Yamaha 4 stroke

**Utah Scooter** · 11-13-2008, 02:13 PM

I am considering buying a 1997 yamaha 4 stroke 4 cylinder 750 cc liquid cooled motor out of a snowmobile. I can't seem to find any specs on it. Does anyone have an idea on this motor or any hp/tq ballpark guesses? Also, would this be a better motor for a mini than a two stroke twin 800 cc from a snowmobile? I'll be building a belt reduction drive for it too. Give it to me straight. Thanks . . .

**Spyda-Ryda** · 11-15-2008, 01:32 AM

I'd have to say go with the 2 stroke, but that's just my two cents...... From my experience and knowledge, you'll probably end up with a better power to weight ratio. I know the 4 stroke would be better for the environment and probably bettter on fuel economy. But I'm a power, speed, & horsepower junkie. haha! Although, there are many things to consider.
1. What do you expect from this set-up?
2. What are you trying to gain? Fuel economy, horsepower, weight reduction, etc...
3. Is the new motor carburated or fuel injected?
- If electronic injection, do you have someone available to do necessary changes to programming or electronics?
4. What is the RPM range of the power curve of the motor? You will need to know this to be able to figure out your
necessary belt reduction ratio, prop size, & pitch.
5. What kind of conditions will you be using the boat in? Water running, ice, snow, dry ground, sticky grass... etc....

There are many factors that come into play.
I ask you those questions because I am asking myself some of the same exact questions.
I've come to find out by my own experiences that experimenting with something that has not been done yet can be very satisfying if successful, but can cost a whole hell of a lot more than you would expect.

As for the specs, I'll see if I can so some research tomorrow given the information that you posted on the 4 stroke. If I were you, I'd do alot of research before you start buying parts. If you know any snowmobile technicians, that would help you out a bunch. Especially a yamaha tech. They know these motors best. I'll offer whatever information that I can come up with and give my opinions if you want them. I'm no expert and don't claim to be, just have a lot of airboat experience. If I had all the answers....... I'd be building, selling, and racing them myself.

Good luck to you my friend and if I can help in any way, give me a shout! Please keep me informed on the details of this.

**Utah Scooter** · 11-15-2008, 11:52 PM

I did some more research and the sled hae has isn't made with a 4 stroke motor. It's a 2 stroke 4 cylinder. Would that put out more torque than a 2 cylinder of the same size? I can get an 800 cc motor (complete snowmobile) for about 1500 bucks.
I am probably going to build a 14x6 foot boat with polymer to run mostly water, snow, and ice. Some sticky mud, sand and grass. 2 or 3 people.
I'm thinking of using a 70 or 72 inch warp drive and pitch it so the motor tops out around 7500 rpm's.
I need to get all the planning done so when I sell my current boat I can get right on it when I get some money. Thanks for the tips . . . keep 'em coming.

**Matapatos** · 12-06-2008, 07:29 PM

Scooter, sounds like a sweet setup you got going there! Maybe you can find someone that can help you put it together!

I think I know someone that would... I think the 800 setup would be the best. If I can finance one, I'd build that same boat, only 5'X14'. Then I could shoot smaller channels that will all be choked up, or nearly so with phragmite this coming year. The top of the boat would be 6' wide, but the bottom, 5'. Then you could still run a 72" prop. pm me and we'll talk some more!

**Utah Scooter** · 12-10-2008, 08:08 PM

It's hard to decide how big to go because a 14 foot boat only weighs a little more than a 12 foot boat and it would be a piece of cake to go just a little bigger when you are building it. A 6 foot wide boat would be only a little heavier than a 5 foot wide one. I don't know. Good thing my boat hasn't sold yet or I would have to decide all these things. After it's done it's a little tough to add 2 feet to it because it isn't long enough. I'm thinking 14 x 6 with an 800 belt reduction on it. 180(ish) horsepower. Motor probably weighs 100 pounds. Is that still considered a mini? I just want the width to get up on plane easier and the length to put stuff in. I don't know. What do you guys think?

**Papee** · 12-11-2008, 10:26 AM

Scooter I'm running a 16x5 aluminum hull with a 084 direct drive. It's probably close to the same amount of surface area in the water. My boat runs fine with two people and gear at 20+ mph and a top speed of 40mph with one person in shallow water. I'll be changing props over the winter so my speeds will be a little better. The size of the motor determines if it is a mini, not the hull size.

**Spyda-Ryda** · 12-16-2008, 11:48 AM

Hey scooter,
Are you sure on that horsepower? I thought an 800 HO was the following Rotax motor, see specs:

Engine Type 793 HO

2-stroke
2-cylinder
103 kW/140 HP
799 ccm
Liquid-cooled
Reed valve-controlled

**Utah Scooter** · 12-16-2008, 11:23 PM

I haven't narrowed it down to a specific manufacturer. Polaris, rotax, arctic cat, yamaha. . . . . not too much different. You can get more hp if you pipe them. I was just guessing high on the power one of those motors puts out. I'm just dreaming unless I can sell my boat soon. Heck of a time to be selling something like that. I have only had 4 or 5 people even call me on it and only two that went for a ride. The first wanted it bad but it's not big enough for him. The other guy wants it bad but has to sell some stuff to come up with the money.