Seeking Carburator Recommendations

I put a Holley 750 with vacuum secondaries on my car and it work fine ... of coarse you still need to adjust the carb and sometimes if the camshaft doesn't produce enough vacuum you might have to change the power valve ... and maybe the primary jets ... but that can be changed very easily.

It sounds like you have a blown powervalve. If it's leaking it will be VERY rich at idle. Also check your float level. I just went thru this with my 650 DP.
I eventually ended up replacing the powervalve (Part Number: HLY-125-65)


A quick way to check for a bad powervalve is to get your car up to operating temperature and then turn your idle mixture screws all the way in. It should die out. If it doesn't then you have a bad power valve.

I also replaced both Needle and seat assemblies (Part Number: HLY-6-504) as the O-rings for both were leaking and allowing the fuel bowls to overfill causing it to run rich as well. The needle and seat themselves were fine, the o-ring that seals the assembly had shrunken over time.

Alot of good answers ! I'll check if my Powervalve is bad, for sure. Would be an easy (and cheap) fix.
But still it sounds like a 750DP carb is too much for my engine. Just as I thought..... But it was on the engine when I bought the car.

Andy is right - an interesting topic with many different opinions...

I am running a Holley 735 CFM (4150 series) with vacuum secondaries. It run well on my mostly stock engine.


So I would suspect a 750 CFM properly tuned could be made to work.

Regards -

Rocky

The topic of carburetor size is covered in sticky #3. A 750 cfm carb is not too big for a 351C 4V if it is jetted properly. The 4300D factory carburetor is 750 cfm.

In regards to jetting, Holley double pumpers are usually jetted "fuel rich" out of the box, because they are jetted for a motor with low intake manifold vacuum. If you install them on a motor with high intake manifold vacuum, they will be too rich at idle & low rpm. Its best to select a carburetor with leaner jetting, which is normally referred to as street jetting. Sticky #3 also has some carburetor recommendations.

There is always the option of having a "tuner" re-calibrate the carburetor for your motor.

-G

There are a lot of great carburetors out there for your application. Agree that 600-700cfm is the right range. You may want to check out the new Street Demon in a 625 or 750 cfm. It is a brand new design that took some of the best features of a Holley and a Carter/Edelbrock carb.

Uses Metering rod for the primaries with triple stack small boosters for great low rpm streetability and response, but then employs huge mechanical secondaries with a flapper valve to dampen the operation so a second accelerator pump is not needed. Very tunable both from a metering rod/spring standpoint and holley secondary jets with an adjustment of the flapper valve to determine when they kick in. It is jetted correctly for a street motor out of the box. I only had to adjust mine for altitude.

It has polymer one piece fuel bowl to insulate it from heat and it will never leak. I have run a lot of different carbs over the years, including the Summit carb which worked well also, but this is my all time favorite right now.

Let me put in a plug for the technology I am using - the FAST EZ-EFI throttle body fuel injection. It bolts to the standard Holly square bore bolt pattern on the manifold, flows 1000 cfm, and solves most of the compromises that have to be considered between performance, throttle response, and streetability. Not to mention that tuning can be done with the push of a few buttons on the hand held pendant.

Yea, it is 4x the cost of a carb, doesn't work as well with big, lumpy cams, and it somewhat technical to install, but when you get it right, it is fantastic to have instant throttle response and better fuel mileage.

As was mentioned, if you want high speed performance, use a 750-any-type. If you want moderate performance with good driveability around town, use a 600. A 750 will add roughly 30 bhp and drop 4 miles per gallon with no other changes, even if you drive the car the same with both carbs.
Some guys try even larger carbs (usually with drag racing backgrounds). One Pantera owner went from a 750 DP to a 950 Dominator. He reported the engine made much more noise, less power and gave 9 MPG. Want to buy a cheap, lightly used Holley Dom?
Note that ANY DP carb new-in-the box will be jetted quite rich. Holley expects owners of these race-type carbs to tune them for specific uses and they know one cannot easily blow up an engine running rich. So warranty returns to Holley are far less this way; but they simply don't work at optimum without extensive fiddling.
Some of us use 'tuner-carbs' which are 650 or 700 DPs that have had 35 or more major changes done to them specifically for street driven Panteras. Pro tuner shops that sell these usually dyno each carb on the same type of engine they will be used with before shipping them. Cost= about $750 USD. Mine actually gave a small power increase over a 750 vac-sec, was more responsive at low speeds and gave 20 mpg @ 90-110 mph continuous touring speeds, over several 800-mile runs. It was a bolt-on with no fiddling needed. Now 10 yrs old & still working fine.
I recommend tuner-Holley carbs- they do everything throttle-body injections do except barometric compensation & a slight mileage gain, at 1/3 the price. I won't live long enough to see any fuel savings from a $2000+ TBI setup, at 20K miles per year. FWIW-

