TOPIC: 1963 Mercury 500 having top end problems

Well rebuilt the fuel pump and cleaned the filters on the 2 carbs, also ran a gallon of fuel with Seafoam in it. Runs much better but still the problem as follows.
Start out of hole shot, jumps and plane and runs like a bat out of hell to about 30 mph (don't have tach), then after a little while seems to start slowing about 1/2 speed it runs fine there but won't accelerate again until I slow way down for a bit, then repeat!!!!

I am using an Attwood tank, it's a no vent tank and I am now starting to wonder if thats killing the top end after too much suction. Have not tried to remove the cap yet, need to get a rag or something to prevent a spash first. Just wonder if anyone has had a similar problem.

I experimented putting the motor at different tilts and found the best postion, not too much nose up and jumps on plane very fast, everything is working so perfect but this.

I assume it's not a dirty carb problem since it runs great everytime I slow down and start again.

call me 1 914 310 7086 . take the cap off. I had that problem on a new motor years ago that is why I want you to call.

I would try just loosening the cap. It doesn't cost anything and if the fix is that easy then you've dodged a bullet.