My dad's boat has been doing this for a while now. I was hoping the problem would go away when I replaced the float and stopped the leaking issue.
It starts and idles great now. You can rev it up in neutral with no problem. When you put the throttle down in gear to try to get up on plane it bogs down and will die. My dad discovered that if he taps the choke when it starts to bog down that it will pick up rpms and get up on plane if you time it just right.
When I took it out for a test spin on Sunday evening I had to engage the choke and hold it closed before it would get up on plane. After it was up on plane, I could let off on the choke and it wouldn't lose rpm's. I only tried it a couple of times before I put it back on the trailer. After running on plane for a few seconds and pulling back on the throttle to come off plane it would die again...
Here's a short video that I took of it getting on plane. If you listen closely as the beginning of the video, you can hear the engine start to rev and then bog. Then you hear the click of the choke engaging and it jumps right up on plane...http://smg.photobucket.com/user/bassser/media/2013-05-05201842_zps3332186e.mp4.html
My first thought is a vacuum leak. If it was a fuel supply problem, I can't imagine that it would have as much power as it does after you choke it. Could I spray some carb cleaner around the carb flange like you would on a 4-stroke to see if it's sucking air there without damaging the motor. I guess it would be better to use deep creep that has some upper cylinder lubricant in it...
I'm pretty sure the idle adjusting screws are adjusted right, but I might try to play with those some. I guess maybe back them off 1/4 of a turn at a time.
Any other suggestions?