Thanks for all the advice, I will be looking for a mechanical gauge tonight.

Hopefully I will have this resolved tomorrow.

Paul

Strip,

This is from their tech sheet

Supply Line noise is caused by varying loads of the
vehicle’s supply voltage. These variances are amplified
through the radio’s 12 volt supply wire and are heard through
the speakers. Supply line noise will be audible on AM and
FM as well as during tapes or CDs. For Supply Line noise,
the MSD Noise Capacitor, PN 8830, will help.
The Noise Capacitor will act like a filter on the heavy
power supply wires of the MSD. The MSD will draw its
power though the filter keeping all of the other accessories
separate which prevents supply line noise. A side benefit
is that the Capacitor will protect the MSD Ignition from
voltage spikes or current surges.
Figure 2 - MSD Noise Filter PN 8830.
Installing the Noise Filter Capacitor

I sent a bad msd box back to them, their tech said that a voltage spike got it. Recommended this part for all ignition boxes especially with multiple batteries.

Hopefully I wont know if it works for years

I pulled the plugs tonight and they looked very clean. I think the motor was running lean.

I have relocated the regulator and the pressure senders as close to the carb as possible.

I also pressure tested the intercooler and it was fine, and installed new plugs

I hope to have it running tomorrow night. I am looking forward to a poker run this weekend.

Back in my drag racing days, every time I had a high RPM misfire or breaking up the cause was ignition.
Could be coil, cap, rotor, maybe even wires. I doubt you're running old fashioned points type ignition, but if you are check those too.

i am putting up with the same thing it happens @4700 rpm and earlier if i hit it.its a sc800.i believe it is my cylinder presure blowing the spark out considering im running a stock merc ignition.i just bought a full msd system for it.and hoping to cure it.even if its not the problem it should be on there anyway.if it dont help i will assume the engine was sneezing under detonation and i will go right to a leak down test.hopping its not the case

I was having the same issues as you this summer. My problem was that the fuel pump diapram was beginning to fall apart and the bits of rubber were then getting caught in the needle and seat and not allowing the carb to supply enough fuel past 3/4 throttle. But it would come back to life when I backed off. It sounds to me that could very well be your problem!

+1 Had this same problem with a friends boat 2 years ago, drove us nuts!

Im having the exact same damn problem with same motor. Have 7 psi pressure but i dont have a blower motor. I was thinking it was the mechanical fuel pump, but i flipped on the electric one while running WOP still broke up then runs again.. You guys thinking some new plugs

Check the needle and seat in both the primary and secondary.

i had the same roblem with mine changed everything ended up being the cam,just a thought.