Holley 750 CFM Ultra Double Pumper or Quick Fuel Technology SS-750-AN 750 CFM Street?

[RedHawk]

....or other carb hell I don't care. This is all I can find that makes some sense to me.

Full disclosureI know only enough to be super dangerous.)
What Carb to go with. Don't care about gas mileage just want to get all I can out of this engine before it explodes and I get a BBF FE.

I have a 351w with Performer RPM heads #6025.
410 gears
I am in Colorado at a starving 5000 ft.
Recently ran Banidimere and wothout power shifting ran a 13.7 qtr mile,
I also run the car on road courses too so not just a drag car in fact more of a track car and street.
170cc
Intake valve 2.02"
exahust 1.6"
Edledbrock spec sheet says to use a 750cfm carb.
cam is a #7182 rpm range 1500-6500 and very lopey.
1:6:1 roller rocker arms
duration .004 lift 290 and 30
lift cam intake .310 and .325
Monkey garage idiots took off edlebrock 750cfm carb and put an avenger 570cfm carb on it and it runs like dog sh%t. stumbles at WOT at around 5000 rpms.

I recently hacked off the 1" inlet glasspacks and replaced with jones exhaust 3 1/2 inlets and the exhaust sounds and feels beautiful but problem is when secondary's kick in the car pulls nicely and then sputters at 5000 rpms.

I know there are a hand full of things to do but I figured with edlebrock specifying the 750cfm carb and the newly free flowing exhaust I should increase the cfm on the carb.

Thoughts?

[blykins]

You need one of my custom Quick Fuel Q-750's, setup for your engine and elevation.

[RedHawk]

Blykins-

I know your one of the resident engine experts on the forum and at the appropriate time I will be contacting you when I plan on changing engines, but for now I am definitely interested in one of your custom tuned QF.
I'll send a pm.
I am in a little time crunch having a couple races coming up. You can tell me lead times when we talk
Thanks

[Karl Bebout]

Redhawk, From Bret's reputation on this forum, I'd have no doubt about his carb work. However, Patrick, at ProSystems builds carbs customized specifically for your car. He's been doing it for years and I've had two of his carbs that were outstanding to the point that a couple of my friends also bought his carbs and were totally happy with them. I have not used Bret's carbs and perhaps he too, builds them specifically and has a flow bench and such, but like I said. I was totally blown away with my ProSystems carbs. Just my 2¢ worth.

[blykins]

Originally Posted by Karl Bebout

I have not used Bret's carbs and perhaps he too, builds them specifically and has a flow bench and such.....

Yes sir, we build them individually. They are not off the shelf pieces.

[RedHawk]

Originally Posted by blykins

Yes sir, we build them individually. They are not off the shelf pieces.

So Blykins I reached out to Scott but no answer.
Here's the situation and what I sent to Scott.

Scott hope your enjoying Football Sunday. Its Scotty from Colorado who has a carb from Blykins for my supercharged cobra. I have relocated to Dallas Texas and want to adjust carb for the altitude, humidty temp etc. I have attached the build card that came with carb. In Co the carb was running super rich so I backed jets of to pri 74 and sec to 84. Car ran better.

Here in Dallas the car runs decent until highway speeds where it seems to sputter when hitting throttle. Any suggestions are super appreciated.

Attached is a picture of one of the plugs.

Thanks.

Btw, the car pulls like a bat out of hell from 1st to 4th. So much so I haven't gone above 4500 because I feel like wheels are going to break loose for good.

When cruising at highway speed in 5th and pressing accelerator the car hesistates. If I drop into 4th then car seems to steady out of hesitation.
Fuel pressure is consistent at 6 to 6.5.
Car idles at around 900 to 1000.
Timing is at 36 and seems best setting.
Colder plugs and correct gap set.

Thoughts?

Move to PV 6.5(dependent on vacuum pressure?
Increase sec jet back to 86 or beyond?

Also not to put you on the spot but in a general sense what does Scott actually do with these carbs that the factory doesn't already do? I ask because the build card looks to be exact to what QF sends the carb out with. Does he light insense and perform chants until he passes out before a premonition comes to him.

But seriously I'm curious since I've been asked by others too.

Thanks

[blykins]

Took me 5 minutes to figure out how to get onto Club Cobra. I hardly check on here anymore because it's such a pain to get on from a PC.

