50hp Losing prime!! I need help!!!

[lildevil52]

I have a 1988 yamaha 50elg. motor sat for a few years before i purchased it. it ran ok but carbs needed rebuilt. done that runs really good now but after running a hour or so it loses prime. if i keep squeezing fuel bulb it picks back up and runs good but have to continually squeeze bulb. i was told fuel pump was bad so i put on a new one. no change still have same problem. ive sprayed carb cleaner around everthing with motor running but cant find any leaks. anyone have any ideas? THANKS FOR THE HELP!!!!!!!! (this one has me stumped)

[99yam40]

hook up a fuel pressure/vacuum gauge to the fuel line at different points and see if you have a restriction and see if the fuel pump is pressuring up the system properly.

Have you checked the compression on all cylinders?That is what I always do when 1st troubleshooting a motor.

[lildevil52]

compressions good 132-135 in all three holes. havent checked fuel pressure yet. i'll have to do that. but runs good for first hour or better. THANKS!!!! going to find my fuel pressure guage now

[mitch]

is the air bleed screw on your fuel tank open

[lildevil52]

doesnt have bleed screw. i just losen the cap. just bought a new gas tank today hopefully i'll get to try it out tonight . THANKS FOR THE INPUT