Sym Mio 50 4T weird cdi ? By rob63 (Read 9,393 times)

[rob63]

Hi all, I have a problem at work with a Sym Mio 50, the fault is intermittent and will sometimes run fine then suddenly run rough with an inability to rev up. At first I looked at fuel problems but to no avail. I eventually got to the cdi and whilst touching the terminals the bike would come back to normal then go back to rough. Today I lost all spark completely. When I looked closely at the cdi I noticed it has a different pin arrangement and an extra wire.
Here`s a normal AC cdi....


And here`s the Sym cdi....


As you can see most of the pins/colours are the same and seem to perform their standard duties except the two left wires. The blue/yellow is still the trigger wire but is now on the Green/ground (2) pin, and at the top where the blue/yellow normally sits there is a plain black wire which is a 12v feed from the ignition switch.

Does anyone know why there is a DC feed to an AC cdi unit. Sym has a habit of fiddling with their parts so that aftermarket parts won`t fit so I put the different pin positions down to that, but the black wire has me stumped.

If this cdi is duff then I`m wondering if I can fit a normal cdi in it place by moving the blue/yellow wire back to it`s standard position and ditching the black 12v feed.

Any thoughts please ?

[Bashan]

Here is your wiring diagram from the manuals section in our Library:

I have some thoughts, you are indeed correct, that wiring configuration is nothing like a standard GY6. You need to find a SYM CDI for your bike and swap it out. Trying to wire in a GY6 CDI would require massive reconstruction. The black is a power feed and that usually runs to the two port, not the four. But there is a power feed to the two port also. The trigger comes from the engine start control module which I have no idea what that is. I have a SYM and luckily it is bullet proof and I haven't had to do anything other than change the fluids and set the valves. I would not want to tackle the wiring on my bike especially with EFI, but I would if I had to. But you should find a SYM dealer and buy a new CDI and plug it in. Rich

[Alleyoop]

Get the number on the back side of that CDI.
Alleyoop

[Bashan]

Oh Rob, I'm sorry, I didn't see it was you. Yeah mate, that thing is a nightmare. But you work on them all the time don't you? Maybe you know what that module is. I just think it would be better to get a OEM replacement, that schematic looks like trouble to me. Rich

[cyborg]

So you touched the terminals while running ,, it got better then went bad again and now nothing?,, termination of connectors ok? Wire broken internally?

[cyborg]

Push the wires into the terminal blocks then try it again,, I've had more than one bike give me grief from termination problems

[rob63]

Thanks for the replies lads.
Bashan, the module is a sliding switch which is simple anti theft device, we have a little plug which bypasses it to test the circuits.
Cyborg, I`ve checked the wires and terminals and get good continuity so I think that side is good as far as I can tell.
I did wonder if it was an internal problem with the cdi from the start, as the black 12v feed wire showed positive when ignition on, but when the scoot started running rough the black wire had a positive/negative pulse on it which would then change back to a positive when the scoot sorted itself. A possible short inside the cdi ?
I`m now wondering if the black wire controls some sort of ignition advance circuit inside the cdi, if faulty it would explain the inability for the engine to rev up ?
Alley I`ll try and get the numbers off it

[rob63]

I had a brief look at this one today and got a number off the cdi. Sutai A1A-CDI, A1A-9100, K20Z3.
I noticed that the kill wire when plugged in to the cdi has an earth even with ignition off. If I unplug the 2 pin plug then the kill wire works as normal ie: earth with ignition off and no reading with ignition on. Which makes me think that there is a short inside the cdi.

[rob63]

Popped a new cdi unit on today, bike started first time, left it running for half an hour and no problems.
Normally the cdi units I`ve come across have failed completely, no hiccups or odd running. I can only think that this one had a dodgy earth short to the kill wire which gave a weak spark now and then.

[Bashan]

Thanks for the update, it may help another SYM owner in the future. I just like hearing cool words like dodgy and earth. It makes me wish we never came across the pond. It'd be kinda crowded over there wouldn't it Rob?

[rob63]

Yes it would buddy, only a small island

[axa]

adding to this helpful info, I've confirmed you just need to pinch out the 12v switched wire, pop out the trigger wire and pop it in to where the 12v switched wire was and all is well.

I was going nuts never figured SYM would use some proprietary, seeming needless, CDI when any cheap AC CDI of eBay will suffice.

bonus. you can then use the left over key switched power line to hook up a regulated USB port as I did.

[kurtbeine]

Hi guys, new here, trying to fix a 50cc Fiddle, bike runs, but low on power, won't go over 20 kmh. I sourced an aftermarket CDI on Amazon, scooter won't even start with the replacement. Everything says to me the CDI is a problem, but it seems aftermarket units don't always work the same, are there any wiring diagrams I could see?
Based in Germany.

[kz1000st]

Have you checked for vacuum leaks in the intake or emissions system. Also that the exhaust pipe is clear and not dented. YOur issues sound more air and gas flow problems than electric.

[kurtbeine]

Yes, I've heard of the exhaust being a possible problem, I will check that shortly, easy to just unbolt it and give it a go....wrapped up with Corona at the moment, quarantined for a few days....