So how did you reach out to him? Best way is to call and I would suggest that you try him again if you couldn't get a hold of him. I've never received an email from him and I think he's on Facebook and IG, but I don't see him post much.

When you dropped altitude, you added air, and so you'll have to add fuel to compensate. Any time you have a stumble or hesitation, it's most likely a lean stumble or hesitation. Where that hesitation occurs determines on which circuit you have to modify. Changing jets doesn't always work, because you also have an idle circuit, a power enrichment circuit, and air bleeds that help get the mixture right.

If it's doing it at lower rpms, then it's probably in either the transition from idle circuit to main circuit, or it needs an extra shot of fuel when you're tipping into the gas. If you're getting into boost at that point, then it could be the fuel pump not referencing the boost signal correctly.

Can you give an rpm at which this stumble occurs?

As far as what we do with the carbs (I say 'we' because I take responsibility for what I send out, even if Scott does work for me), it's on an order-to-order basis. A lot of times, we order parts in and custom build the carburetors. Other times, we order from Quick Fuel, get the carbs, completely disassemble them, inspect, sonic clean everything, then reassemble with the correct calibration for the engine that it's going on. Most of the issues that we've seen come from QFT involve debris in the carb, boosters that weren't drilled, etc.

Scott will often hand write the parts used if they don't jive with what QFT sent with the carb. If the parts jive, then it's just easier to throw the same card in.

As far as your carburetor being rich to begin with, it was intentional. Anytime boost is involved, it's better to be rich than lean. The amount of boost is often a variable instead of defined and we never know the state of condition that the engine is in. Also, if an engine is worn out, then it won't pull on the carburetor as hard, which means that we need to push more fuel through. Engines that are new and are sealed up well will normally need fuel pulled out because they pull harder on the carburetor.

Again, I would suggest giving Scott a call tomorrow and he can help you dial it back in for a lower altitude.

[RedHawk]

Okay understood.
Stumbling at lower RPM at say 2000 to 2500 while in 5 and running about 65 to 70 mph and doesn't improve above that. If I am simply cruising no real issue.

I have a new Aeromotive fuel system including regulator AN hoses send and return with fittings and phantom fuel cell. At idle and it hovers around 5.5 then when pulling throttle up to 3000 it climbs to 6.5ish sonit looks like fuel pressure is adjusting but I don't have gauge inside the car so don't know for sure.
Should I check vacuum pressure to inspect whether PV is correct. I ask because I don't want to start changing a
Umch of stuff that Scott may have done. Early on Scott did say to adjust idle screws which I did and that helped in Co but haven't messed with that.
Is there a heirchy checklist to go through when messing with tuning.
Like check plugs then vacuum pressure change jets and inspect plugs then to something else and so on?
Thanks Brent for the quick reply and lol I just posted this so my timing was great.

I will call Scott too. Fyi I sent him a text a week or so ago.
Scotty

[vector1]

IMO that stumble is the transition from idle circuit to main circuit. Most everybody has forgot how to set up a carb. I did some research on the carbs for the Boss 302 and the holley carbs of the early 70's late 60's along with whatever else info was available.

I have an a/f gauge on the JBL so I could watch what was going on. I came to accept the wild swings of the needle as normal for a carb but wasn't really satisfied, tried quite a few setups and have all the tools and parts to make the adjustments.

After doing the research above, went out to the shop and found a Holley 750 with center hung floats no less that came off a Ford 400M.

Here is that setup on the 400M, and this was in a truck btw, so it should be useable in a lightweight cobra imo. I use it on a 408 and a 351 with small adjustment to the main jets. The a/f gauge needle is so smooth it is unbelievable.

Primary main jet 73
Secondary main jet 80
IFR .029
IAB .070
HSAB .029
PVCR .052
PV 6.5

No siphon breaks on the primary block, .026 siphon breaks on the secondary block

5 hole main well top to bottom--.026 BL .026 BL BL (two hole main well would be both .026)

With this setup in a Holley 750 HP except 74 main jets all around on the 408 netted cruising a/f of 13.5-14, little rich. On accel it would richen to 12.5-13, very smooth and no jumps.

I would try the exact same thing on your 351 with blower, which is probably close to the 400. Should light up your cockles.........

hth

ps, this setup pulls all the way from idle with no problem, note the .029 HSAB and main well settings are important.

[RedHawk]

Originally Posted by vector1

IMO that stumble is the transition from idle circuit to main circuit. Most everybody has forgot how to set up a carb. I did some research on the carbs for the Boss 302 and the holley carbs of the early 70's late 60's along with whatever else info was available.

