The CVT seems pretty well in tune, as far as weights and the contra spring. That doesn't mean I can't still try to improve the way it feels and acts though. In particular, I had belt travel on my mind for this next mod. This first picture shows how much marker is left on the variator after running the scoot at it's max speed of 51MPH. 5.81mm is a good bit of variator being put to no use on the top end of the gearing.
This next image shows how close the two halves of the front pulley could potentially get, assuming the rest of the CVT tune and engine power allows it. Just shy of 16mm. If you are thinking, "but my belt is 17mm stock", you don't actually have to grab the whole belt when it's at full travel for max performance. On some of my other scoots I've had the outer edge of the belt beyond the outer edge of the variator. Also, in reality most 17mm belts are shy of that be 0.5mm or more sometimes when new. After the belt is worn it can easily get to 15mm, less if you allow it. For these, you should be replacing the belt around 15mm however.
The other side of gearing is your "first gear", or the initial position of the belt that gets you off the line. The easiest way I know of to show you where the belt is at that point is to show you how far up it rides in the rear pulley. Showing how far down the belt travels in the front would be nice, but it's harder to get a picture of. Here's the belt in the rear pulley with everything stock. I've seen worse, but there is definitely room for improvement.
Here's a look at the front pulley in stock form, all the way open.
My first plan of attack involves this little lip built into the variator fan, or fixed half of the variator. As you can see it's roughly 1mm deep.
My thought is that by removing this lip the front pulley can not only open wider, but also close roughly 1mm tighter than before. In theory, that should allow for the belt to ride lower in the front pulley and therefor higher in the rear pulley for an improved "first gear". One would also think that closing the front pulley a little more should allow the belt to ride farther out in it's max "high gear" to increase potential for top speed.
The lip can be easily filed off and then sanded to remove deep gouges if you use very rough files. You could also use sandpaper and glass (
as described here) to accomplish the same thing. A lathe, a belt sander, there are all sorts of ways to do it. Just be sure to keep it even so your pulley isn't lopsided. I cheated and used another stock fixed half that I had done in the past... kinda like how the TV chefs pull a dish already cooked from the oven. ;D
Here's a shot of the pulley all the way open after filing the lip off. A little more room now for the belt to start off lower, closer to the drive boss.
Once it was all installed, you can see that the belt is riding higher in the rear pulley.
This image shows that the front pulley will close roughly 1mm more than before for it's max top gear. From 16mm initially, to 15mm now.
Here's a video of the first test pass. Initial launch is slightly improved. It seemed to be struggling a little more with the speed above 43-44 though.
The leftover marker now shows 6.6mm of unused space on the front pulley, more than before, but I was not that concerned. For max speed and belt travel, I usually tuck down as far as I can and give the scooter plenty of time to stretch it's legs on flat ground. During the day, when there's usually no one else around to watch my grandmother, I won't go very far at all on a test pass so if I do breakdown I can get back fairly quickly pushing the scooter. I generally get out at night when there's no traffic and no time limit to stretch it out as much as it will go.
Even without any increase in top speed yet, I still felt like I was on the right track and I did see some improvement in acceleration from a stop. The fixed half is not the only part of the front pulley with a little excess material that can keep the belt from getting all the way down in the front pulley or from closing as tight as possible. As you can see here, the movable half has roughly 2mm of aluminum protruding past the brass guide for the drive boss.
I began by filing the center down.
Before filing and periodically during filing, I kept check on the ramp plate and guides on the rear of the variator. You can sit the variator face down on a flat surface. Then put the drive boss in place and sit the ramp plate on top of that. You want to make sure that you don't file so much of the variator's face away that the ramp plate will clear the guides. Try to leave a little extra room, not just right on the edge, to be safe. If the variator and ramp plate separate so much that they are able to move freely from one another, they may not line back up on deceleration easily or at all. I've done this before and ended up with variators that constantly break the plastic guides on the ramp plate and damage rollers and at times even stuck in high gear.
I went a little farther than just filing the face flat. When the center of the face is flattened out, sometimes you end up with an odd spot in early acceleration. Flat filing creates a very abrupt transition from flat to angled surfaces. I sanded and filed to smooth out that transition better so there's less of an obvious ridge on the face.
I left a bit of a lip, but not much. As I noted earlier, trying to stay on the safe side and keep the vari and ramp plate in line with each other.
While I was at it, I opted to smooth out the transition on the fixed half as well.
You can see there is even more room for the belt to get low in the front pulley.
This is even more clearly demonstrated by how far out the belt can ride now in the rear pulley.
Now the two halves can close up within a bit over 14mm of each other.
With the variator marked again, I went for a second quick test pass. The video didn't turn out so great, but you aren't missing much vs the first one here. Takeoff was improved slightly more. Top speed was 48MPH this time. Upon disassembly, I found that I had still less belt travel than last time, even though I was going a little over 1MPH faster. Seems a little counterintuitive, but that's the result.
Once I could get out for a few minutes more, I took a very brief ride so I could try full tuck for a slightly longer distance. Once again, I saw the 51MPH top speed that I'm getting very accustomed to. Max RPM showed 8,800.
Belt travel increased a bit from my shorter run, but it's still a little over 1mm less travel that I got before modding.
When I took the last ride, I placed the GPS and the GoPro under the seat together. I thought maybe I could get a video of the GPS recording the speed to show you, and I for that matter (can't see my speedometer at night), how it was doing. Seemed like a good idea, but the video turned out to be horrible. The camera was moving all over the place, probably because I hung it from that "rubber band" that attaches to the bottom side of the seat so it bounced and such. Definitely not good enough that I wanted to post it. It did at least allow me to see, in a bouncy blur, my speeds creeping up. It's not terrible, but it has lost a little acceleration from about 45MPH to max.
To sum this modding segment up, if you go back and look at the pics of the belt in the rear pulley at start and finish, you can clearly see that I made an improvement in the "first gear" ratio for the better. The more free feeling caused by the belt not binding as much at a stop or on launch also makes it feel a little better to pilot. You can also see that I clearly have made the front pulley's potential for closing greater, however I have not recognized this potential. In fact, I have made the actual belt travel less in top gear. Even given that, I managed to retain the exact same top speed. The only unfortunate part being that the last few MPH are a little harder to come by. For real world riding, most people won't be full tuck for very long, so I feel this to be only a minor setback.
Even though the results don't show any great progress, I do feel like this mod is a good one. I have done this same type of mod, mostly on aftermarket variators however, in the past with much better results. I believe the reason I have not seen really positive results on the top end in comparison to past endeavors is the difference in engine power of this project and final drive gearing vs the others I have tried. I generally have started off by getting the engine tuned where I want it, and then moving on to fine tuning the CVT. For my own projects, I know where I want to be and I take the fastest path there. In this project I am trying to take some steps as I feel others may and wanted to try this early on because it is a free mod assuming you have a file and some sandpaper.
My theory is that the scooter in stock form simply doesn't have the power to pull these gears with my weight significantly faster on flat ground. I do believe it's possible to go faster with the stock horsepower and gearing, but not by a great margin. The potential is there to go faster based on what we've seen here. One bright point is that I did the same top speed with 1mm less of belt travel. The CVT is operating in the proper RPM range for the stock engine. I think those facts support my thoughts.
