SnoScoot Clutch Mods

[Sumac Motorsports]

There has been some talk of clutch mods on the Scoots so I thought I would post some info on what we have done to ours. I'll start with the secondary because that is what I have apart at the moment. I'll post in the future of the other mods when we do them.

Removed the Secondary from the machine.

Remove the nut that holds the shoes part to the pulley, threads are normal (lefty loosey) be careful, spring will pop pieces apart (spring removed in picture). We used a 1/2" Air Impact with a big socket to get apart.

Part seperated

Removed small springs so shoe can be opened up for grinding. Took part to belt sander & sanded the pointed end flat removing material to lighten up

Comparison of lightened vs. normal before going to belt sander.
We didn't take off much but it sure seems to help give it that little extra rev before the track starts to move. The shoes on the clutch are all worn to nothing in the pictures, new one is on the way, just wanted to show what we do to give a little extra kick to help spin the track after we do the 121 conversion.

 

[utah340six]

clutch mod

thanks a lot.
so this helps the rpm stay a little higher before it starts to move ?
correct:
any ideas on high end like belt not getting to top of cluch for top end ?

 

[Sumac Motorsports]

Top End?

That is the next part of the puzzle, we are going to lenghten out the slots on the secondary to let the pulley get closer together.......I'll take a few pictures when we do that.

 

[07SummitX800R]

Thanks! Keep em coming. Clutch theory is something I've never really understood except that the weights and springs move in relation to each other at different RPM's... Crazy stuff.

 

[volcano buster]

I guess I'm a little concerned about this method.

I picture the lighter shoes allowing the belt to ride up in the pulleys before it engages. The secondary clutch will be spinning faster when the shoes finally decide to engage possibly causing more slippage. This will also get the clutching into an effectively higher gear before engaging as well.

I'm more inclined to think that having the lighter high-elevation weights in the primary will allow a higher stall speed before the clutches start to move up (creating more power at a lower speed) which should help the lower take off needed to spin (turn) the larger 121" track.

I say this, because I think the clutches need to stay in as low of gear as possible until everything is moving, then let the motor rev to build up ground speed.

I have no experience with clutching these things so I am simply going on what my mind tells me.

 

[07SummitX800R]

I'm beginning to think a lot of the problems with track speed and clutching have to do with jetting. As I mentioned before, I was running the stock 103.8 main and 62.5 pilot at 6000' (and was spitting oil out the exhaust like crazy) and the manual recommends 100 main and 65 pilots for this altitude and temp. So, I went to the dealer today with jets in hand and had them match me up with 102.5, 100, 98, and 97.5 main jets, and a 65 pilot. Got home and started with the richest main and started doing WOT tests and the track speed and shifting improved with each jet change. I finally settled on the 97.5 as it game me a nice golden brown wash, and the track speed and overall running quality and performance difference was night and day. They say start with the simple things first, and I think with the high altitude rollers on the clutch, and the jetting changes I made, I may have a winning combo here. I'm going to take it up to the hills and try and do a few runs on it to see how it runs on snow, but the difference I've seen on the track stand was impressive. It's burning a nice blue smoke out the exhaust, and isn't spitting oil out the pipe like it was before. I think it was just running so rich from stock that it never had a chance to get into optimal peak RPM range to spin the track and get the clutches where they needed to be.

 

[volcano buster]

Do you have a chart for jetting these things?

 

[07SummitX800R]

I went off the service manual, but found the settings they suggested to still be too rich. I suspect that's why the previous owner was running a BR6HS plug instead of the BR8HS stock plug. After changing the jetting, and adjusting the gap in the plug per the service manual, it's a totally different machine. I'm seriously amazed. I wouldn't be surprised if it pulls 30-35 mph with the jetting changes I made, and the HA rollers on snow.

 

[07SummitX800R]

 

[07SummitX800R]

By the way, the previous owner was from Oregon, and was still running the hotter BR6HS plug to compensate for the jetting, so I would imagine even at your altitude, if you still have the stock jets, and are getting unburnt fuel in your exhaust, it's probably too rich like ours was.

