I've been reading the forums on this topic but still have a couple questions. I have 2010 tohatsu MFS9.8A3EFS model and am interested in the HP increase modification I've read about. I've read that simply need to replace carburator to 15 HP model and that's all. But when I look at Tohatsu website the specifications for the 9.8 and 15 HP are quite different.
-209 cc displacement
-351 cc displacement
I don't understand how the 9.8 can develop the 15HP with 140 fewer cc displacement? Also the weight difference is a concern. The 15 HP carb isn't going to weigh an extra 30 lbs, so that means that there are addtional differences like shafts, gears and other components that would need to be bulked up on the 15 HP model? It just doesn't add up. Thanks in advance for all the information on the forums, it is a great resource!