When i rev it, it revs high and good. But if i rev it and hold it, itll bog down from 4000 to 3000 and run sloppy. My guess is the carb isnt openning the secondary cause its a vaccum advance. I also dont know where to put the vacuum port on the manifold to tune the carb with a gauge. The previous owner had a port already in place on the very top behind the carb. I used that just to see what happened and i got movement close to the green zone but only got the highest reading with the mixture screws turned all the way in. Im stumped

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Have you checked for vacuum leaks


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Yessir but i did learn a few things last night.  But I'd rather get confirmation from you when hooking up the vacuum gauge to tune the carburetor does it hook up to the manifold or to the carburetor

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Mine hooks to the manifold


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Did an experiment today. And noticed during experimenting that whenever i take the plug cover off the vaccum port on the bottom of the carb fuel comes out. That doesnt seem right?

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Did an experiment today. And noticed during experimenting that whenever i take the plug cover off the vaccum port on the bottom of the carb fuel comes out. That doesnt seem right?

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You mean the thing the screwdriver is touching?  That is a manifold vacuum port and fuel should not come out of there under any conditions.

The larger brass plug with the slot is the float bowl fuel level sight plug and should have fuel drip out as posted above.

You mean the thing the screwdriver is touching?  That is a manifold vacuum port and fuel should not come out of there under any conditions.

The larger brass plug with the slot is the float bowl fuel level sight plug and should have fuel drip out as posted above.

Yes the vacuum port. I took the plug off and some not alot but some fuel came out

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No the brass screw above that. That looks live a vacuum rube your touching. Don’t think fuel should come from that


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And yes the vacuum port. When i took the rubber plug off a small amount of fuel came out

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That vacuum port opens into this bathtub shaped cavity in the baseplate.  The round hole between my finger and the screw is the vacuum source for the power valve.  There are channels connecting the vacuum port and the power valve hole to both primary throttle bores. 

It's possible that a blown power valve could leak there.  It could also be a cracked main body or metering block.  Hopefully it is as simple as a gasket failure.

That would be one explanation for why you achieved best idle with the adjusting screws all the way in (out richens the idle).

My guess is that fuel is leaking into that area, where it is remaining in liquid form, after the engine has stopped running.

After it sits for a while, is the primary float bowl empty?

Your boat but new gasket, power valve and base plate inspection cost almost nothing. With that said 750 Holley is a good call.


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That vacuum port opens into this bathtub shaped cavity in the baseplate.  The round hole between my finger and the screw is the vacuum source for the power valve.  There are channels connecting the vacuum port and the power valve hole to both primary throttle bores. 

It's possible that a blown power valve could leak there.  It could also be a cracked main body or metering block.  Hopefully it is as simple as a gasket failure.

That would be one explanation for why you achieved best idle with the adjusting screws all the way in (out richens the idle).

My guess is that fuel is leaking into that area, where it is remaining in liquid form, after the engine has stopped running.

After it sits for a while, is the primary float bowl empty?

Just going to buy a new carb. I rebuilt this one but im over it. 2 years of on snd off messin with it and i still havent seen the river with it. New carb coming but holley has the quick fuel line and the brawler im having trouble choosing .

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Vacuum secondaries are mor fuel efficient. Mine work great. Keep us posted.


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Im desperate. I just want to see the boat on the river.

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