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Old 04-09-2019, 05:27 AM
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Default New build with Predator 420cc w/ 40 series

Hey all.

Just got my kart running yesterday.

I'm not sure I have the converter installed correctly. At idle the thing wants to take off! It seems like the idle is OK, but the belt isn't really slipping on the (driver?) pulley and starts squeaking if I keep it from moving. Shouldn't the belt be slipping easily at idle? I think I may have the driver pulley installed backwards because everywhere I look shows it installed the opposite BMI karts specifies....

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Old 04-09-2019, 08:16 AM
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Uh, your driver pulley is on backwards. And i think that your driven may have the wrong spring.

Other than that, nice kart.
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Old 04-09-2019, 09:13 AM
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Quote:
Originally Posted by J.S.@SMS View Post
Uh, your driver pulley is on backwards. And i think that your driven may have the wrong spring.

Other than that, nice kart.
Ok thats what I thought! Thanks I'll try swapping it when I get home.

As far as the spring goes, not sure. That is what changes the RPM at which it engages right?
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Old 04-09-2019, 12:23 PM
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The driven spring sets the shifting/opening rpm, and determines the orientation, outboard or inboard. It's the driver springs and weights that control the engagement rpm.
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Old 04-09-2019, 02:13 PM
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Isn’t the backplate in backwards???
Are there gussets on both sides (where the jackshaft bearings are)?
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Old 04-09-2019, 02:40 PM
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Good catch, I didn't even catch that. And there is something fishy about that spring. It looks like it's reverse wound.
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Old 04-09-2019, 06:11 PM
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Yes, like mentioned the plate is on backwards and the front pulley is also backwards.

I would also check to make sure your idle isn't set too high, which can cause the torque converter to engage too soon. And make sure you have the brass slip ring on as well, which is what allows the belt to slip.
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Old 04-10-2019, 01:23 AM
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I don’t recall if the 40 series uses the brass bushing. I don’t think it does.
I assume this was purchased as a kit and I hope the eBay seller includes the proper spring for an outboard mounted driven pulley. I’d start with flipping the backplate, flipping the driver unit, moving the axle sprocket to realign, and see how it works when installed properly.
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Old 04-10-2019, 01:32 AM
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Now I’m not sure the plate is backwards.
I had a heck of a time finding it being sold online.
And since talking about these, what really defines inboard or outboard when talking about driver or driven units on these TCs. On a regular Gokart centrifugal clutch, if the sprocket is on the engine side, the clutch is inboard. But what the determining factor with these units? Is it the movable sheave? Is it the stationary side?

I ask because BMI sells the same kit and it says the driver unit must be installed inboard on the crank. What does that even mean?
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Old 04-10-2019, 06:19 AM
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So I flipped the driver pulley around and moved the driven sprocket to the outside so the driven pulley could be lined up correctly with the drive. Is it OK that the drive sprocket is on the outside? It seems like it puts alot more load on the jackshaft being outboard. Might be able to put it on the other side of the back plate...

Buttt...it seems to be working correctly. It wants a to move a little but not nearly as much as before. I can easily hold it with the brake. I tried to adjust the idle but I couldn't get it lower then how it came.

Yes the kit came from BMI, and that verbage about running it "inboard" confused me too. The picture on their site must be wrong. I basically followed the comet instructions. There is also no way to mount the driven side with the springs inward as it would stick out too far away from the engine to ever be lined up with the drive.
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Old 04-10-2019, 07:12 AM
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If you mean that the sprocket is on the end of the jackshaft, I wouldn't run it that way. That's about the best way to bend or break a back plate. I learned that the hard way.

I checked on the listing at BMI karts, and it shows a picture where the driver is installed the same way that you had it originally. So it might be the kit. I really haven't seen one like it before.
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Old 04-10-2019, 07:14 AM
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Quote:
Originally Posted by J.S.@SMS View Post
If you mean that the sprocket is on the end of the jackshaft, I wouldn't run it that way. That's about the best way to bend or break a back plate. I learned that the hard way.
Ok thats what I thought. It just seems wrong...


