why does my 1974 2 hp go faster than my 1974 4 hp

[Eric1207]

These are all Evinrudes: I have a 1974 2 hp mate. I tried out a friends 1974 4 hp yacht twin and the 2hp made the boat go faster. Same boat, same gas. The 2 hp made my 8.5' inflatable plane slowly at around 7 knots, the 4 barely got it on a plane. The 4 also did not seem to wind out on RPM like my 1980's 6 hp does. I had hoped to get some significant speed increase by doubling the hp to 4, maybe even get on a plane with my 100 lbs wife also aboard. Now I may stick with my 2 if there is no speed advantage. My 6 hp winds out real nice on a plane with 2 or 3 people but it is too heavy for me to conveniently move on and off my dingy frequently.

So can you tell me why the 4 hp does not make the boat go faster? Is the 4 hp geared or propped to push a heavier boat, (it is called a yacht twin)? Or is the 4 hp I tried out not operating correctly?

Wouid a 1980s or 90s 4 hp do any better?

I really want the 4 but if its not going to do any better then I guess I'm stuck between my 2 and 6 engines.

Thanks, Eric

[boats.net]

The 4hp may have wrong prop to perform well on your boat or possible the 4 has a problem and not reaching full power.