Yamaha 50HP 2 stroke stalling at WOT

[Red2500]

I just purchased a 2002 Lowe 160W with a 50HP Yamaha 2 stroke. The problem I'm having started the second time I took it out this year about 3 months ago. The engine starts up no issue just a little bit of smoke. I can drive it WOT 2 miles across the lake with no issue. I turn it off and Troll/Fish for and hour or two and it will start right up no issue. As soon as I get it up to plane WOT it will start to spudder and stall out. It starts right up and will run at half throttle just fine but as soon as as get it back up to WOT it will start to die again. I re prime the fuel bulb and it seems to take more pumps than usual to get hard. Once it gets hard again it will fire up run at WOT for about 30 seconds then start to spudder and die again. This seems to only happen after the boats sits turned off for about a hour. In the morning it runs just fine when I first start it up. I thought maybe a bad bulb and fuel line -replaced. Fuel Filter - replaced. Fuel pump - replaced. Not sure what to try next.

 

[99yam40]

check for an air leak maybe.
testing fuel pressure and vacuum may be a good idea if pumping bulb helps

 

[Red2500]

Update: I tore apart the carbs and cleaned all the jets with carb cleaner. I took it out on the lake this weekend and once again it ran great most of the day then all of a sudden when I tried making a run across the lake it started spuddering. I throttled down and it didn't stall but almost did. Then it started running fine again. I shut everything down and tried to prime the ball to see if maybe it was flat and had to squeeze it about 50 times before it got hard. (arrow was pointing towards the sky),.Should the prime ball take that many squeezes to get hard? I know after running it the ball doesn't or not suppose to stay hard but it seems like it shouldn't take that many pumps. Before I put the boat in the water it only takes a few pumps and its firm. Does the length of the hose make any difference? Also I noticed the battery gage was fluctuating. Some times it stayed at 12.5v then sometimes it jumped to 14v could this be a electrical issue?

 

[ondarvr]

The length of the hose doesn't make a difference, an air leak will, and that's what it sounds like.

 

[Red2500]

How do I check for a air leak or were to begin?

 

[99yam40]

look in the frequently asked questions section of the forum for testing fuel system

 

[Searay45]

If ethanol gas has been used in it, it is possible the inside of the bulb and/or the hose have deteriorated and are collapsing and restricting flow. Be sure and check that as well.