prop ?

[buck0123]

what prop to run on a 0s .21 outboard tunnel hull?

[BoatDoc]

i would start with octura x438 or x440.

[buck0123]

thanks boatdoc it has a x440 on it when i bought it just wanted to make sure it was right

[BoatDoc]

if you're into modifying your props...you could look into cutting off some of the tongue and maybe a back cut. i was running an x440 on my lap cat with k&b motor. the prop has a barr cut, light back cut and partial tongue removal. it revs like crazy. more than enough power on a stock motor to send that thing airborne with that prop. not running nitro anymore, but i have a feeling that prop will find a home on one of my FE boats.

[Ron Olson]

You'll have to find out what your boat likes and that could vary.
Boatdoc mentioned two good ones but yours might like the X-437, X-637, M-440 or Prather 215. How heavy the boat is, the percentage of nitro and other factors will dictate what the boat likes.

[buck0123]

You'll have to find out what your boat likes and that could vary.
Boatdoc mentioned two good ones but yours might like the X-437, X-637, M-440 or Prather 215. How heavy the boat is, the percentage of nitro and other factors will dictate what the boat likes.
the boat is a topspeed 2 with a os .21. im using 20 % nitro and is seems not to rev up all the way. when i bought the engine it had a octura x440 prop. im having a hard time adjusting the carb. do you know what settings it should have.

[Fluid]

I suspect that the x440 is too much for your setup, that's a good prop for a K&B OB. The OS likes to rev, and depending on the depth and angle of the motor you are likely overloading the engine with too much prop. IME it is better to underprop a new engine than to overprop it anyway.

Alternatively, you may need to break-in the motor some more, lean it out, etc. - hard to tell from here. Likewise it is almost impossible to tell you how many turns out the needle should be since it depends on temperature, fuel, length of line to the tank, the relative height of the tank, prop, prop depth and prop angle. The most common beginner problem is running the engine too lean, this causes the motor to stall out on the water. The best solution is to find someone with nitro motor experience to help, even airplane guys. Good luck!

.

[BoatDoc]

stepping down to an x438 or one of the prop's ron suggested may be a good idea. my tunnel wouldn't even step up on plane with a 438! that's why i put the 440 on it. the same motor ran a 438 on my mono with no prob's. it's all in the set up and weight and all that happy horse poop. my new philosophy right now is to get what looks like the best prop, plus the one's on either side of it. that x637 sounds like a tempting idea too.