Motor Boggs down to half throttle after wot for a few minutes

[Maraian]

Then after 20 minutes of low rpm, I am able to full throttle again for a few minutes?
anybody experience this problem?
2006 15 hp 2 stroke tiller

 

[racerone]

Borrow another tank and hose for a test run.----------And have you inspected / replaced water pump impeller ?

 

[Maraian]

Changed the impeller 2 short seasons ago. Carb was rebuilt by a shop 4 seasons ago. I have not inspected. I am thinking it has something to do with the gas flow into the carb bowl being restricted. It can keep up with 1/2 throttle, but a few minutes of wot depletes the reservoir in the bowl and it just runs off of the restricted amount of gas refilling the bowl?

 

[w2much]

Are you sure the tank is venting?

 

[Maraian]

I will recheck the vent, but it had been running fine all day with the vent the way it was. Also there is a strong steady stream of cooling water discharged, to follow up on the first reply.
Thanks