Ok so I know this question has been asked a 1000 times if it's been asked once. I have an '81 Evinrude 25HP. In my research for the '81 year model everything associated with the power head between a 25hp & 35hp is exactly the same. That is, the crankshaft, pistons, rings, all bearings & seals, block, intake, flywheel, etc., with the one difference being the carburetor.
Where the difference comes in, is starting with the driveshaft then all the gears in the gearcase, and the fact that a 35hp is a through hub exhaust and the 25hp is not. Also, per the manual the timing on the 25hp is to be set at 34 degrees and the 35hp
is to be set at 30 degrees.
So my question is, if I were to ever consider doing so, would buying a 35hp carburetor and retarding the timing down to 30 degrees provide me with a 35hp motor. Is the driveshaft and gears on the 35hp simply beefier or are the gear ratios different such that simply changing the carb & timing wouldn't produce the same results as a true 35hp.
Please keep in mind this is all out of simple curiosity, I don't see that I would ever consider doing this. I've put to much time, effort, and money into re-building my 25hp to ruin it.
Where the difference comes in, is starting with the driveshaft then all the gears in the gearcase, and the fact that a 35hp is a through hub exhaust and the 25hp is not. Also, per the manual the timing on the 25hp is to be set at 34 degrees and the 35hp
is to be set at 30 degrees.
So my question is, if I were to ever consider doing so, would buying a 35hp carburetor and retarding the timing down to 30 degrees provide me with a 35hp motor. Is the driveshaft and gears on the 35hp simply beefier or are the gear ratios different such that simply changing the carb & timing wouldn't produce the same results as a true 35hp.
Please keep in mind this is all out of simple curiosity, I don't see that I would ever consider doing this. I've put to much time, effort, and money into re-building my 25hp to ruin it.