clutch help

[o4twinpeaks]

working on setting up the clutch. 70cc holt pipe and porting yamizooto var and shoe pack koso 1500 black torque spring koso 2000 shoe springs 4.5 koso rollers 1 shim in var

with the cover off im getting about 1/4" belt travel before the clutch locks up. 3.5 rollers and this thing revs to the moon and will barely come out of the hole. 4 are better but 4.5 was the best at coming out of the hole but still a little slugish. where do I go from here? Heaver rollers engage soon but the lighter ones rev to high.

Tom
410 808 4658

[greenmachine70]

try 4.25

[o4twinpeaks]

Ok I switched to the red malos spring and with the 4.5 it engaged about 1/2 way up front var. went to 4.25 and it got a little better. Seemed to come out of the hole with him on it but we are out of day light now.

Now why can't I get this thing to come out of the hole with the koso spring? From my understanding the red is lighter than the koso. Last time at the track with the red spring it seemed like it need more rpm so up top so thats why I'm playing with the koso now.

[o4twinpeaks]

Originally posted by greenmachine70
try 4.25


lol i was typing as you were posting lol

[EthansDad]

First off, its not a good idea to run the bike up to full rpms with the CVT case off. notice that bearing inside the CVT cover? it there for a reason. you might find yourself testing a minor setup issue, and left with a major case failure.

for why its not launching, my guess is that its shifting BEFORE the bike starts rolling/rear wheel start moving (clutch stall or engagement).

keep in mind, its a balancing act between the rollers and the rear spring. the rollers do ALL the work, the spring just provides resistance against the work. the clutch shoe springs just change the stall, or can help fine tune the balancing act between the roller weights and the rear T-spring.

Also, full variator belt travel is highly over rated. I can tell you on all of our MX race quads, we don't get full travel, and it does not hurt us. if you are racing flat track, that might be a different story.

What I'd check on the setup is this. take the CVT cover off, put the bike on the stand and see if the belt starts rising BEFORE the wheels start spinning. if it is, that means you are taking on in like 2nd gear and getting a bad launch.

to fix that, a couple things you can do. if you lower your roller weights like someone suggested, that will help, but might not give you enough belt travel. you could lower you rollers enough to get proper launch (wheels start moving BEFORE any up/down belt movement) and then lower your spring rate to allow for more full belt travel.

in other words, you can not just move from 4.5 to 3.5 rollers without (possibly) having to switch how stiff your rear spring is.

for the clutch shoe springs, you can change stall speed that might help a bit. so if your belt starts moving before wheel travel, if you use a lower weight clutch shoe spring, you start the wheels moving sooner. the down side there on a 70 (depending on how well built the motor is) is that you might not have enough power at that RPM to get the best launch possible, even if starting at 1st gear.

clear as mud?

if you have a stock, or mildly built 70, 4.25 rollers with a 1500 ZTR spring and 2k clutch shoe springs on a 782 belt is a pretty good starting place to fine tune from.

-EA

[thequadfather+2]

Originally posted by o4twinpeaks
working on setting up the clutch. 70cc holt pipe and porting yamizooto var and shoe pack koso 1500 black torque spring koso 2000 shoe springs 4.5 koso rollers 1 shim in var

with the cover off im getting about 1/4" belt travel before the clutch locks up. 3.5 rollers and this thing revs to the moon and will barely come out of the hole. 4 are better but 4.5 was the best at coming out of the hole but still a little slugish. where do I go from here? Heaver rollers engage soon but the lighter ones rev to high.

Tom
410 808 4658

Our 70 has a stage 6 sport pro cylinder and a PCS pipe. We are running 3.5 rollers and a 1500 ZTR spring, stage 6 adjustable clutch with the orange shoe springs.....It launches fine and has good speed up top.

[o4twinpeaks]

Originally posted by EthansDad
First off, its not a good idea to run the bike up to full rpms with the CVT case off. notice that bearing inside the CVT cover? it there for a reason. you might find yourself testing a minor setup issue, and left with a major case failure.

for why its not launching, my guess is that its shifting BEFORE the bike starts rolling/rear wheel start moving (clutch stall or engagement).

keep in mind, its a balancing act between the rollers and the rear spring. the rollers do ALL the work, the spring just provides resistance against the work. the clutch shoe springs just change the stall, or can help fine tune the balancing act between the roller weights and the rear T-spring.

Also, full variator belt travel is highly over rated. I can tell you on all of our MX race quads, we don't get full travel, and it does not hurt us. if you are racing flat track, that might be a different story.

