If you look at the air horn on the carburetor you'll find the Holley list number.

Here's a typical picture

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Sometimes it says list in front of the number, sometimes it doesn't. This one is a Holley 4160 and the list number (50419-1) identifies it as one of the bazillion or so different versions of a 4160 that Holley built.

Yours is probably a Holley 4160, but you can look up the list number or post it here and somebody will tell you what it is.

Not knowing any of the background/history of the carburetor, you may have junk between the needle and seat causing the overflowing and float adjustments won't help that, but a good cleaning and or new needle and seat assemblies might.

So.............more info needed 

Still had difficulty starting after nearly getting swamped by a surf boat. Could use advice on how to move forward. Part numbers for the needles, etc.

Thanks….

DH

Thanks again

DH

The early ones like yours had externally adjustable floats and had no J tubes on the bowl vents, just straight tubes sticking up like in your picture.

The J tubes came along in the later 70's and can be retrofitted. They make sure any overflow out the tubes goes down the carburetor throats into the engine and doesn't spill outward onto the manifold where it can cause fires, explosions etc.

You want to find one that deals with externally adjustable floats like you have and not the internally adjustable ones.

Things like the needle and seat assemblies and the floats themselves don't interchange between the 2 different styles

Almost forgot, you wanted advice................stay away from thirf boats  and the rest of the advice would be to go through the whole carburetor with the renew kit.

I am seeing zero markings on these. Do we have a part # suggestion for replacing?

Holley part number is 6-506, about 20 bucks each.................or the renew kit mentioned above with all kinds of other parts needed for 60 bucks.

Or you can cross reference those numbers to other companies needle and seats or rebuild/renew kits at a variety of prices 

So..............what's this engine and what's it in 

You will have no trouble.  I rebuilt mine with no carb rebuilding experience.  If you have experience it should be no problem.

Looks like it is an automotive carb so guessing the rebuild kit is the way to go if I decide to do some investigating.

DH

Pn 34-7

That number comes from Holley's listing of what fits a 6407 carburetor

Now whether yours is all original that might be a different question.

And your carburetor is a Marine certified Holley that started life as an automotive carburetor with a few changes to meet USCG regulations.

I don't usually yell but in this case...............BUY THE RENEW KIT 

That way you can get into the carburetor without worrying about ripping gaskets that like to rip when you take things apart, you'll have everything you need

 Mine uses the set screw to adjust the needle and other uses the nut. Different mechanism doing the same thing. Adjusting pressure to bowl.

Thanks……

PS check your PM inbox

Here are the parts associated with the externally adjustable needle and seat, and they're all in the 703-1 kit

Put the old style seats in and immediately felt closer to normal but the flooded engine stopped the testing for the day.

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One way to make it run really rich is to use the wrong primary metering  block gasket. Holley gives you 2 similar but different gaskets in the kit for different applications.

They look like the picture below

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Your carburetor has a metering block that uses the gasket on the bottom with the small hole above the cutout for the power valve

If you used the one on the top, you'll have a really rich running engine.

So, check your leftover parts collection to see which one went into the carburetor  

It's a safety thing. It has nothing to do with your current problem, but if the diaphragm ruptures it'll be spraying gas around in the bilge near hot exhaust manifolds and things that spark

He was nice enough to put a marine Mallory distributor on it for you though, so thank him for that.

Kit came with a 2.5 and 7.5.

Should I swap it for one of those as a start? Will test with vacuum but wanted to check for best starting point while it’s on the bench.

DH

Since you don't have an 8.5, I'd probably put in the new 7.5  since it's new and shouldn't have any leakage issues of it's own and give things a whirl with the swapped gasket and new power valve

Holley renew kits are kinda all over the place with their power valves for whatever reason.

Safe to assume that you blew out every passage you could find with cleaner and compressed air?