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Clutching on the cheap

Why does it seem like there is such a large gap in RPM from low to a high load situation? 2 weeks ago I went to the mountains with a NA 15 viper MTX with stock clutching that would hit 9250 rpm on trails but when climing small hills with almost 3 ft of powder only got 7800 rpm. This weekend i have 8FP weights with the soft start clutch spring , 5 shims stock secondary set at 6-2. Testing on the powerline would hit 9250. Added solder to tip and got base weight to exactly 70 grams . put 4.5 rivit in tips. still hit rev limiter but will see how it does in mountains. If RPMs are low on a climb can I change secondary wrap in the hills?. This is my first 4 stroke and never had these issues on my summits. Rasing rev limiter would seem to be the best way to go to have a cushion, any thoughts. Thanks Fred
 

NOS-PRO said:
Going to post this because I am truly flabbergassed by aquaticlaker's sled and the power it is making stock with the COTC setup. I am poting this because this is the first sled I have worked on that is taking way more weight than I have ever put in a COTC setup for anyone!

I have him loaded with 4.5 in the tip and 3.0 in the middle with the 8FP's and he is still hitting the rev limiter hard. Now it's time to take it to the limit and really throw some weight at it!

I pm'ed Mike and told him to find some lead rivets or regular rivets (6-7 gram) or M6 x 1 screws/bolts & nuts....But we have to be careful and not go past the 1/8" maximum height on each side of the weight.
Click to expand...


I added 6 grams to the tip using a M6 x 1 and Loctite, Red. Checked the 8FP clearance and that was good!
Checked the height of the belt in the primary and that was 1/4 inch below the top roughly.

Went for short ride on the lake and did not hit the limiter. Not enough distance to keep going to check top speed and too icy! 89 was top. I can try it better this weekend.

Looks like clutch engagement is about 3000 rpm's. Top RPM's were 8900 but need more testing!

Mike
 
aquaticlaker said:
I added 6 grams to the tip using a M6 x 1 and Loctite, Red. Checked the 8FP clearance and that was good!
Checked the height of the belt in the primary and that was 1/4 inch below the top roughly.

Went for short ride on the lake and did not hit the limiter. Not enough distance to keep going to check top speed and too icy! 89 was top. I can try it better this weekend.

Looks like clutch engagement is about 3000 rpm's. Top RPM's were 8900 but need more testing!

Mike
Click to expand...

That is the most weight I have seen anybody use and I'm glad to see 8,900 instead of 9,280 ;)
 
Ok fellas, I went from the 3.6 g in the tip to a 4.5 because I was tapping rev limiter on long pulls, now across my field I'm only pulling 8600 (only about 500 ft at best). I thought it was only supposed to pull down rpm's about 200 per gram? Will test a little more tomorrow on the trail. Put my secondary back 6-1 (didn't like the 3-3) and have 3 mm of shims. Hope she all works out, was fun at first but now starting to get a little annoyed......
 
Hey Guys
Can Anyone tell me what the rev limiter is set at on the RTX? Running Ulmer Primary and Secondary clutch kit no turbo but it seems high at 9100ish! Only getting 94mph?
Thankx
 
fc8464 said:
Why does it seem like there is such a large gap in RPM from low to a high load situation? 2 weeks ago I went to the mountains with a NA 15 viper MTX with stock clutching that would hit 9250 rpm on trails but when climing small hills with almost 3 ft of powder only got 7800 rpm. This weekend i have 8FP weights with the soft start clutch spring , 5 shims stock secondary set at 6-2. Testing on the powerline would hit 9250. Added solder to tip and got base weight to exactly 70 grams . put 4.5 rivit in tips. still hit rev limiter but will see how it does in mountains. If RPMs are low on a climb can I change secondary wrap in the hills?. This is my first 4 stroke and never had these issues on my summits. Rasing rev limiter would seem to be the best way to go to have a cushion, any thoughts. Thanks Fred
Click to expand...

15 MTX comes with rather aggressive weights that force a quick upshift, the 8Fp do not. Let us know what you find after your test.
 
sparky72 said:
Ok fellas, I went from the 3.6 g in the tip to a 4.5 because I was tapping rev limiter on long pulls, now across my field I'm only pulling 8600 (only about 500 ft at best). I thought it was only supposed to pull down rpm's about 200 per gram? Will test a little more tomorrow on the trail. Put my secondary back 6-1 (didn't like the 3-3) and have 3 mm of shims. Hope she all works out, was fun at first but now starting to get a little annoyed......
Click to expand...

Yep 6-1 with more weight. Normally about 200 rpm per gram but that is just a guess/starting point. Check your weights and especially the outer primary sheave for binding also please.
 
So I finally got around to putting the COTC in my 15 LTX
8dn
4 mm shim
GWG
8fp with 4.5 in tip
And first nite out with a bunch of guys no formal races or anything but when ever we all took off it seemed my sled had the best hole shot and would just charge to 80-84 mph ,I am at 9000 rpm max,then just kinda creeps to 90mph ish.so yesterday I went out alone to do some top speed runs and found that 90 mph is all we could do ,which is about 7 mph slower then stock,the way it runs thru the low and mid range is just fine with me,it's a freaking animal ,really don't need more top speed ,but if there is a change I could make to get some back I will do it,have an mbrp can coming on Wednesday and will get the helix from Bruce as soon as he gets more in stock ,and I am assuming these will both help a little,thoughts from the guys in the know?
 
Had a great day of riding yesterday. Mostly blue skies 2 degrees above at the parking lot, warmed up to 15 during the day. Snow was 8 in. powder on top of 8 in. of a firm crust from last weeks rain and waist deep under that with no real base. First off the soft start spring is great, nice smooth take offs with no trenching which was perfect for the snow conditions. Take offs on full throttle on the valley trails where strong and pulled close to the 800's I was riding with ( 13 PRO RMK 155, 14 XM 154 and a 14 XM with a 146 ). On the climbs of the steep valley walls that was peppered with willows I could pull 7900 RPM and make close to 3/4 the way up going straight. I could then side hill and make it all the way on shallower spots. The 800's where climbing all the the way to the top if they could keep the nose down . Think if I could get my RPM's closer to 9000 with the heavier front end My viper 153 would have done real close the 2 smokes. Any sugestions on what to remove and would there be beifits to put weight in the middle? Thanks Fred
 
SISCAKIDD said:
So I finally got around to putting the COTC in my 15 LTX
8dn
4 mm shim
GWG
8fp with 4.5 in tip
And first nite out with a bunch of guys no formal races or anything but when ever we all took off it seemed my sled had the best hole shot and would just charge to 80-84 mph ,I am at 9000 rpm max,then just kinda creeps to 90mph ish.so yesterday I went out alone to do some top speed runs and found that 90 mph is all we could do ,which is about 7 mph slower then stock,the way it runs thru the low and mid range is just fine with me,it's a freaking animal ,really don't need more top speed ,but if there is a change I could make to get some back I will do it,have an mbrp can coming on Wednesday and will get the helix from Bruce as soon as he gets more in stock ,and I am assuming these will both help a little,thoughts from the guys in the know?
Click to expand...

Put secondary at 3-3 will take some mid away and put it on top. I have mine on 3-3 but miss the pull on acceleration from low speeds so putting it back to 6-1 although I think 3-3 is actually faster (but less fun).

You could also lighten the tip weight a little to get to 9150-9200 and that might get you a few more MPH back.
 
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