I have an a/f gauge on the JBL so I could watch what was going on. I came to accept the wild swings of the needle as normal for a carb but wasn't really satisfied, tried quite a few setups and have all the tools and parts to make the adjustments.

After doing the research above, went out to the shop and found a Holley 750 with center hung floats no less that came off a Ford 400M.

Here is that setup on the 400M, and this was in a truck btw, so it should be useable in a lightweight cobra imo. I use it on a 408 and a 351 with small adjustment to the main jets. The a/f gauge needle is so smooth it is unbelievable.

Primary main jet 73
Secondary main jet 80
IFR .029
IAB .070
HSAB .029
PVCR .052
PV 6.5

No siphon breaks on the primary block, .026 siphon breaks on the secondary block

5 hole main well top to bottom--.026 BL .026 BL BL (two hole main well would be both .026)

With this setup in a Holley 750 HP except 74 main jets all around on the 408 netted cruising a/f of 13.5-14, little rich. On accel it would richen to 12.5-13, very smooth and no jumps.

I would try the exact same thing on your 351 with blower, which is probably close to the 400. Should light up your cockles.........

hth

ps, this setup pulls all the way from idle with no problem, note the .029 HSAB and main well settings are important.

Thanks!
See I thought the stumble precipitated jetting up on the secondary to 86 so your saying down to like 80. I'm in Dallas.
I hope you don't mind but I attached pictures of plugs 4-8. From my research it looks the burn marks are closer to the threads meaning too much timing. Also I am reading that more than 3 rings showing a glaze from the top also indicates too much timing. Thoughts?

[RedHawk]

The first pic is plugs 4 and 5. These are 7&8

[vector1]

To me the plugs just indicate you are not burning oil. You could be cruising lean, accelerating lean, lean at idle.... you don't really know. I'd guess from your carb card you are pig rich anywhere the lean spot is not between your idle and main circuit, hence the clean porcelain and tip and carboned threads. Without the a/f gauge your guess is good as mine.

tried to edit my above post--if it wasn't evident, the secondary PV on the OEM Holley that came off the 400M was plugged. I used 74 main jets all around on the HP 750. You can do either. I'd also prefer the single plenum intake over the dual.

Also just an fyi, the Holley Boss 302 carb main jets were usually down around 70, and maybe they used a 780 cfm.

[blykins]

Did you talk to Scott?

The plugs are showing it's lean. The porcelain looks extremely white and bright.

The ground strap is what indicates if the timing is close or not. By the looks of plug #5, timing is pretty close to where it needs to be.

To me, it looks like the idle is a hair rich and then everything after that is lean.

I think the plug may be a little too hot as well.

Next time you throw plugs in it, just use a drop of oil on the threads. The copper/nickel seize makes it very hard to read the plugs. That stuff gets everywhere....

[jhv48]

I’ve run both of those vacuum secondary carbs on two of my engines and wasn’t pleased with either one of them. Vacuum secondary carbs are designed for cars that are much heavier than ours.
You are running lean. The plugs tell the tale.
You’ll be happy with either the Holley or QFT double pumper. Right out of the box they’ll be a bit rich, due to your altitude. Easy job to drop down a couple of jet sizes on both primary and secondary sides till the plugs look right.
Order either one and don’t look back. You’ll love the difference moving from vacuum to mechanical secondaries makes.

[Texasdoc]

Just a word of caution. I bought a carb from blykins that Scott built. It barely ran it was so rich. I called him multiple times and finally spoke to him. He just blew me off saying he builds lots of carbs and didn't remember building mine. It was way off. Ran 10:1 at cruise on the transition circuit and richer at WOT. I ended up having to redo all the circuits, including the Air bleeds, jets, accelerator cam, and install transfer slot restrictors. I finally got it running well, now it is almost perfect.

I don't feel blykins is responsible for this one. He offered to take it back, test it, and fix it. I think he ordered it right but Scott didn't build it to blykin's specs. I didn't send it back but learned how to adjust it myself. Now it runs great and I know how to adjust it if needed.

Not trying to run you off or take business away from blykins. He stands behind everything he does and will make it right if there is a problem. Just know not everything is 100% all the time. Don't believe in the "bolt it on and go" mantra. With these cars, there's always something.

