2008 yamaha 70hp 2 stroke boat to pontoon issues

[Bigshannon56]

I have a 08 70hp 2 stroke yamaha that i bought brand new in 08 and had it mounted on a 16' fiberglass nitro fish and ski boat. It came with the yamaha controler with the side lever throttle lever, im not sure of the number. I never had a tach hooked up to it, so the previos 8 yrs worth of max wot rpms history is unknown. But, it always sounded to me like it was pretty much always running wide open with the throttle maxed out on the controller. Benn well maintained but never any carb service, my theory is if it aint broke dont fix. Lol. Although i also know preventative maintence is critical on any outboard. Ok so we run the boat in early april, she starts up, runs, hits wot on the river as she always has. So, we buy a g3 suncatcher 22' pontoon that does not have an engine on it, and we mount our 70hp onto it. The pontoon has all the hookups already on it for yamaha outboards, it had a 90hp 4 stroke on it. Only it has a 4 prong connector that i cant seem to find on my engine to hook it up to. The pontoon has the yamaha 704 controller, a bit different than my controler that came with my outboard, which i left on my boat when i sold it. Ok so everything hooks up like it should electrically, except for this one plug coming from the bot to the motor. We mounted the 70 in the same height position that the 90 hp sat on the pontoon. Did not change prop. Its a 13.5 x 15 k. Had to adjust on the throttle link to get it right. And the timing indicator seems to line up with both marks in neutral and when the throttle advances Tachometer is set to 6p and is hooked to the geeen wire coming off the controller. Its wired properly. Installed water fuel seperator, no leaks from the carb back to the tank, its gettin fuel best i can tell. So we take it out, she starts and idles, shifts into foreward and reverse just fine as always. Shows to be idling at 700. We take off, all is well. Rpms max out wide open at 2800 and speed shows 13 on the guage. Engine is not running wide open, and the boat seems to be lunging a bit and and doesnt seem to handle smoothly as far as it wanting to pull on way or the other slightly, espiciaally when in somewhat swifter current on the river. Now keep in mind just a day prior, this same engine was on a nitro boat, running 40mph wide open and handled like a dream as usual. So whats wrong with my setup here?

Possible carb issue?
Wrong pithch prop?
Motor mounting heighth?
A combination?

Before i go to yamaha, id like some advice if any of yall have any. Maybe its something simple. Thanks!

 

[tommarvin]

Maybe post some pictures. A picture is worth a thousand words here.

 

[ondarvr]

You will need a prop that is very different from the one used on the Nitro.