2005 Yamaha V MAX - Motor ball is not staying hard

[tuccimf1]

The boat gets on a plain at 43 RPM for about 15 seconds then the RPM goes to 28 and the motor cuts off. I have changed all the hoses including the gas hose from the motor to the gas tank.

This did not start until the mechanic put on my gas sender unit.

Can anyone tell me what maybe wrong with the motor?

[DennisG01]

This may be really tough as there is limited information here - which tends to lead to a lot of guessing. The info provided is also not very descriptive or accurate. For example... "gas sender unit" sounds like a fuel sender, which would have nothing to do with a running issue.

And... "motor ball"... what the heck is that? I'm going to assume you are referring to the fuel primer bulb. So, if that is getting soft and you are losing power, you may have a restriction somewhere in the supply side - which can include the pickup tube and the vent line. Try running with the fuel fill cap off.

[panasonic]

Perhaps Mr Mechanic who changed the fuel sending unit dropped a rag or something down in the tank. And it is now across the pickup tube...restricting fuel flow.
I would almost bet $20 on that.

[99yam40]

more than likely there is an air leak where the fuel line comes out of the tank, the motors fuel pump sucks more air than fuel.

[tuccimf1]

Could it be the fuel pumps? The motor sat for a while before we purchased it.

[tuccimf1]

Also this did not start until the fuel sender unit was repaired.

[99yam40]

Also this did not start until the fuel sender unit was repaired.

if that was the last thing messed with before the problem , I would look at that area first.
but sitting for some time could cause other things too

[panasonic]

Try running it off a portable 5 gallon tank, take the boats fuel tank out of the equation. See what happens.