 

[volcano buster]

How hard were the jets to source? Were they used on other models so they are on hand, or simply that they fit scooters too that they have them in stock?

 

[07SummitX800R]

Easy. They are standard Mikuni Carb Jets that fit many other bikes, atv's, etc, so any dealer should have some variety of them. I went to three different dealers and they all had different ones I needed. One of them even came from a Honda dealership, as they use Mikuni carbs/jets, etc in Hondas as well. The one I ended up using was one of the jets that a dealer near my house gave me for free. The other two I paid $12 for total. The pilot jet was a little harder to find, but I wouldn't be as concerned about the pilot of you can't find it. If anything, it seems to run a little rich at idle, and the stock pilot would have probably been sufficient and easier to fine tune. It was $5.

BTW, if you'll PM me your email address I'll email you the service manual in PDF format for reference on anything else you might need.

 

[Sumac Motorsports]

Opps....

That is the next part of the puzzle, we are going to lenghten out the slots on the secondary to let the pulley get closer together.......I'll take a few pictures when we do that.

Sorry Guys, I ment to say "let the pulleys open up further" not get closer. That will let the belt go deeper in the secondary to give the Scoot a little more top end......

 

[Sumac Motorsports]

Clutch Mods????

I thought the title of the thread was about Clutching........ some how it was stolen by the Jets (not the football team....) Just kidding, LOL....

So to the comments about lighter shoes. Along with lighter shoes we are working on a stifer spring in the secondary. Unlike "normal" CVT systems the belt is always spinning on the Scoot & the shoes are what engages the track. The systems are a little bit more complicated then on a big sled. With a stifer spring in the secondary it should slow down the shift. There also needs to have some mods done to the primary to get the belt deeper on the primary to start out in a lower gear (opening up the pulleys) if that makes sense to say it that way. We want to set them up so they don't bog out on bottom end. We are also at sea level so our Scoots will act a bit different than in the Steep & Deep!

 

[07SummitX800R]

Sorry for the hijack. I just thought I should mention it since I had asked you in another post about the clutching, and figured anyone in my position would be interested in "less invasive" and simpler fixes than digging into clutches that require a lot more in depth knowledge of clutching theory. Clutch away!

 

[07SummitX800R]

Having said that, every bit of information I've read about clutching snowmobiles has said that unless your motor is hitting peak HP and power band, you can spend way too much time and money chasing clutch problems if you don't have the power to spin the track. I still believe these little machines are jetted too rich from the factory. FWIW I think it deserves consideration and has every bit as much to do with clutching as anything else does.

 

[volcano buster]

I viewed this a "post-long-track" tuning thread. Now that the hard part is done, what does it take to make these little 80cc engines perform. If some of it can be gained by clutching tweaks and some can be gained by jet changes, then we all win.

I am interested in hearing more on the clutching as this is a different type than I am used to playing with. The owners manual I was just scanning through said engagement RPM is 4000. It must top out at ~7000 maybe, so that isn't a lot of room for this little thing to make a lot of gear changes and operating well with a large track and possibly high elevation.

 

[utah340six]

primary clutch

tore mine apart replace jets with 65 pilots 97.5 main.(pilot is hid under black plug)
thats what was penciled in in my owners manuel.
didnt check what was in there just changed them.
took primary clutch apart only 3 rollers in it not 6.
high altitude rollers are bigger i mic'd them to see.
started it before putting cover on and my belt rides low on secondary clutch.
any help there.( like 1/2 inch)
this would be like starting out in 2nd gear in a car.
on my 700 1/8 makes a difrence.

 

[utah340six]

clutch mod link

Read this link
http://www.apexatv.com/techsupport/apexclutch.pdf

 

[utah340six]

link copy

CVT Clutch Tuning Basics - Part 1: Background and Basics

all of it did not past go to link