OMC 25hp vs 35hp difference in parts?

[Heartman]

I'm going to try a different approach here...

Does anyone know the difference, mechanically speaking, between a 25hp OMC and a 35hp OMC outboard engine? I mean besides the 10hp difference...what are the specific differences in parts?

[PerchJerker]

I'd recommend against it, the people that I know that have done it have not been happy. The lucky ones have had their converted motor run the same as it did before (ie. the didn't gain anything but they didn't hurt anything either), but most of them have lost smooth idle and the ability to troll and have not gained anything on the top end.

[boatfixer]

Never advance the timing past the manufactures recomendation. Good way to burn the pistons up. If I remember, the main difference is the carburetor and/or the exhaust tube.

[VMS]

Hi Everyone,

I believe there are two parts in order to upgrade...a larger bore carbeurator with the correct jetting, and an exhaust tuner (right under the powerhead). It is do-able, and not very hard...the exhaust tuner is probably the toughest since it requires removing the lower unit, and the midsection along with the power head to get at it. Not hard, but taking time is definitely in order.

There can be issues to idle after making the mods, but you can get around this easily ....boyesen carbon-fiber reeds. They probably have a set for that motor which will increase your RPMs (as does the new tuner) without adjusting timing. They just have more flexibility than the stock aluminum reeds.

It will get costly to some extent, but if you like to tinker, its a fun job...

Steve

[Valv]

Let's see parts should cost around $ 500.00, gain in speed 5mph.

I wouldn't do it. You be better off finding a good 35hp this time of the year (winter) and sell your 25hp in spring, you might even make money on it.....