What I'd check on the setup is this. take the CVT cover off, put the bike on the stand and see if the belt starts rising BEFORE the wheels start spinning. if it is, that means you are taking on in like 2nd gear and getting a bad launch.

to fix that, a couple things you can do. if you lower your roller weights like someone suggested, that will help, but might not give you enough belt travel. you could lower you rollers enough to get proper launch (wheels start moving BEFORE any up/down belt movement) and then lower your spring rate to allow for more full belt travel.

in other words, you can not just move from 4.5 to 3.5 rollers without (possibly) having to switch how stiff your rear spring is.

for the clutch shoe springs, you can change stall speed that might help a bit. so if your belt starts moving before wheel travel, if you use a lower weight clutch shoe spring, you start the wheels moving sooner. the down side there on a 70 (depending on how well built the motor is) is that you might not have enough power at that RPM to get the best launch possible, even if starting at 1st gear.

clear as mud?

if you have a stock, or mildly built 70, 4.25 rollers with a 1500 ZTR spring and 2k clutch shoe springs on a 782 belt is a pretty good starting place to fine tune from.

-EA


Yes I was only checking engagement with the cover off. We are only doing 300' dirt drags so we are looking to get full travel out of it. Even with the 4.25 the belt is still climbing on the var before the rear clutch hits. I see what you mean about changing the springs to lower the engagement. I wasn't thinking about that. Billy did a mild port job on it for us and set it up to run with his "snake pipe" the one that you don't have to remove the battery to install. We are still using the 780 belt for now.

What the advantage of going to the 782 belt?


" the clutch shoe springs just change the stall, or can help fine tune the balancing act between the roller weights and the rear T-spring. "

Am I misunderstanding you? I thought the only thing the clutch springs did was control when the shoes hit the bell. Yes with light springs I believe it would hit before the pipe. I will try some 1500 springs next time we get out.


Thanks
Tom

[Logan #34's Dad]

You may just need a longer belt. Try the 787 belt. Just fyi, the first number on the belt, i.e. 787x16.5x30, is the length in mm. USUALLY. Some off brands are measured using a different measuring system. And for future reference: the 16.5 is the width, 30 is the angle of the "v".
My first listed sponsor can get you the 787 belt.:p

[nastynotchback1]

is the pipe made to be bottom end friendly???

[o4twinpeaks]

from what I understand from billy its more of a mid range pipe than top end. I asked him to port the cyl to work with his pipe. he never really talked about bottom end. I should have asked but I haven been able to get a hold of him since dec and no calls have been returned.:(

[nastynotchback1]

From my experience most pipes made small enough to fit with a batt will not have very good bottom end power.

[o4twinpeaks]

Ok I will remember that. These little engines are just so finicky on tuning. I'm used to tuning the 700 vtwin where you have the power to overcome poor clutch set up. lol It seems to be getting better and I'm headed in the right direction now. I Think

[nastynotchback1]

my set-up pulles the wheels off the gate with an a/c true 70cc motor.

[EthansDad]

so, in an ideal world, you'd know the power of your motor at the crank. pipes, porting, etc will give your motor a unique power curve, like I'm sure you've seen before on 2 strokes. looks like a bell curve that flattens off at the top.

just to put some numbers to this for conversation, let's say you looked at a crank side dyno of your motor and you saw that the curve STARTED to go non-linear at around 5k rpms, and peak power happened at 10k rpms, and it turned a max of 12k rpms

you'd want to have your stall at or around 5k rpm (no sooner or you bog the motor) and have the clutch set up to do ALL shifting at 10k rpms, with over rev to 11-12k or what ever the motor will turn to.

you'd also want at launch (stall rpms) to have the bike in first gear, then at 10k rpms start shifting up, maintaining the rpms at 10k through out the shift cycle. at max shift (call it 4th gear) then the bike over revs to 12k and might pick up some more speed.

anything less than that for our fictional motor would be less than ideal in the world of cvts.

for your point questions, a longer belt as others have noted will give you more ratio, and based on different width will change your stall a bit (thinner belt will grab later than a thicker belt). a 780 (being short ratio belt) will get through the shifting quicker, an on the other end of things, a 787 will give more launch and more top speed, but shift through things slower (more belt to travel). bikes either love or hate a 787, it is worth testing, but the 782 is a good mid ground choice.

on clutch shoe springs, you nailed it. the only thing they do is control when the shoes hit the bell, or start the wheels moving, often called stall. if you get into fine tuning, you might like having an adjustable rear clutch, like a stage 6 that offers much more tuneability (and easier to change) stall settings.

I've never setup for drag racing, but I'd guess the ideal settings are to launch good, and reach the max top speed possible (based on given HP of the motor). I might try a long belt, like 787, some very heavy rollers (to make sure I get full shift), over come pre-shift with different variators (or shims) to get it matched up. the rear spring really is the last variable with ideal setup. I just need enough resistance to the work to balance the rest of the setup in a rear spring.

and not to throw some mud, but quadfather, didn't our stock 50 stick with your full mod 70 on the hills at mill creek? I know we did not have more power. its all in the clutch!

-EA