Turning a $500USD carb into north of $850USD, which sucks... Same with all other stuff I have to order from the states.

But you are correct. The DP is probably not for me. I'm looking around for a affordable vacuum secondary carb. If not I might look around if I can order a Brawler 4150 vacuum secondary, 670CFM, seems like a nice size. They also have them in 770CFM size. Brawler BR-67256 670 CFM Brawler Diecast Carburetor Vacuum Secondary
I found a lot of great reviews on the Brawler carbs, with a lot of adjustability too.

With the bigger cam and especially nozzles you may need 50cc pump.
And be on the lookout for a vac secondary

Good to know. Is that .040" and up, or even bigger nozzles? I do know that you need hollow screws around .040" and up nozzles.

And I am, also seem my reaction a few lines up

Regardless of the lean condition, the thing that bothers me is the high base idle. THEN it came to me that the primary throttle plates might have "holes" in them rather than being solid. The particular holes should be adjacent to the idle fuel ports in the carb body.

Those holes are there to allow for more air flow for a good idle with cams which need more air than the normal throttle opening can supply AND still keep the correct relationship between the idle transition slot and the throttle plate at hot base idle. So, those holes could explain why the hot bse idle is so high with the transition slot relationship being maintained.

Therefore, as an experiment, you might get some strong duct tape (soft and burnable, if it should go somewhere) and lay to dots over the holes in the carb primary throttle plates. IF you can then get the idle speed back to normal that way, then the experiment has been successful. Then you can proceed to either get new solid throttle plates or solder the holes shut (dressing them down so they are smooth). If the hot base idle goes too low, then you can use a small drill to open the holes back up a bit in the tape, to approximate the size needed for sufficient idle air flow additiona. This proceedure usually happens in reverse, adding holes of a particular size rather than closing them down. It is mentioned in both the HPBooks and S-A Design Holley carb books. Should be in the tech/resources/tuning-adaptation sections of the Holley website, too, probably.

The 4779 might not be the best carb for your application, but it should still at least idle in the 700rpm range, I suspect.

Hope this might help,
CBODY67

My 4779 doesn't have holes in them, but I do know what you mean.
I can get it to idle perfectly fine down at 700rpm. The problem is that either my primary transfer slot is not visible anymore if I use the primary throttle screw, causing a lean tip in from Idle when opening the throttle. Or my secondary transfer slot is not visible when using the secondary throttle screw to lower idle, which worsens my lean condition when the secondaries open.

I didnt read through 100% of the posts, does your holley have adjustable idle bleeds? The lean tipin if you lean out the idle could be solved with smaller bleeds. You can rry that by taking thin copper wire and putting it in the bleed, attach it somwhere so it get sucked in. Try to play with the pump cams, find one that has a profile that gives lots of pump movement right off the opening.

No adjustable idle bleeds unfortunately. Thanks on the tip with the smaller bleeds. I might try the thin wire truck, see if that helps.

Pull the rear float bowl and adjust the clearance for the check ball, for the accelerator pump. You need .011 as spec, usually a lot more. If it is a rubber disc for check valve you may have to replace it. It is delaying the pump shot by pushing fuel back into float bowl.

This is one of the later versions of the 4779, It doesn't have the check balls anymore. It has the rubber one way valve for pulling fuel in and it only has the check needles directly underneath the accelerator nozzle.

 

[70bigblockdodge]

This is one of the later versions of the 4779, It doesn't have the check balls anymore. It has the rubber one way valve for pulling fuel in and it only has the check needles directly underneath the accelerator nozzle

The rubber disc may have something stuck under it or just be not sealing. How much did it sit?

 

[furious70]

Whether you need a 50cc pump can be tested with the pump cam you have, if you go from idle to wot do you drain the reservoir before the cam returns the arm to rest?

 

[Metalmarty]

The rubber disc may have something stuck under it or just be not sealing. How much did it sit?

It's sealing well and doesn't have anything stuck underneath it. The rubber disc is a couple weeks old. I ultrasonic cleaned and rebuild the carb.

Whether you need a 50cc pump can be tested with the pump cam you have, if you go from idle to wot do you drain the reservoir before the cam returns the arm to rest?

Good to know. It doesn't drain the reservoir at the moment.




I just got a message that someone I know is going to travel to the states. So I might have him pick up a new vac secondary carb for me while he is there. Waaaay cheaper than getting one over here.

I'm looking at the brawler 4150 line of carbs. They seem to work very very well well and have a lot of adjustment to them. Any tips?

And the vac secondary brawlers are available in 670 and 770 CFM. I'm thinking of getting the 670cfm one. Or should I get the 770CFM to go with the XE268H cam later.

 

[furious70]

When on the fence on size for vac secondary carb I say always go bigger, it'll only open up as much as needed

 

[Metalmarty]

I've broken the bank and I've bought a Brawler BR67256.
670CFM vacuum secondary with lots of adjust-ability.

Works way better out of the box, but still has a high load lean spot.
I've opened a new thread.
Lean AFR for multiple seconds on high load (Brawler 670cfm vac)

Hopefully I can get it figured out