90cc sno scoot

[scoot218]

Hello Everyone,

Thanks to an article I found on this website I recently did a 90cc (apex MXR)  motor swap into my Yamaha sno scoot. If your not familiar with the Yamaha sno scoot global.yamaha-motor.com/showroom/cp/collection/snowmobile_snoscoot_sv80e/  heres a little info. unfortunately I'm running into some gearing issues that's considerably limiting my top speed. I guess the easiest way to explain would be if you were to take your wheel off a scooter and replace it with a 5'' wheel.

The motors transmission is geared for a front and rear sprocket that is turning what I believe is a 10'' tire. This was just an oversite on my part. what I did is basically mounted it up directly to the 5'' driver which turns the snowmobiles track. Clearance is going to limit how much larger of a driver I am going to be able to use so a driver swap may not be an option.


So I'm wondering if anyone may have some ideas on how to tackle this issue. preferably I would like to see at least 40mph. Im running the stock pipe (which I had to modify to fit) so my best guess is that I'm at somewhere around 10rpm and 8ish hp.

Thanks! 

[2stroked]

I know what you're talking about, but your link is taking me to a Yamaha page with a 404 not found result, I'm on mobile if that helps.

There are gear kits, but having the 5 inch driver is a limiting factor, you're right.

[scoot218]

yeah just noticed that link didn't work. I just spoke to a gentleman at west coast quads. He said the stock apex mxr uses a 32 tooth rear sprocket and its about 7" diameter. If you lose around 5mph per inch of tire or in my case sprocket/driver I should be about 10mph off top end with my 5" snoscoot driver if that makes sense.

Right now im only at about 25 but I think I have some other tuning issues going on. I think I would be closer to 30 if it was running right. Any ideas on gearing and other mod options for these 90's would be greatly appreciated. Im going to have a custom pipe professionally made by a local guy in late march. Im thinking that and maybe a mild bore and ignition this summer and then its just figuring out the gearing issue and I should be in good shape.

[190mech]

Port layout and combustion chamber design varies wildly with the 90cc motors..That all needs a close look and adjustment to get a strong running 90cc 2stroke!

[ryan_ott]

Besides the sprockets you have gears under the trans cover that will affect the overall gear ratio. Get it running well - check squish and port timing, find a pipe to match. Ignition if not rpm limited should probably be ok.

[scoot218]

thanks for the feedback guys! I purchased and installed the malossi 15/41 gears for the transmission and didn't notice any top end gains. I'm thinking this is another hint that I need to address the pipe and overall set up and get it running correctly before I try to modify it for more power/speed. Im lucky enough to have a shop that about 30 miles away that builds 2 stroke motors along with custom one off pipes. I think its time to drop the scoot off with him and see what he has to say. I will keep ya updated with the progress.

[pitobread]

Is yours an old sno scoot or a new one?

[snaker]

Well if the engine is spooling up to your desired rpms (tach meter) but not top ground speeds, then engine is not the problem. Gearing too low.

If the engine is not getting up to rpms, then its engine / hp issue.

[Zino]

Snaker nailed it .
If a better gear ratio doesn't change your top end .

Boosting Horsepower is the key.
You can increase compression by decking the cylinder head.
A better pipe will do wonders to boost horse power.

[scoot218]

My Sno scoot is 1990. I have installed the mallosi taller gears and didn't see any difference. I don't have a tach on it but it definitely feels that its running out of gear. I want to start with modifying the gears before the motor because to me that's what it feels like, a gearing issue. My problem is is that im not having any luck finding any different gearing set ups other than the mallosi. The motor is from a apex mxr race quad.

[snaker]

You might like this.




I had my eye out for one of the big ones for years. They weren't common in my area. Any chance you have a spot to add in a chain/sprocket set into the driveline?

[dexameth]

Ha! My first motorized thingy ever! I had a snoscoot for a few years as a child... then my dog ate all the intake hoses and my dad sold it ): that thing was so fun at 10 years old...

[repherence2]

Feb 10, 2020 9:46:42 GMT -5 scoot218 said:

My Sno scoot is 1990. I have installed the mallosi taller gears and didn't see any difference. I don't have a tach on it but it definitely feels that its running out of gear. I want to start with modifying the gears before the motor because to me that's what it feels like, a gearing issue. My problem is is that im not having any luck finding any different gearing set ups other than the mallosi. The motor is from a apex mxr race quad.

What about a gear set from something like a Polaris 90?

[ryan_ott]

Looking at eBay and partzilla I think the original motor is based off of a Jog/Prebug. Any reason for not freshening that up? With some pictures we could help find you a variator and possibly gears.

[scoot218]

Thanks for all the replies! So Just to clear a couple things up. The original motor from my sno scoot was an 80cc 2stroke that was used in the Yamaha riva scooter in the 80’s. These were known for being very de-tuned gutless motors that were originally around 4hp. www.motorscooterguide.net/Yamaha/Riva80Beluga/Riva80Beluga.html

I swapped this motor out for a 90cc out of an apex mxr race quad youtu.be/2QrqVwBcnWA

Liquid cooled high performance race motor with a top speed (50mph) twice as fast as the original (25mph)

Problem is is that I’m going slower now than before but I’m getting to top speed very quick.

I’m thinking the problem is is that the new motor is geared for turning 2 sprockets like on a quad or dirt bike and now it’s directly turning a 5” driver which turns the snowmobiles track.

So if I’m thinking of it right, which I very well could not be lol. The main drive shaft is turning a 5” wheel(driver) instead of a 10” wheel on the quad.

I hope that makes sense! And thanks in advance.