driven clutch

[agetnt9]

Have a pink spring at 60 % (3,3) 43 deg. helix. Back shift is to fast up shift to slow. (hits rev limit when squeezed) Can i go to 50 % (2,3) ? Or will belt slip?
Or should i get dif spring? Main Question , What is the dif between dif spring and putting the spring in a dif. hole or is it the same thing? thanx

 

[PeeWee86]

You are asking for the difference between a spring pretension and spring rate? If you can visualize the spring force vs. movement on an X and Y axis, the rate is the slope of the line and the pretension is where the line would cross the Y axis.

Back shifting too fast? I’m not sure that I think that is possible. In my mind instantaneous would be ideal. With a 43° helix I’m surprised that you think that you have great back shifting.

For the time being I would recommend that you leave your driven clutch alone and add weight to your primary clutch arms to address the over rev. If you have a tight budget this can be done with your factory Yamaha arms, but it is much more simple with a set of aftermarket adjustable weights. They can be obtained from many sources for less than $200. There’s no need to waste your money on a $300+ clutch kit if you are willing to take the time to learn how snowmobile clutches work. Like everything else on your snowmobile, if you are unwilling to do it yourself there are plenty of people that are willing to take your money and fix it for you.

You were not clear on whether the over rev is constant throughout the entire shift curve or only at the start or at the finish. The more descriptive you are the easier it will be for others to assist you.

 

[agetnt9]

Thanx for getting back to me.. If i speed up slowly it will run about 80 or so. just can't punch it and stand it up as it will fall on its face. When i am coming to a stop on hard pack, it shifts down like a 4 speed car if you let out the clutch in a lower gear. at about 8-12 mph . It slows the sled down. Do you think that is the ridge on the weights.
What do ya think about Bikeman weights do the have the same curve or are they flatter than stock? I ride 90% woods 10% trail at less than 1800 ft. more like 800 ft . Thanx again for your help.

 

[PeeWee86]

Obviously you a going to need to address the overrev condition I’ll get back to that in a minute. What you were describing as back shifting I believe is engine the braking that is inherent in all four stroke engines. Search engine braking and read a few threads about it. I think of back shifting when you are running fast down a groomed trail and you turn on to an unplowed fire road with a foot of fresh heavy snow. Your clutches need to react to the new increased load. Good back shifting might drop the engine speed by 50RPM. Poor back shifting might drop the engine RPM by 600 RPM. Another example would be when you drop the throttle coming into a turn and then hammer down coming out of the corner. Is there an instant response or is there a lag before the RPMs begin to climb? This is the difference between well rounded clutching and a poor clutch setup. Theses differences may never show up in a side-by-side drag race.

To answer your question I have no personal experience with the Bikeman weights. I wish that I could recommend them because I consider many of their staff members to be friends. The co-owner, Joey, and a few others I have known for more than 20 years.

It’s hard to compare the weight profiles from different aftermarket manufacturers. Below I will give you the exact set up that I am using. Is it perfect? No. But after nine different clutch set ups I believe it is working very well for my needs.

I have the same 1 3/4” Backcountry X track. (I have a 141”) My 22/48 gearing is about 5% lower than yours. I have a stock airbox but I have a Straightline performance header and exhaust can. I have the Black Diamond (SSI) “Four stroke weights”. This is a heavy flat curvature magnetic adjustable weight. They are very inexpensive at only $150. Two magnets in the heel and three magnets and the tip. Nothing in either of the center holes. (With a stock engine I would start with less weight in the tip.) I’m using a Yamaha pink green pink spring. The Yamaha green green green spring is very similar with the only difference being about 100 RPM less on the top end. My engagement is about 2900 RPM and is very smooth.

My driven uses the stock pink spring with a 3/3 wrap. I have a Shockwave adjustable helix approximately set at 46/38. An 8 degree differential may be too much. I would recommend 44/38 or 43/37. My driven clutch was machined by Ulmer Racing for overdrive and for using the 8dn belt. Ulmer is a website sponsor.

This setup pulls hard down low at about 8600 rpm taking advantage of the 4 stroke torque and it builds rpm through the shift curve. Top end rpm is about 9050 depending on conditions. The lower rpm early in the shift curve is a trade off I made for better gas mileage at the expense of a little bit of midrange pep. Less initial helix angle would raise the low speed rpm and straighten the shift curve. Again, Black Diamond will custom cut clutch cams for a very reasonable price. I would love to recommend a supporting vendor of this website but I am not aware of anyone else that has such competitive prices.

 

[agetnt9]

You da Man !~! Can't thank you enough. I don't know what gearing i have as it was a test sled in Montana and Wyoming. (600 Miles on it) . It is a 16 MTX but set up like a BTX like a 17 i think . Got it cheap! I will put a little weight in the tip and go from 60 to 50 % and see how that works out.
If that don't make me a happy camper i will see what the gears are and go from there. I will try the ssi weights later on. Oh, the shifting down is not a 4 stroke thing. It is like a car automatic trany, when you are going from drive to 3rd gear at about 45 mile an hour,, it slows you down. You can feel it shift. Something is not right with that. I will figure it out one way or another. And Share it. Thanx again.