You might be running out of fuel in the float bowls. I had the same prolem on a 468 with a 850 vac secondary and had to use a high volume holley pump. I have one that is brand new with -6 fittings for sale that I used for 3 days in blythe. Bought it from a speed shop in blythe for $160 ill sell it for $130

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I dont have a pressure reg or gauge. Im going to buy a gauge tonight and see if the pressure drops off at that speed. Im also going to check the advance weights in the dizzy to see if their stuck. The fuel pump is the stock mechanical one. You think it might not be enough?

Any kind of feedback would be helpful. Any engine I had, no matter car, truck or boat I would not even think of running it without a fuel pressure gauge or a boost gauge. I always had one eye on my boost and fuel when in my boat.  Never had a hint of problems with it either.

Ok, you also want to make sure that you are not vapor locking (fuel press gauge will show this) your system. The cause could be lack of fuel venting. Most of these boats have built in vents in the caps. If they fail to vent the tank it could cause vapor lock. I never trusted this set up so I made my own vent set up. You need to inspect from the pickup tubes in the tanks (make sure they are not clogged, cracked, i.e. sucking air or fell off) all the way to the pump, lines and carb. If you are going to keep the big block happy and want to run a mechanical pump put a Clay Smith pump on it and you should be good to go. Also you want to make sure your fuel line size is adequate. Back when these boats were stock from the factory (mild BBC) the fuel systems were produced to just be able to support the stock BBC. I have seen some fuel hoses that were less than ¼” inside diameter.  My system was completely overkill, ¾” id pickup tubes with -12AN to1200HP  EFI pump to -10AN to -10AN fuel rails. With the line off and the pump on it looked like a garden hose on full blast.

Then again you could be barking up the wrong tree and it possibly could be an ignition or timing issue. However fuel pressure readings and making sure your ignition curve is correct is the place to start.

Ok guys,

I am going to list what ive done so far-- after everything ive done there is still no change at 4,000rpm

What ive changed:

Holley 110 gph fuel pump

Bumped Jets up from 74 to 80s

Rebuilt the carb and also tried another carb that I know works well

Replaced fuel filters

Replaced Cap/Rotor and Condenser and Ignition controle module and coil

Ive checked and cleaned all my grounds, I ran the boat with the tach unplugged and the alternator unplugged, Ive ran the fuel pump off a 5 gallon gas can of fresh 92 octane.

Ive checked for vacuum leaks several times

Ive ran it with the vacuum advanced disconnected

Whether the boat has a load on it or even if I rev it on the trailer it still breaks up around 4,000RPM

     IS there anything you guys think I should checked?? Im seriously out of options at this point. The only thing left that I think it might be is either the mechanical advance weights and springs need to be changed or the distributor has some other type of problem that I dont know about.

ok here are a couple of things you can check, its a little far out there but.....    pull both valve covers and crank the motor over, too make sure your cam is still good. if a lobe has worn off the engine will pop at higher rpms. its rare but it does happen.

Thats exactly what I plan on doing today, Im doing a comp test and im going to watch the rockers to see if one doesnt move as much. At this point im really starting to think it is something internal.

ok sp your running a hei ?   try this check all the grounds, add a couple for an experiment . next look at the hei put the cap rotor alll the way to the weights , see if there rusting???  if so check the bearing in the dist.   you maybe shorting out after the weights open fully.

Ive checked the weights and they are in perfect shape. The bearing seems to be ok too. The only thing i cant think of to do is to try a new dizzy and see what happens.

just for fun whats the oil like?  does it smell like fuel?   that cyl that is 118 whats the plug look like ? does your motor burn oil?

The motor doesnt burn any oil nor does it have any blow-by. It doesnt smell like gas and it looks fairly used but not bad. I'm starting to suspect a burnt valve. Im going to run a leak down test on it tomorrow and I'll let you guys know the results.