at this point I would call Tom at weiand, he is the blower guy there and is very sharp, has helped me a lot ! Rob

Idle mixture is controlled by the air bleed screws on the side of the float bowls. Check your primary jets by running just below the point where the secondaries start to open, typically about 3800 rpm. I bet they won't be black there. You've already checked wot and that's lean. If you have 6 lbs. of fuel pressure at the carbs and your ignition is functioning properly, start jetting up.

Does it pop through the carbs when you hit the throttle from 3500 RPM to go to WOT or are you already at WOT when it starts to pop through the carbs?

How much higher have you gone on the main jets so far?

if your flat tappet still,have you checked the exhaust lobes?

It seems to start popping at about 5000rpm. Motor should spin 5800. If I keep it about 3/4 throttle, it runs faster. As soon as I open it up that last 1/4, it gets to around 5000 and starts popping thru the carb. Right now, I haven't rejetted as of yet. Currently running 74/84 with 6.5 pv on the primary side.

Its sounds to me like you are leaning out in the upper rpms. I would jet it richer in the primaries and secondaries by about 4 sizes and go from there.

You really can't go by the color of the porcelain for plug reading any more. Fuel burns too clean to leave the nice light brown and they are almost always white at WOT. You need to look at the base circle of the plugs.

Agreed 4 sizes would be a good start. I would keep going until there was a little color on the insulater and definate color on the ring. Another thing you can use as an indicator is the oil temp. If the oil heats quickly under boost you may need more jet.

PVCR= power valve channel restriction. These are the holes in the metering blocks that are open to the fuel bowl when the power valve actually opens. They are drilled passages which control the amount of fuel that is bypassed around the main jets under low manifold vacuum [enrichment]=(open power valve). Unscrew the power valve and measure the hole size. From this determine the area of the hole and compare this to the area of the jet. (see Holley jet tables).
The area of the secondary jet should be similar to the area of the primary jet + the area of the PVCR when the primary and secondaries are the same size, like a 750 or an 850 cfm

Also you should check the needle and seat, inlet to the float bowl, size. For your combination, the bigger the better, like .140" or .150".

Check Holley for this information. If this still isn't fixing it, call Dean Nickerson. He does these carb conversions all the time.

Forget about the seats, you have two carburetors= 350 hp each is OK.

Are you running a different cam? Many aftermarket hi-lift cams (eat) valve springs [loose seat pressure], in marine applications!

JB

Some more information on PVCC and 750's.
http://www.hangar18fabrication.com/blowthru.html