750 DP alky settings

[Krooser]

Just spoke with the original owner if this carb...bought it direct from BG himself. Said BG set it up for him and nothing was ever changed except bowl gaskets 10 years ago.

So....

[barnym17]

Krooser I really believe the boosters will give you trouble my 800 holley on e85 is using .180 down legs and is working very well, you are going to need much more fuel with methanol than I do with e85.In the old days when not changing boosters a lot of crutches were used to get a fairly usable fuel curve. Such as higher fuel pressure and float levels, these were only partially effective.You can open the booster yourself I took mine out opend to .180 with a drill bit by hand then reinstalled using red Loctite, then epoxied the boosters to the main body also safety wired them for insurance.
This will make tuning much easier on you.Also the cross channels can be done the same way by removing the plugs in the top of the metering block plugs are available from jegs for cheap.

[Krooser]

First if all thanks to everyone who has chimed in on this deal. While I have tuned dozens of Holley carbs over the years I've never had to mess with boosters or enlarging the innards...

I can imagine how many crutches were used before good aftermarket parts became available.

I'm going to try to visit my carb expert tonight. He runs the desk at a machine shop during the day and does his carb work at night. He can pull the boosters for me and reinstall them when I'm ready.

I think I'll do what I can to make this carb right but try to find the cash to get a modern purpose built alky carb. I want to dyno this engine and I can use the two carbs for and a/b test.

Again thanks to all.....

[pamotorman]

this is the type of drill you need so it drills straight. https://www.amazon.com/gp/product/B002P ... =256258011

[Krooser]

this is the type of drill you need so it drills straight. https://www.amazon.com/gp/product/B002P ... =256258011

Alvord Polk? That was the British guy that lived down the street from me when I was a kid!

BTW PA... never ever saw a drill bit like that... I was going to use an old brace! Thanks for the tip I needed that.

[pamotorman]

it is a counter bore and ones with a interchangeable pilots are better because you can make the pilot any diameter you need.

[Krooser]

it is a counter bore and ones with a interchangeable pilots are better because you can make the pilot any diameter you need.

Where do you find them? MSC, Grainger?

[pamotorman]

it is a counter bore and ones with a interchangeable pilots are better because you can make the pilot any diameter you need.

Where do you find them? MSC, Grainger?

any machine shop supply place should have them or can get them.

[Krooser]

Are you actually sure this is an alcohol carb? The easiest way to tell is to measure the feed holes in the boosters, and the angled passages near the top of the metering blocks that feed the boosters. For Methanol. the booster passages should be at least .180", and the metering block passages even larger. The 4779 gas carb came with the booster passages at.160", and the metering block passages at .140".

The needles and seats you use will need to be much larger that .110". The actual size will depend on what your fuel pump is.

What type of fuel pump are you going to use?

I'm using methanol. I pulled one plug out of the top of the metering block... it's opened up to .225. I'll get all of them out and clean the whole shebang but it does look pretty clean in there. I'll open up those angled passes, too.

Still waiting on my rebuild kit.

[Krooser]

QF just let me know my carb kit has been shipped... Nine days after I ordered it. Funny how we have become so impatient in this world of Amazon Prime and near instant deliveries.

[Krooser]

When you are talking about opening up the boosters do you mean the metering block side of the booster where it's s wedged into the main body? If so mine measure about .182 right now. The passage in the Venturi side is pretty large, too. Don't have a way to measure those right now.

It appears the main body bores have been polished in the past... maybe even the booster itself.

[barnym17]

I took mine out and opened both ends of the down leg, went in as far as possible from metering block side , then with booster in a vice went in from the other end and intersected the passage. If your booster measures .182 you may be good.

[Krooser]

What about drilling those two small holes (.080) in the primary throttle plates? I've had carbs with this modification before... better idle speed adjustability? If I'm correct it allows you to open the throttle plates a bit to expose the t-slots at idle.

I was looking thru some Holley info on their newer style carbs and they have changed their design slightly so this isn't needed anymore.

[pamotorman]

What about drilling those two small holes (.080) in the primary throttle plates? I've had carbs with this modification before... better idle speed adjustability? If I'm correct it allows you to open the throttle plates a bit to expose the t-slots at idle.

I was looking thru some Holley info on their newer style carbs and they have changed their design slightly so this isn't needed anymore.

one reason holley bought out barry grant to get the adjustable air bleed patent

[Ks Fats]

I may be out in left field but I try to work on the idle circuit so that I've only got a small square of the t slot exposed usually .020-.025 on the primary. Put a idle speed adjustment on the secondary side to set the idle speed. Usually weld up the holes in stock holley butterflies because they aren't as effective where they are. Drill the holes if needed directly over the idle discharge port in the primaries (.083 for starters); the velocity of the air through the holes helps the atomization and vaporization for the fuel delivered through the idle circuit. Might not need holes in the secondaries at all. I think this all helps the throttle response.