yamaha 80 to 100 H.P. upgrade

[C-WEED]

I have my carbs off doing a cleaning. As near as I can tell the only difference between the 80 and 100 h.p. engine are three parts in each carb. The jet, jet needle and the main jet. The valves and cams are the same on both versions. Total cost for parts to convert 4 carbs is about $180. Anybody here ever done an upgrade such as this?

I purchased an ultra-sonic cleaner for cleaning the carbs. I experimented with just cold tap water. In 5 minutes the carb is spotless in all passageways Really amazing to watch...

[journey on]

I guess I have a question. Is the displacement the same between the Yamaha 80 and 100? Are the bore and stroke the same? The answer should be yes, and then we can go on to the parts differences.

Those parts you mentioned just affect the mixture and I doubt that Yamaha would jet the engine so far off to lose 20 hp since it would run really badly. I would assume that the carburetor bores are smaller and the peak power is at a lower RPM on the 80 than the 100 (granted that the displacement is the same.)

That's not uncommon on outboards. The mfgs are selling you horsepower and even if it costs them the same, you pay more for more HP. Evenrude did this and the Honda 8 hp and 9.9 have the same block, etc.

You can buy bigger carburetors, but then you have to adjust the timing, etc. to the other engine specs. That engine isn't new if it has carbs on it, and how much would replacing them be?

Boris

[jennykatz]

they use a 1600 cc block on the merc 75/90 and yamaha 80 and 100 hp It sounds plausible that is how they get extra hp is through carberation and timing On the Suzuki and Honda they use the variable valve timing to get more hp 150/175 suzi or 135/150 honda . I think you would only get a little more top end out of the 100 vs the 80 you might be able to throw a better pitch prop go from a 15 pitch to maybe a 17 more speed and better economy good luck on your switch