Challenger wont plane out?

[moto17]

Help! I just put a SBT motor in my boat, new carbs as well and new fuel lines and on/ reserve switch , (super bn same as stock) after learning how to do the timing I installed the motor.
I lake tested it starts great!. But it will run up to 6000 ,6500 and will only do this for a second or two.... then it falls to 4000 or 4500.

The Raves are brand new and the boat was planing out before with the other motor and carbs ( I swapped the carbs due to they were flooding the motor after it was turned off hot) That problem is fixed now.

I found that the other motor only had a bent rave( a carb bolt tried to go into the motor) so I fixed it and now have an extra.I had allways wanted an extra and it was cheap( I used a core from another challenger I bought for extra parts.I hope to
I have a WSM dealership so the new carbs were not to bad on the wallet and I like to have a extra set to rebuild.

At max throttle it will only pull 4500 and it burbles some like it wants to pull harder then just stays at 4500.
Any input would be great! thank you! (the boat is a 97 challenger with a single 787)

 

[Dr Honda]

OK... it's getting to 6k... and then drops back. When that happens... is the engine stuttering, or staying smooth, and just loosing power?

Stuttering is rich

Loosing power smooth is lean.

 

[moto17]

I think it is stuttering... plugs look ok dark grey? I think I could pull the new carbs and check the jet size and compare them with the jetting in the old carbs. It gets to the 6500 real quick and smooth then just sort of acts like it is starving? but I can do this every 4 seconds...hit the power it rockets to 6500 starts to come on to plane then falls off,repeat,repeat same thing?back to 4500 and runs smooth? thanks!

 

[Dr Honda]

You didn't check the jets???? That's not good. When you swap carbs... you have to verify everything. Something like that can kill an engine.

Pop them open, and check the jets, needle/seat size, and the pop-off.