1966 Johnson 60hp super seahorse

I have a 1966 Johnson 60 hp super seahorse that runs great at idle or in neutral but when you get it on the lake and put it in gear and floor it it falls on its face and runs like crap. It doesn't have any power and runs like it's starving for fuel or air. I've been through the carb 3 times, new float, seat, needle.. new gaskets.. I've sprayed carb cleaner through every port and orffice in the carb. (Mine dont have the adjustable high speed adjustments they are in side the carb) I've put a new filter on, I've put two sets of new plugs, I've had a mechanic set the timing back in time. I've checked compressing which was 90 on all cylinders. I've checked spark is good. Any advice would be very helpful and appreciated. Thank you!!

Open each low speed mixture adjustment 1/2 turn and try again.

I've tried that on the lake while it is running and it seems to never come out of it. It bogs down and doesn't wana Rev up to take off. Would it be a possibility with the Magento not advancing and opening the right distance? Sorry I don't exactly know much about the Magneto set up. I know it's timed right but havnt pulled the timing belt off and looked at the the advance part of the magneto.. also some one pulled the damn plug wires off and to double check my self do you know how they are hooked to the cap exactly. I can't find it in my book. Thank you

Dumb question but the Magento how it opens is that something you use a feeler gauge to see how close its opened when advanced?? If so what size feeler like 17??