Vintage Dirt Bike Q & A

I have a 1976 mt125 with no spark. I looked at the usual suspects (new spark plug, new coil, wiring is good, flywheel is undamaged, gap set at .14 mm) so I looked at the stator and saw A) that there was damage to one of the stator coils, and the ground had been broken. So I probably need a new stator. But before I dropped $100 on a new stator, I wanted to check the stator resistance to make sure it was the problem. I have a honda factory service manual, and I looked cover to cover, and it has no spec for the stator resistance. Does any body have the spec? I called honda and they don't have it either.

_________________
1976 Honda Elsinore MT125
1990 Toyota Celica

Here are some better pics

_________________
1976 Honda Elsinore MT125
1990 Toyota Celica

Here are readings from an MR175 stator, with the MT125 wire color codes. The ignition winding reading should be identical to the MT125, the lighting winding reading is probably slightly higher:

Ignition winding (black/white wire to stator ground) 2.4 ohms (points open)
Lighting winding (white/yellow wire to stator ground) 0.3 ohms (approx.)

If you get similar readings to these, all it really tells you is that the windings aren't broken. In my experience, the only reading that matters is the ignition winding voltage output when the motor is kicked over, which cannot be read accurately with most meters. You can try unplugging the stator cable, setting your meter to AC volts, connecting it between the black/white wire and ground, and kicking the bike over. Hopefully you'll get a reading of some kind, but whether or not that will result in an actual spark across the plug gap is anyone's guess; if you get NO reading, though, the stator ignition winding is bad.

Ray

_________________
'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

What is the third winding for?

_________________
1976 Honda Elsinore MT125
1990 Toyota Celica

Battery charging.

_________________
'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

I tested everything as per you instruction. Nada. And I tried the voltage test as well and got nothing. I even tested continuity while kicking and found that the points seem to be working. So new stator it is. Any body know where I can get one? The one on ebay is a little pricey.

_________________
1976 Honda Elsinore MT125
1990 Toyota Celica

Why not try resoldering that ground? It seems like there's enough wire to work with if you loosened the screw and rotated that solder terminal a bit. Also, it looks to me like the coil was squashed rather than scraped or cut, so the wire insulation may still be intact and the coil is unaffected, or worst case you might have some turns shorted together (not shorted to ground) which may reduce your spark intensity a bit, but probably not a big deal.

Ray

_________________
'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

I'll try that first, but my soldering skills are not all that great. I also noticed the orange rubber insulators on the sides of the windings are completely hardened and have crumbled most of the way off. But I'll try soldering it today.

_________________
1976 Honda Elsinore MT125
1990 Toyota Celica

Alright. I soldered the ground, and I checked the spark plug gap, and everything seemed good to go, so I tested for spark, and I got erratic spark, it seemed to vary in strength. I put the plug in and tried to start the bike. Every once in a while I would get a loud pop from the exhaust, but I didn't get it running. What do you think?

_________________
1976 Honda Elsinore MT125
1990 Toyota Celica

There are some pretty decent soldering tutorials on YouTube. I've been doing it for work and my own stuff for about 35+ years, it took a while to get the hang of but not too long. Just be sure to keep everything super clean (soldering iron tip, wire, terminal, etc), position the wire on the terminal first so you won't have to hold it with one hand and solder with the other, heat the terminal and then flow the solder onto it and the wire, and use really thin solder if possible for small work like this. I also use soldering flux which I find makes every flow better, but it's not really necessary.

Ray

_________________
'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

I soldered the joint, but I could only get erratic spark. I bought a stator on ebay with a 14 day "no questions" return policy, and when it arrived the resistance was different from my current one, so I thought I'd try it. Unfortunately,the points that came with it did not close, so I swapped them with mine... Nothing. I tested for voltage like you told me to, and the lighting wire had juice, but the ignition wire was dead. Bad points? I have the gap set right. Or maybe I assembled the points with the insulators in the wrong order?

_________________
1976 Honda Elsinore MT125
1990 Toyota Celica

I've never had to disassemble the points terminal - I just loosened the nut, slid the points wire connector underneath it, then tightened it up. If everything got taken apart, you're going to need an insulator on both sides of the points assembly mounting bracket to keep the spring-steel point holder from shorting to the stator frame. Check for shorting and proper points operation before installing them.

The correct points gap in these POS ignitions is the one that results in a running motor without crankcase explosions (no, I'm not kidding). I would start at .005" (five thousandths of an inch), which should at least allow the points to close. If the points never open or never close, you'll never get spark.

Ray

_________________
'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric