4.3 Low Power, Can't Get to WOT

[safdchief18]

Bought this boat earlier this summer. Has not ran well yet. Continuing to correct issues.
I have a 1989 4.3 with the Thunderbolt IV. Starts and idles great but has no power. I've replaced the water separator, cleaned the carburetor, replaced the plugs, replaced the ignition module because I had no spark advance and double checked firing order is correct. Checked timing at idle in gear, about 650 rpm the timing is at 10 degrees BTDC. I know it should be 8 degrees, haven't adjusted that yet. Rev engine up to 2500 rpm and the timing advances as it should now after module replacement.
Took the boat for a test run today, and get's up on plane now, but very slowly. I have to advance the throttle slowly or it will bog and pop. I can get to about 3000 to 3500 rpm but when trying to go any faster I get the symptoms you hear in the video at the link below. If I go to WOT I continue to lose speed. Get back to about 3500 rpm and she cruises smooth as can be with no issues. Just can't go faster.
I'm not sure what to check next.
Please help!

Video link here:

 

[bondo]

cleaned the carburetor

Ayuh,..... Rebuild it,.....

 

[makomark]

2X that.

I'd also change the anti-syphon valve....especially given the age.

 

[safdchief18]

2X that.

I'd also change the anti-syphon valve....especially given the age.

No anti-syphon valve, just a barb fitting at the tank. I will remove carb and rebuild again.

 

[louc]

There is a pick up tube that runs close to the bottom of the gas tank, these can clog & restrict fuel flow.
You can also try running it on a separate outboard fuel tank to rule out problems with the main fuel tank….

 

[Dieter]

No anti-syphon valve, just a barb fitting at the tank. I will remove carb and rebuild again.

Sometimes the antisiphon is in the barbed fitting

2 x rebuild the carb. When u say you cleaned it what did that entail?

Use an ultrasonic cleaner from HF to soak the disassembled carb body & pieces in

Is it a 2 or 4 bbl