Wow - Alot of good replies. I'm planning on digging out the car today (Restoring my house) and figure out if that Powervalve is bad. And then I'll figure out what to do.

Did you ever get your Carb sorted?

Oh, Yes..... Forgot 'bout that. I'm rebuilding my house at the moment, so not much time to be in front of the PC.

But it was the powervalve. So bought a rebuildkit for the Holley carb, and now it runs much better. Still a bit to rich, but better !

Good.

Now check your float needle valves (see my earlier post). The "O"-rings shrink over time and allow the float bowl to overfill causing a rich condition as well.

My motor is basically stock with a performer manifold and I have had the Carter AFB carb for over 20 years. It is the same as the Edelbrock one and it does not have a power valve. I think it is the 625cfm model with vacuum secondaries. I had bought the jet kit and dialed it in myself. It is also easy to rebuild if needed. I have found it to be a good trouble free carb for a stock application.

QUICK FUEL TECHNOLOGY 750 WITH ANNULAR BOOSTERS MECHANICAL SECONDARIES

When looking for another Holley, think this way. Look for a Holley that was built for a production car that has similar characteristics to yours.

The 3310 comes to mind. Versions of that carb were on the stock Boss 302 and the Z28 Camaro.

Out of the box it will have a much cleaner idle than a 4779, which is a 750dp Holley carb.

That carb is heavier at idle than the Webers are and will smart your eyes.

The issue with it is that it is actually the idle air bleeds that are too small and need to be enlarged to lean out the idle.

That's best left to an expert but you can save a lot of time by going to the 3310.

Expect about 12mpg though with it.

Best out of the box street cruising carb would be a plain ole' 1850. Bolt it on and go.

It's good for 6,000 rpm plus on a stock Cleveland.

Most people put way too big of a carb on to begin with. Sometimes even the factory.

quote:

Originally posted by 1973 Pantera:
Good.

Now check your float needle valves (see my earlier post). The "O"-rings shrink over time and allow the float bowl to overfill causing a rich condition as well.

I will. But reading PanteraDougs post, I really think about just ordering a new 3310 Holley for it and place the old one on the shelf.

I used the Ford over the counter carbs back in the 1970s (and 1980s when I could find them) and believe me, the list 3310 is not in their league. I wouldn't let a friend buy one. The Holley list 3310 is notoriously poorly jetted out of the box, and has been that was for 4 decades. Doug hinted at that. It can be tuned to operate well by somebody with the skills to tune it, but don't expect to bolt it on your motor and be done. It is a 4160 style carb lacking the provision for replaceable jets on the secondaries, has a manual choke, non-adjustable air bleeds, etc.

Now, if you want a 750/780 cfm vacuum secondary carb investigate these 3:

The Demon Carburetors #1402020VE 750 cfm vacuum secondary Speed Demon. It is street tuned out of the box, it has annular boosters, electric choke, replaceable air bleeds, etc. That is a good carburetor.

Quick Fuel Technology #SS-780-VS is a 780 cfm SS Series (street) vac. secondary carb with electric choke; it is very similar to the 750 Speed Demon, lacking only the annular boosters. The Quick Fuel carb is much closer to what the Ford factory Holley carbs were like.

Finally, for the most bang for your buck the Summit Racing #M08750VS 750 cfm vac. secondary carb with electric choke is a low buck bargain that even has annular boosters, it will walk all over the 3310 out of the box.

-G

3310 has become a generic carb. That is actually the original Chevy number from the Z28. It's a 780cfm.

Ideally, what you want really is a Boss 302 carb and add an automatic choke OR A 428 CJ CARB. They are both generically the same carbs. Maybe all three are just a little too big for their original factory applications?

The Boss 302 is rated at 780 and the 428 at 735. They are very similar carbs. Both would be bolt ons for the Cleveland (the boss 302 is manual choke though) with a square bore intake and could be run as is if you aren't picky.