Quote:
I checked on the listing at BMI karts, and it shows a picture where the driver is installed the same way that you had it originally. So it might be the kit. I really haven't seen one like it before.
Gopowersports sells a 40 series kit too and it shows it like this:



I'll try flipping again for the sake of the sprocket/moment arm issue.
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Old 04-10-2019, 07:27 AM
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Sorry, I meant to put this up on the lase post. This is the picture of BMI's kit as installed.
Click image for larger version

Name:	bmi 40s.jpg
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ID:	106537
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Old 04-10-2019, 07:47 AM
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Quote:
Originally Posted by J.S.@SMS View Post
Sorry, I meant to put this up on the lase post. This is the picture of BMI's kit as installed.
Attachment 106537
Yep thats what I referenced on my first install. The way I understand how it works is the centrifugal force causes the sheaves to move inward so it shouldnt matter which way its rotating.

I've got my brakes worked out now so I will repeat and retest.
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Old 04-10-2019, 10:48 PM
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Maybe your idle is too high or the linkage is binding up or your throttle cable is too short. ???
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Old 04-11-2019, 04:56 AM
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Got it hooked up the way the picture shows, no problems. Ran it for about 30 minutes yesterday hauling the wife and kid around



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Old 04-11-2019, 12:03 PM
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Next step:
Add performance mods(the crazier the better) so that you can have the kart to yourself, since the wife and daughter will be TERRIFIED by the speed and noise!
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Old 04-11-2019, 12:37 PM
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Actually, the next step needs to be seat belts. And not the lap belts that it looks like you have, I mean lap and shoulder belts. And if you upgrade the exhaust, use a motorcycle muffler.
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Old 04-11-2019, 02:30 PM
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Quote:
Originally Posted by LightningTeg View Post
Got it hooked up the way the picture shows, no problems. Ran it for about 30 minutes yesterday hauling the wife and kid around



This is really interesting. I am well versed in snowmobile CVT's but was very confused following these cart forums.

The usual rule of thumb with these symmetrical systems is that the two pulley fixed sheaves should be on opposite sides of the belt. With your picture, during upshifting the belt moves to the left as it walks up the drive pulley fixed sheave and also to the left as it walks down the driven pulley fixed sheave. Your setup makes sense.

In these forum posts the drive pulley always has the fixed sheave inboard and people are switching the driven around to fit, at the expense of proper belt alignment. I found a Utube video in the past where someone experimented with the orientation that you have and they claimed it worked good.

Your right in that the drive pulley is bi-directional. The driven requires a specific direction of rotation using the right side ramps and spring wind. I believe that yours is good.
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Old 04-12-2019, 12:38 PM
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Quote:
Originally Posted by JTSpeedDemon View Post
Next step:
Add performance mods(the crazier the better) so that you can have the kart to yourself, since the wife and daughter will be TERRIFIED by the speed and noise!
lol My wife is already afraid to go even 30%. I thrashed it pretty good yesterday it was awesome.

Quote:
Originally Posted by J.S.@SMS View Post
Actually, the next step needs to be seat belts. And not the lap belts that it looks like you have, I mean lap and shoulder belts. And if you upgrade the exhaust, use a motorcycle muffler.
I actually have no belts in right now, but I have belts out of the car the seats came from which are lap/shoulder and will work with the buckles on the seats.

Quote:
Originally Posted by Snaker View Post
This is really interesting. I am well versed in snowmobile CVT's but was very confused following these cart forums.

The usual rule of thumb with these symmetrical systems is that the two pulley fixed sheaves should be on opposite sides of the belt. With your picture, during upshifting the belt moves to the left as it walks up the drive pulley fixed sheave and also to the left as it walks down the driven pulley fixed sheave. Your setup makes sense.

In these forum posts the drive pulley always has the fixed sheave inboard and people are switching the driven around to fit, at the expense of proper belt alignment. I found a Utube video in the past where someone experimented with the orientation that you have and they claimed it worked good.

Your right in that the drive pulley is bi-directional. The driven requires a specific direction of rotation using the right side ramps and spring wind. I believe that yours is good.


Heres a video

https://youtu.be/uO9LtIXhG8w
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