Was watching the tach while running today and noticed that at WOT I'm only getting 2100 rpms. does this seem low? I feel like I should at least me knocking on the door if not over 3000.
1436 riveted
8x4 prop
16hp single cylindar with header and air intake (gov. Removed)

Should be over 3000


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Home built? How does it run out of the water? How is your trim tab bent and to what extent? We had this problem on a small hp longtail, and found that we had our cavitation plate welded a little too steep and our trim tab bent alot to counteract the steep part... The way I could explain it would be if you run a mower through some tall grass and it bogs down the engine because there is too much load on it... We look for about 1" to 0.5" of space between cavitation plate and prop at the peak of rotation....

I have no trim tab/cav plate on this. I try to run the prob right under the surface as high as it will go without blowing out. However after a 30 min run yesterday I am really looking to add a plate(unfortunately my frame is aluminum and I don't know anyone that can reasonably weld it).

You could drill holes in a piece of plate and drill holes to match at the end of your cavi... bolt on this plate and use it like a trim tab...

took it out for a hunt this morning, only me (180) dozen decoys blind and gun. Got up to 15mph but peaked at 2100 RPM... whats the deal? Clean the carb or something? I can only imagine the speed increase if I can get up closer to 3000.

These figures dont jive. If you have a 8x4 prop you would have to turn it 3600 to get close to 15mph. If your only turning 2100 you are not seeing all of your horsepower either. 8x 4 s usually run about 14 at 3600

These figures dont jive. If you have a 8x4 prop you would have to turn it 3600 to get close to 15mph. If your only turning 2100 you are not seeing all of your horsepower either. 8x 4 s usually run about 14 at 3600

Could I have a defective tach? It's one of the cheap Chinese ones.

Make sure you programmed your tach right. Usually when you set it up it has the "fires every stroke, every other stroke" etc which sounds like you are on the wrong one. Double that number and its right around 4200rpm, which is where most are running wide open without backing out the limiting screw or removing the govenor. What kind of tach is it?