I ran that carb on the C (B2). It ran great, fantastic in fact, out of the box but it's now a pretty expensive carb because of what it is for.

You can get very close "continuation build" Holley carbs from Carls Ford Parts. They are not cheap but work well. The difference between the B2 carbs is one has 78 secondaries and one has 82's. You have to ask Carl, which is which.

I think the 428cj carb has 70 mains and 72 secondaries. That would work for you out of the box.

The Cleveland likes the B2 carbs because essentially it is a B2 with more cubic inches, but remember those are manual chokes. You would need to put the Holley electric choke kit on it as well.



Personally, I'm not afraid of the secondary metering plates instead of jets. That's not a big deal at all. You don't need secondary jets. The metering plates are fine. The reality is that 95% of any carb tuning is done in the primaries. The secondaries are going to stay put and you only need secondary jet changing ease if you are doing a lot of changes.

Probably any of these carbs is going to run 67 main jets, 6.5 power valve. The equivalent of 72 secondary jets. The Boss and Z28 both ORIGINALLY had 78 secondaries. Why? Beats me. Those are too heavy even with headers and open exhausts under race conditions.

For a stock 351-cj, low compression, even 70/72 is heavy.

ANNULAR venturis ARE VERY HIGHLY DESIRABLE on a carb.

When I first got my Pantera it was running an Edelbrock intake and the generic, out of the box 3310. Secondary metering plate and all. It ran fine. It just wasn't a race car.



Carbs are like camshafts. People TEND to over do it.

The Boss 302 carb, is actually way to big for that engine. So is the 3310 for the 302 Z28 and as a matter of fact so is the Holley 3259 that Shelby put on the GT350's, a 715cfm originally on the 427 Cobras. Both the B2 and the 289 Shelby, should have had 600 cfm Holleys on them.

I just saw dyno results on a 67 289 HP with 2x4 Holleys and a 68 302 with the 600 cfm S8MS Shelby Holley.

The 289, for a T/A racer with real GT40 heads, made 375hp and the 302 365hp. That is a nice strong number for the 302. That 600cfm Shelby carb runs very well. It doesn't kill torque like a too big carb would.



I ran a 4779, 750 dp on the Cleveland for a long time. I had the primary air bleeds leaned down to stock 600 cfm sizes, so the idle wouldn't smart your eyes. It liked 70 main jets and 72 secondaries as the final set up.

On that carb, as on most Holleys, leaning the idle mixture that means enlarging the diameter of the idle air bleed very accurately with a pin vise and numbered drill bits. This is like setting the a/f ratio on Webers with both changeable air correctors and main fuel jets but once the air bleeds are too big, you are screwed, you can't go back.
Better know EXACTLY what you are doing.

Leaning out the idle screws on a Holley only changes the volume of fuel at idle, not the a/f ratio which is built in.

The 750dp ran to 7500rpm AND even with that set up, plugs were still showing heavy with those jets.



I think that a 600cfm carb will crispen up the throttle on a sluggish low compression 351cj. Been there. Done that. I think a 750 is too big for that engine with the 8 to 1 compression ratio.

The 1850 is lean out of the box but will make as much power as the 750 does when you jet it up. Particularly the secondaries.

It will give you 4 or 5 mpg better mileage and pulls very, very hard in the lower gears at WOT.

It will also have a better idle than the larger carbs do because of a stronger signal to it.



I went with 2 4180 Holleys on my 2x4 set up. 59 main jets and 119 secondary plates. Those are annular discharge venturis and the difference between them sensitivity wise and the 1850 is night and day, AND the 1850 is very good. Annular discharge is just so much better! The carbs also are 4 corner idles which helps a lot also. That's a very tricked out set up.



None of these carbs are perfectly set up for you out of the box. The 1850 will likely come with 62 or 63 mains. That's going to be too lean and would need to be changed. The other carbs probably will like 70 primaries, but come with 67 primaries.

Therefore how they come out of the box doesn't matter all that much. To get them right and pull hard, you need to do a little work with them. Probably just a weekend, uninterrupted, as long as they aren't too big for what you have.



I am not aware of any carb, other than the two Ford carbs and possibly the ORIGINAL 3310, that would be jetted really close to what you need right out of the box.