WOT problems on 07 Yam w/ 115 4-stroke on 19 ft Grady

[mako172]

I am looking to buy a 1991 19ft Grady Explorer with a 07 Yamaha 115 4-Stroke on it. The owner let the fuel in it go bad and had to replace the tank, hoses, injectors, fuel pump and TPS ($$$$ - saw receipt). I know the boat is underpowered with a 115 but it feels like it still has issues. When running the boat at 3/4 throttle it goes 30mph at 5200 rpm w/ a 17p aluminum prop. When I move it to WOT it feels like it looses power and speed. The motor feels a bit hesitant, like it is not producing quite as much power as it could. Sometimes I feel like I hear the pitch of the engine go up and down but I can't pinpoint it for sure. What could the issues be? The guy is offering it to me for $6k w/o trailer and the mechanic is willing to stand behind the work if it is related to what he did.

 

[rodbolt]

Re: WOT problems on 07 Yam w/ 115 4-stroke on 19 ft Grady

sounds like it still has some fuel issues.
if it cant turn at least 5800 RPM with the load that day someting is wrong.
a quick run up with test wheel YB1624 will tell the story.
it should spin that test wheel 5600-5800 RPM.
if it can chase hull and prop issues.
dont buy it until it runs properly and can reach 5800-6000 RPM and all leak down test numbers are less than 15%.

 

[mako172]

Re: WOT problems on 07 Yam w/ 115 4-stroke on 19 ft Grady

I really don't have access to much test equipment and the boat is on a lift where it is difficult to work on. What is my best bet for testing it out?

The 5200 RPM's were with 2 people and 20 gallons of gas. When I run the numbers the aluminum prop is producing a 23% slip. Given that the boat is underpowered, would a stainless prop and hydrofoil help? I'm wondering if the undepowering is the real problem.

 

[rodbolt]

Re: WOT problems on 07 Yam w/ 115 4-stroke on 19 ft Grady

under powered shumder powered.
the motor is SICK or WAY over propped which WILL lead to DEATH.
either make sure its running correctly according to my ABOVE test wheel post or accept the fact that a head and block assy will set you back about 5200 dollars installed.