Out for ride the other day, after a lengthy stop, upon attempting to use the starter (not enough spin), I kick started the bike and upon leaving, within about 10-20 foot the bike died and I had experienced either a malfunction of the battery, or a poor ground off the battery terminal, or some other cause, that resulted in a burnt negative strap from the battery to the frame. Also found later that the fuse was blown.

I'm now concerned as to what has happened.

A very savvy motorcycle mechanic/electrical friend insists I need to check the condition of the "starter relay" before any further attempts with a new battery and new fuse. (FYI he is NOT conversant with the dynamao starter system on these Yamaha 125's and freely says so.)

I've been going over the schematic in the pdf file and I do NOT find a starter relay on this bike.

Any of you know these dynamo starter systems and can point me in the right direction? Can you advise me what I need to check to insure I do not have a dead short somewhere?

Again, much thanks for any input you can offer.

Andre

Not that familiar with them either but I would be sure brushes are seated on the armature and not worn out. A weak battery could cause issues as well because as voltage drops amperage increases to provide the same power. Check your battery first, these require a good one. Dead cell = 10 volts.

Thanks for your input, I later found that the terminal ground off the battery was loose and barely touching. This was all hidden when I was under there doing other work, plus, I had moved the battery around some while working. Could have been too loose to start with, and then my shifting of the battery (along with the vibrations of riding) loosened it more?

Sort of upset at myself for not catching that loose terminal connection earlier.

However, could a loose neg terminal at the battery cause such woes?

Andre

FWIW: A friend shared a link to an illustrative schematic at Partzilla that illustrates the starter relay. The power leed off the battery hooks directly to it. It's under the tank on the backbone of the frame.

Now I need to learn how to check it.

Andre

When you push the starter the battery negative is the 'be all' & 'end all' of the system. If loose it'll likely try to earth through something else & 'fry it' [not certain of that comment] but needs a good strong heavy wire earth to work. Relay will be ok. [in my opinion].

Thanks for your input RT325.

The negative/earth wire (that I suspect is not OEM) appears to be 14 ga wire. Should I increase that to 12 ga copper stranded?

Andre

I'm not up on the play when it comes to wire sizing sorry [but i should be]. But the earth would need to be equal at least to the [if original] positive heavy red going to the solenoid & also the light colored green from there going down to the stator. [if i'm thinking right on colors].

Yes, the positive leed to the starter relay appears to be OEM. And it does feel significantly heavier than the 14 ga earth wire.

The new AGM battery is scheduled to arrive late tomorrow, come Thursday morning I shall proceed accordingly.

Thanks again!

Andre

Let us know how the motobatt works I’m working on a AT2 thanks

Will do.

Andre