SYM Mio 50 tuning

[badmotorscooter]

Variator tuning, inconclusive? First of all the "performance" variator from Taiwan ($38) was not the right size. The stock boss diameter and length were good, but the overall diameter of the variator was only 88mm (stock is 108mm). So that was a no go for sure, but I didn't let that stop me from getting to work.

Shaved the variator boss about 1mm and swapped out the stock 6 gram rollers for some 4 gram. 0-20 was much better but after about 25 mph the rpm's started climbing above 8000 and the scooter topped out at about 31-32. 4 gram weights just couldn't push the variator out where it needed to be. Swapped in some 5 gram rollers and the 0-20 was almost as good (definitely peppier than the stock 6 gram) and the scooter maxed out at about 40 mph.

I might have actually lost about 1-2 mph on the top end, but acceleration is improved significantly. I recently reformatted my PC with a different version of Linux and had to download the SYM Mio 50 service manual again. I noticed this version said max horsepower was at 8000 rpm and peak torque at 6500 (the last manual said 7500? maybe for the Mio 100 instead?). That sounds more accurate for a 49cc engine. At 40 mph the revs are now 8600 instead of 8800+, but I noticed several other things. Cruising on level ground at 35 is right around 8000 rpm's, and going up a steep hill the scooter manages 30 mph or so and again the rpm's are at 8000. WOT from about 10 to 25 mph runs about 6200 - 7500 rpm's and then from 25 to 35 about 8000, finally climbing the last 600 to max out at 8600 rpm's at 40 mph.

So it seems that the variator tuning is very good for overall acceleration and the performance is better than stock unrestricted. I'm tempted to stop right here since everything feels peppy, and I'm not sure were to go from here if I still decide to try for a couple more mph on the top end. I think I might ride it like this for a few weeks and see how I like it, after all 40mph is respectable for a 4-stroke stock 49cc. If I decide to leave it be after that (yeah right!) I will simply replace the 5 gram rollers with 6 gram sliders.

[badmotorscooter]

I forgot to mention that belt marks on the variator showed 5mm unused on the outer pulley edge. Put the marker to it and
I will check again later.

[badmotorscooter]

The belt still didn't use the last 5mm of variator outer edge. Shaved the variator boss another 1mm (total 2mm) and put a 2mm washer behind the variator to keep everything aligned. Wow! The second millimeter made a much bigger difference and the scooter topped out about 37-38 mph at 7700 rpms running out of horsepower. Not to worry though, still had the 4 gram roller weights.

Right on the money, got it where I want it! Topped out at 41-42 mph with the rpm's at 8500. Got in a tuck and got 43 mph out of her twice. But the best thing is on level ground without a headwind it will cruise 35 mph at 7700 rpms's with some throttle left.
I would feel comfortable running the SYM MIo 50 like that for an extended period without worrying about stressing the little engine too much.

Overall acceleration feels about the same as the 5 gram weights with a 1mm longer boss. I'm hoping that less reciprocating weight in the variator along with the lower rpm's will net a small decrease in fuel consumption, which has been about 100 mpg so far.

I think this about wraps up my tuning, still gonna switch to 1 gram heavier slider weights as the last much longer than standard roller weights.

[Zino]

I would say you are close to dead on for your tuning that little bit of shimming added 2 mph .
That is alot of bang for the buck
Based on your tuning you like 4 grams just a notch better than 5 grams .
4.5 to 5 gram sliders would be the right ones .
I have found I can run just a notch higher sliders and get the same takeoff and pick up a little top end .
They do last longer .

[badmotorscooter]

Update:

Went on a 30 mile ride today with a mixture of all speeds. Without a headwind on level ground the Mio 50 will easily hold 40 mph consistently, I was impressed. On medium hill it will still hold 35 mph, steeper hills 30 mph. But I did notice one thing that was a bit of a compromise. With 4 gram roller weights and a drive boss shaved 2mm, when the clutch engages the gearing is definitely higher than stock. There is a wee bit of lag before the rpms rise and then it takes off with pep. Nothing critical, but noticeable for sure. I weigh 145 lbs, but I would imagine with a much heavier rider this would be a problem. The upside to this is much better throttle control at very low speeds, I can comfortably turn on a dime with little effort, making sidewalk, driveway, parking lot maneuvering amazing.

I have some 5 gram Dr. Pulley sliders on the way, wonder if that will help with the slight lag as the clutch first engages? Maybe some 4.5 gram sliders? If not I can try slightly stiffer clutch springs, just hope I can find some that don't raise the clutch engagement too high. But I can live with the slight lag if I have to, still very happy with the way the 4t 50cc performs.

[jbjhillbilly]

Nice work!

Seems like the SYM Mio tunes a lot like a Honda GET motor, which makes sense. 49cc 4-stroke motors only have so many differences.

4.5 sliders would seem to be just about right.

[badmotorscooter]

Update:

After failing to install stiffer clutch springs (see here: 49ccscoot.proboards.com/thread/27496/clutch-spring) I swapped out the 4 gram rollers for 5 gram Dr Pulley sliders. I had also went from 88 main jet (drilled out to 88.5 to 89) to a 90.

I am actually happy the stiffer clutch springs were not installed! The lag is gone, I guess the sliders fixed it? Now I still have very fine control between idle and partial throttle.

And today that low speed control was very important. Made a grocery run into town and got caught in the rain. It started as a light rain and turned into a gully washer! It was raining as I came out of the grocery store, so I loaded up the scooter and took shelter under a gas station in the same parking lot. I waited about 20 minutes until I thought the worst was over, and then took off. The streets were still pretty flooded and I did my best to avoid most of it. Back alleys, behind shopping centers, connecting parking lots, jumped a few curbs, and yes, the occasional sidewalk for a big shortcut. I avoided all main streets and most of the traffic so I didn't get soaked from cars spraying water all over me.

I expected the skinny stock tires to be slippery and treacherous and proceeded with caution. I was wrong! The stock Maxxis 90/90/10's were secure and confidence inspiring, I was able to tackle the questionable surface conditions without worry. When tire replacement time comes along I will definitely get another set. I was dodging deep puddles, potholes, rivers of water, speed bumps, washed up gravel and dirt and the like. I should have been miserable in the rain and somewhat stressed from the conditions? But I was having an absolute blast with a big $hit eating grin on my face! That sweet little 50cc scooter did what it was made for, few if any other two wheel vehicles could do it as well. At one point I ran through a pretty hard rain shower and just kept cruising at a steady 30 mph. Ducked behind the small windscreen, pulled my elbows and knees in and stayed mostly dry! My shoulders and a small part of my knees and thighs got wet, but the wind quickly dried these areas as soon as the rain relented.

What an awesome ride, it sure beats the normal heat! The scooter is pretty muddy, but I stayed mostly dry without getting muddy or dirty. The Sym Mio deserves a good cleaning and another coat of wax...

[soosh]

Love the Sym mio. Where are you getting all of your accessories from??