I have an 80hp four stroke Yamaha that had been sitting a while. I just had carb kits put on all four carbs, new impeller, plugs, and new filters. I think that is all that was done to it. I took it out for the first time and the motor purred like a kitten, idled perfect, ran absolutely perfect at every speed except full throttle where it started to cut out or bog down. Pretty sure it's starving for fuel. I am no mechanic but was wondering if there could be things I could try and at least rule out. I bought a new Yamaha brand fuel line and primer bulb today to replace the new generic one that I had put on previously.

sounds like it's starving for air.

How do I get it more air? All the filters are new, guess I could take the gas cap off of the tank?

i had a 15 hp johnson that was doing the same thing. i cleaned the carb twice, same thing. took it to a local shop and they changed the jet in the carb. said it wasn't getting enough air at full throttle, which is where you run a 15 hp just about all the time. when i called him about it he asked me to pull the choke out when it started bogging down. if it started running better, it was starving for gas, if it didn't run better, it was starving for air. i dunno, but it ran great when i got it back. i sold it to the kids across the canal and it's still running great. good luck.

I have the choke that operates by pushing the key in when starting. I tried to push it in when I was at full throttle and no difference.

I would check the fuel pumps for contamination or hard diaphragms. If they get hard from age they will not pump enough fuel for full throttle. Here: http://www.boats.net/parts/search/Yamaha/Outboard/1999/F80TLRX/FUEL%201/parts.html

I replaced the primer bulb and fuel lines to and from tank and motor and that seems to have fixed the problem. Thanks for the responses.