90 Yamaha fuel issues at WOT

[ShopSecretary]

I have a customer who has a 90 Yamaha. Engine runs great at low RPMs. When he goes WOT the engine starts wanting to bogg down like it's losing fuel. Changed the fuel pump, cleaned carbs, and swapped gas tank (same lines used). Can anybody help me with this? Customer noticed inline fuel filter low on fuel.

 

[99yam40]

monitor fuel pressure and vacuum to see if it has a restriction or maybe sucking air.
Some shops have fuel testing equipment that will test flow without even running the motor to see if it can flow the proper amount.
if you do not have this then running it with a test wheel in a tank may be in order or out on open water with your equipment hooked up

 

[jakedaawg]

2 stroke, 4 stroke, is 90 the year or the HP?