Converting a 20hp Yamaha to a 25hp

[Richard]

Hi Guys,

I've heard this can be done relatively simply.

Just wondering what is involved and has anyone had it done ?

I've heard it can be as simple as removing a baffle but I also heard that it might require a carby adjustment/change.




Richard

[davo]

For 2 strokes it's only usually a carby change or sometimes only tuning. If yours is the twin carb 20HP then it would be adviced to get a shop to do it to tune the carbs correctly.

[Richard]

Yeah it is the twin carby model. Might have found someone who can do it so I'll let everyone know when i find out whats involved


richard

[Richard]

I found out that the engine just needs the exhaust port bored out a bit ($50 worth of work) and maybe a prop change, which I'm going to be advised on after the yamaha tech sees my setup.

Nice and simple and cheap (if I don't need a prop change).


Richard

[Nathanrb4]

Is this something that could be done to a 40hp yammie as well? mines only a single carbie.

[Richard]

Not sure nathan, but I do know that in my case it can't be done to the single carby model. Mine is one of the dual carby two-cylinder models (1997-8) and the guy who is going to do it stipulated.

If I remember I'll ask him and see what this guy says.. I'm not getting mine done till the weekend



richard

[waznot]

hi richard, yes i had it done to my 20 hp. the salesman told me it could be done when i bought it, but recommended to do it at the 50 hr service when they have it all open anyway, and so you could tell a difference in speed. yeah they just drill out the exhaust that restricts it. basically the 20 and the 25 are same motor. i did notice about 4 to 5 mile an hour faster i think.
i guess its worth doin.
wazza.

[Richard]

In my case, I need that extra bit of ooomph.. I have a 4.0m edgetracker with a full floor and casting platform. When I bought it i went on the recommendation of the salesman and got the 20hp. A 30hp would have been much better suited rating i think though as it was also the heavy duty model which has a heavier mm bottom (i think).

Also, the prop i have on now is a 10 1/2 pitch, which is probably not suited either to a boat which is on the heavy side for this size motor. So hopefully with the extra 25% power and the same prop (which should now be more suited to a heavyish boat with a bit more hp pushing it), I should get a bit better takeoff. I found with the 20hp, as soon as I put some weight in it it took ages to get on the plane.

If it helps with that problem - it will be $50 well spent in my books.


richard

[waznot]

after having it done to mine richo, i kid u not, it got onto the plane with 4 blokes all of us over 100kgs in a 375 dart. pretty impressive for a 2 stroke i thought! :)