Sooo.....as per my buddy's engine builder he purchased a brand new 650 cfm Holley Ultra HP carb this summer. It went on a 516 cu/in BBC with an M3 procharger. It was dyno tuned and everyone was very pleased. It actually made 888hp @ 6000 rpm and 848 ft/lb of torque at 5000 rpm. That was with timing set conservatively.

The boat was running great, testing props and such. Still needs dialed in but is already 15 mph faster than last year. Last time out we started smelling fuel. While at idle fuel is dripping out of the throttle shafts and it turns into a pretty good leak under load. Holley says the only way this happens is if the bowls are flooded but they have sight glasses on them and the fuel level is right where it is supposed to be.

Anyone else have any ideas? Can the boost be forcing it's way into the bowl somehow and be pushing fuel out?

First thing that jumps out at me is only a 650. I would think that would be on the small size.

Now as far as the leak issue goes how is the ducting from the procharger attached to the carb? Is the carb in a box like most applications where the boost will be equal all around the carb or is it attached in a way that the pressure from the procharger only goes into the venturi area?

If

you need to call pro systems,they make a plate that goes under the carb to correct that problem.been there done that.

Blow thru carbs tend to do that unless in a box. There was a method of sealing the shaft but I can't remember it right now.

Pressure drop across a blow thru carb is much different then when they measure cfm rating at the manufacturer.

Yes the same engine needed a 950 with a roots style blower and it made less power.

It has a carb hat from procharger on it. No box.

Years ago I had a blow through sbc in a car and had to have the carb built for it, special floats, and sealed shafts and a special power valve. Before that it leaked and crushed the floats.

This was part of the reason that the Ultra HP was purchased. It already had the right floats and PV per the engine builder, Holley tech support said they had no way to better seal the throttle shafts. The carb does not have J tubes on it, do you think this is allowing boost to blow into the bowls?

boost IS getting in the bowls,that is why you need the floats that will not colapse under pressure.j tubes will change nothing,the pressure gets in through the vents no matter what style they are.