Author Topic: My experience tuning up a mio 50  (Read 843 times)

axa

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My experience tuning up a mio 50
« on: April 06, 2016, 01:41:43 AM »
So I picked up this little bike last fall for my gal, off some old lady who said it scared the shit out of her.  Didn't know what that meant at the time but I realize it has a bit of delay on take off as the variator hesitates to close.
I'll be trying some new roller weights but that's a story for another day.

When I picked it up on that chilly day it wouldn't start. It had been sitting for years, only had 63 miles on the odometer, never had a problem i couldn't fix so she liking scratch free, coffee white bike so much, we loaded it and went home.

Ultimately I had a hell of a time getting the bike to run.  A carbed bike is an ingenious yet simple machine, but you have to be meticulous debugging unknown issue(s), even more so if it's a unknown bike, in unknown condition. Cuz when you have multiple issues like I had, it can be maddening.

what i think makes little scoots, and this one in particular, a bit more tedious to work onis the entire intake system.  It's ridiculous. 
Imo it's responsible for way too much which is the reason there are a dozen passages with a dozen hoses and it's real easy to get confused and not so hard for a problem in one system to possibly effect another.

Firstly there are too many things relying on the vacuum.  Including the important carb slide. There has to be enough vacuum to suck the slide diaphragm up.
Some say the smooth transition of a vaccum carb is superior, but I like to have control of my slide with a good ole cable, that eliminates questions with weak vacuum.

Secondly the fuel petcock relies on the vacuum.  here too I prefer good ole gravity for the same reason as above.

But third, theres the EPA mandated secondary air system also relying on that vacuum, which I have no alternative for except to ditch the entire intake system.

I could find no leaks but didn't get enough vacuum to raise the slide.
Removing the entire intake simplifies the system, raises the vacuum and allowed me to find the second problem.

The only way I was able to idle was having the idel set so high it was bypassing the pilot system entirely.
This bike comes with one of the smallest pilot jets available 35, and sitting for so long it easily clogged as it had.
Only I pulled it out and washed it twice, but the hole is so small it's hard to be sure it's clear or not.

An oversized pilot will do for now but I have a set 35 to 50 on the way from flea bay.
My stock 88 main jet is doing OK but I havnt done much WOT yet.

The moral of this story is concider ditching the useless intake and capping the carb off with anything that keeps the critters out.

You'll likely need to rejet but I'll report back with final replacement jet sizes when my kits arrive and it's been dialed in.

PS my bike came with the variator ring restriction, and as far as I know that is the only restriction.

That bean bag thing is NOT a restriction but part of the emmision controls, specifically a charcole activated filter at the end of the gas tank vent
Basically a vent hole on the top of the tank connected by tube which merely collects any fumes a tank might squeeze out on a hot day or when the tank is over filled.

I never rode while it was restricted but just without that ring it fast enough to frighten me with such a short ( unstable ) wheel base.
 I like to ride fast, but i don't like it on this bike.

More to come.

axa

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Re: My experience tuning up a mio 50
« Reply #1 on: April 18, 2016, 01:39:40 PM »
so after pulling the entire intake off, and with a new set of pilot and main jets... Ive oddly found that the stock 35 pilot is best regardless..
This is not shocking but was surprised how rich the next larger 38 size was with no intake to speak of...

and in light of not changing too many things at a time, im leaving the stock main at 88 as i havnt yet seen problem and havnt done much WOT riding

So if your having starting problems like i was, looking to simplify your system by removing the intake, then at least there is some evidence that you dont need to rejet.


That said ive narrowed down my hesitation on start with the clutch engagement. seems that it takes too high a rev/rmps to get it to grab.

Anyone have any idea what the stock spring rating is?
1000, 1500 2000?

No, of course not, on this forum i feel like im talking to myself.
im just figure id put my thoughts up for others...
« Last Edit: April 18, 2016, 01:42:53 PM by axa »

bltkmt

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Re: My experience tuning up a mio 50
« Reply #2 on: May 06, 2016, 08:14:10 AM »
No, of course not, on this forum i feel like im talking to myself.
im just figure id put my thoughts up for others...


 ;D  Exactly.  I wish these forums were more active.  Not enough of these Mio 50's out there I guess.

axa

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Re: My experience tuning up a mio 50
« Reply #3 on: May 27, 2016, 05:57:38 AM »
so this scoot seems to be starting, running nice.
After complaining about a hesitated take off, I just swapped out the stock springs to a set of 1000rpm springs.  Regardless of the color, I found you can just observe the wire gauge of the springs to indicate the performance.  Still dont know what the stock are but they are noticeably thicker. And as estimated the take off is now adequate.  Ive found no reason to touch the rollers or contra spring.

Finally got the thing plated and insured, here in NY, there are 3 classes, the B class up to 48mph require those.
Quite honestly i could have registered it as any class but the B was not only technically correct, but it allows my gal to ride without getting an M class license, and not needing annual inspection.
The C class would have been a tad bit cheaper to register and didn't need insurance but as she can afford insurance otherwise, I thought having some coverage was a good idea anyway.  one year 50$ including 10K in medical for the record, which is exactly what i pay for my bobber so go figure...

That said we took it for a cruise to pick up the 2003 vw bug we just bought, and with the both of us it had a top speed of exactly 39mph on a flat.
She told me alone on the way back she rode 40 with some throttle left over but just as I felt the thing is just way too unstable to push faster.  It has such a small rake and trail that it tends to easily be nudged in any direction, so riding any faster is just scary.  Therefore I wont be looking to mod anything further.

So there you have it, in summary my experience reviving/tuning a little used mio 50:

-removing all the intake simplifies the system and allows you to find/fix problems more easily.  Specifically it strengthens the vacuum which i found important with the VM carb.  And I didn't even find need to re-jet replacing the clogged stock 35 pilot jet with another 35.

- I found a 1K set of clutch springs required to get rid of the hesitated take off.

- The valves are way hard to get at, I'm ashamed to say I didn't even check mine.  But every Chinese bike Ive had so far has required adjustment so...

Now if someone can tell me where to find a battery cover and floor mat!?

daveatkin65

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Re: My experience tuning up a mio 50
« Reply #4 on: July 30, 2016, 12:10:08 PM »
Hi AXA

If you email your address can send you a pdf of the mio 50 service manual and will give plenty of information for your bike. Recently got one myself free from my neighbour been lying around in his garden for the past year. Like you stripped down and found carb blocked with debris. Cleaned all out with petrol and can of compressed air all good. You can and should remove the ring on the actuator pulley at the front this will although your bike to rev more along with a derestricted cdi unit. Also as you have done adjusting the springs and rollers will also help not done myself yet.
look forward to your response
dave