Holley Carb Rebuild Questions

[69 Rustang]

I picked up a Holley 750 over the weekend and would like to freshen it up and make some changes to it, but have a few questions. The carb is a 3310-4 that is currently stock and almost new. I intend to get a Proform center section as I live in Southern Cal and can live without the choke for what little this car will get driven.

1) How can I clean it properly without removing the gold finish?
2) Can I add a secondary metering plate to this easily? If so, what do I need to do other than buy the plate?
3) Any other advice, I am nearly a Holley virgin...

Thanks for any/all help!

 

[chepsk8]

What size motor?

A 750 is to big for anything under 400CI, unless you will always spin at high RPM's. I had that carb on my 428 SCJ, and I had to jet it down considerably to get it to run right.

If it's vac secondaries, it's better suited for an automatic, as there will be a slight bog until the secondaries catch up.

 

[65ShelbyClone]

1) How can I clean it properly without removing the gold finish?
2) Can I add a secondary metering plate to this easily? If so, what do I need to do other than buy the plate?
3) Any other advice, I am nearly a Holley virgin...

Thanks for any/all help!

I just rebuilt a 4777(650CFM double pumper) for the first time and cleaning it was harder than the actual rebuild.

1) I used a kerosene-based parts washer solvent I have a surplus of. I soaked the parts in a small bucket as best I could, then used a stainless bristle brush to get the varnish off(VERY old and hard varnish). Since you want to keep the dichromate finish, I would recommend a brush with nylon bristles and a can or two of true carb cleaner.

2) I always deal with pumpers if I can so my knowledge of vacuum secondary carbs is limited. I think to make the secondary plate adjustable, all you need is the adjustable metering block conversion kit from Holley(for 4160 carbs, I think). Probably some jets too.

3) Holleys are made of cheap and very soft cast zinc, so be careful with gasket sealing areas and anywhere a part screws into the metal. Nothing needs to be overtightened.

 

[85MustGT]

What size motor?

A 750 is to big for anything under 400CI, unless you will always spin at high RPM's. I had that carb on my 428 SCJ, and I had to jet it down considerably to get it to run right.

If it's vac secondaries, it's better suited for an automatic, as there will be a slight bog until the secondaries catch up.

A 750 is a really big carb. Here is Holley's link to selecting the right size carb...
http://www.holley.com/data/TechService/Technical/Selecting A Carburetor.pdf

3310 is a vac secondary
http://www.holley.com/data/TechService/Technical/4165-4175 Exploded View.pdf

The metering block gives you a bit more tuning than the plate. You can change the power valve and jets in the block.

 

[iskwezm]

I ran a 750 3310 on my 289,it was fine.if you go by the formula everybody is saying ,you might as well get a 450CFM 2 bbl,because that what it calls for

I also got the 2ndary metering plate conversion and a jet kit.

 

[65ShelbyClone]

A 750 is a really big carb. Here is Holley's link to selecting the right size carb...
http://www.holley.com/data/TechService/Technical/Selecting%20A%20Carburetor.pd

Well heck, according to that, a 650 pumper is about the smallest I would want for my 302.

 

[chepsk8]

I have a 600 D/P on my Cobra with a 5.0 Roller motor. Plenty of carb, plugs read perfect.

 

[85MustGT]

My two cents worth -
About 20 years ago I worked at a automotive warehouse and had the opportunity to try a number or Holley carbs on a Pontiac. Double Pumpers from 850, 800, 750, 700, 650 and 600. I was able to have the car run best, in terms of seat of the pants tests, with the 650 and 700. It was a toss-up. The Pontiac was a 455 bored .30 over so it was 463 CID and would run up to 6 grand. It had a mild cam, 3:55 gears and an automatic transmission.

 

[Max Power]

There is an excellent article by David Vizard in a recent Popular Hot Rodding that debunks a lot of myths about carb sizing. Of course, a lot depends on your motor, but a 750 can work on a 302 just fine if tuned correctly, and of the rest of the system will flow enough, the 750 will add a bit of HP to the top end.

The difficult part is getting a larger carb to atomize fuel properly at lower rpms. The pressure drop from the venturi effect is less because the carb bores are larger. Proper atomization can be achieved by jetting properly and getting boosters that work best for your application.

They dyno tested everything from a 650 to a Holley Dominator on a 440 Mopar, and with annular discharge boosters, they were able to get the same response and horsepower between the 650 and 1050 at 3000 rpm, but the 1050 added about 45hp at 6500 rpm.

If you know how to tune a carb, it's hard to over carb an engine.

Problem with all those charts and recomendations is that most people want to bolt a carb on right out of the box. If you are afraid of tuning, then being conservative is the way to go.

Also, carb cfm flow is measured at 1.5 inches of mercury. An engine doesn't always run at that, it's just a standard of measure. They were able to get a 650 to flow about 750 cfm, and they were able to get an 800 to respond on the low end as well as the 650. Of course, at part throttle, your carb is never flowing at the rating anyway, as carbs are variable flow beasts. It's all in the tuning.

 

[chepsk8]

Max,

That's the point I tried to make before, and why I like the Holleys so much, flexibility.

On every Mustang (and now Cobra) that I have had, I have tuned the carb to get it right. In almost every case dropping Jet sizes, dropping the power valve, different springs in the vac secondaries, and new accel pump cams have helped wake up the motor.

In the Mach (428 SCJ), when I finally got thge combo right on the 750 (3310), which included changing all the above, it finally ran incredibly well. Effortless 13.80's at the strip, 14 mpg if you drove it like grandma, and a perfect grey color at the tips. It takes work and experimentation, but when it's right, it's good!

Currently working on the 600 D/P on the Cobra, lots still to do to find the sweet spot.