[patrickt]

Originally Posted by Texasdoc

J I didn't send it back but learned how to adjust it myself. Now it runs great and I know how to adjust it if needed.

I don't know why more people on here don't do that. C'mon, a carb is nothing more than a glorified straw with a bunch of holes in it. It's just not that hard to get them right when you have the luxury of tweaking, driving, re-tweaking, re-driving, time and time again until you get it just right. Expecting somebody to build you a carb, when they don't have your engine and car there in front of them, is like having a suit tailored by somebody who's never laid eyes on you, much less put a tape measure on you....

[blykins]

I am responsible. Anything that leaves my shop that I build or someone else builds for me, I'm responsible for it.

I can't remember your situation, Tom....I found a couple of emails from 2016, but I can't remember the specifics.

I will say that even if the carburetors are built to someone else's specs, they shouldn't be 10:1 at cruise. I know we had a rash of blown power valves for a bit, maybe that was the case in your situation. But even if a jet is off by 3-4 numbers, it's not going to be that rich. Same thing with air bleeds. There has to be a pretty significant issue somewhere to make something have a 10:1 A/F ratio.

These things are machines, with parts that are made on assembly lines. There's a bell curve to everything and ever so often we get a piece that's on the outside of the curve. Stuff happens.

I couldn't begin to count how many carburetors I've sent out and can count issues that we've had on probably 3-4 fingers.

In Redhawk's case, he's dropped a few thousand feet in elevation, so it just needs retuned. Blow-through carbs generally need to be tuned on a chassis dyno anyway, but we will do what we can to get him close.

In your case, I would have appreciated it if you would have let me actually get the carb back here and go through it again before you issue out a caution to everyone. I can't make things right if never given a chance.

[RedHawk]

Okay just got off the phone with Scott the one who set up the carb for Brant.

Anyway we went over a few things.

First, Scott mentioned, as I suspected to take somewhere around 3 degrees of the timing out based on where the burn marks are on the ground strap. This by itself could cause the lean conditions and just by backing out the timing it could richen it up a bit. I am vacillating on whether to do this first
Solution; Back out timing to 33 or 34

Also since I came from 5000' in Denver still with Dallas heat and humidity adjustments could be as if I was at an altitude of 3000 to 3500' so jets May not be the issue.

Scott also said and as I have read that I need to look for any vacuum leaks which I will do. It is my understanding that this should justify the PV as mentioned below assuming that the reading is the 13 range.

Scott also mentioned to install an O2 sensor in order to determine A/F mixture, but then I'm jacking up the car and welding a bung on the exhaust bla bla bla. I have a lincoln mig welder but honestly I just moved and most of my tools are still packed and my garage setup is still somewhat disheveled. I asked if he knew of any other product out there where I didn't have to go to those lengths. He said he thinks Holey has a clamp on solution. I will look as Scott said he would explore that too.

What Blykins suggested was the plugs may be a little too hot and that makes some sense in that I dropped to a colder plug but I re-gaped them to .028 to increase the heat per the recommendations of the Supercharger Torqstorm but this re-gap may not have been necessary since I went with a colder plug.
Solution: Get new plugs and Re-gap to at least .030

I also asked if the PV now at 4.5 was correct as my research was showing justifications for 6.5. Scott like a Man admitted he missed that since he overlooked that the car was a manual so he said my suggestion was spot on.
Solution: Replace with 6.5

Scott also said to check the High Speed Bleeds since even a small speck of dust can cause havoc on the carb.

I forgot to ask Scott but I ask what the order of adjustments should be so i will list what I think they should be and any other suggestions are truly appreciated.

• If an easy acquisition get an O2 sensor installed and check for readings.

• Check timing

• Check for vacuum reading and determine if any leaks/fix

• If Vacuum reading shows justification for PV at 6.5 do so now. Half of reading determines PV

• While carb is open check High Speed Bleeds for any blockage.

• Get a new set of plugs probably one set at colder spec and another at the original spec I had in the car and keep gap at .030 instead of .028 I have now. Going to start with colder plug first.

• Test car and read plugs.

• For silky and shinny hair Rinse and repeat.

Upward and onward.

I will report back my progress and and results.
Thanks everyone for your help.

[patrickt]

Originally Posted by RedHawk

For silky and shinny hair Rinse and repeat...

Uhhhh, around here you're preaching more to the Rogaine crowd....

[fastd]

no disrepect to carbs, but Holley Sniper