Vintage Dirt Bike Q & A

I have (3) 1975 MR175's that I cannot get spark. I have seen suggested that I should convert them to a CDI using CR125 parts. Can anyone tell me what parts specifically I need to obtain and install? Also, is there a way to maintain a working headlight/taillight, or do I need to add a 6 volt battery?

I use complete CR125M ignitions (stator, rotor, CDI box, and coil) on both my Hondas. You may be able to use the MR coil by grafting on another connector, I never tried it. The stator and rotor bolt right on, you'll have to get creative mounting the coil and CDI box.

Ideally the entire ignition should come off one bike. The stator/rotor set MUST come off one bike, or have the same two-character code and series number stamped on both units.

If you do a lot of night riding, you may be able to find LED replacement bulbs and use a small gel-cell alarm system battery or similar. I never really rode at night anyway, so I don't miss the lights.

The heavy OEM flywheel contributed to crankshaft balance, so the motor will vibrate using the CR rotor. I've gotten used to it, along with the big performance boost from the CR ignition.

Ray

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

My bikes are 1975. What year CR125 will work? Will any other model work as well? And does anyone know where to find a reliably good set cheap?

Any year CR125M ignition ('74 to '78) will work. I prefer the later '76-'78 ignitions with the 400 codes, as the timing marks are a little more usable with the MR motor.

I got all my ignitions off eBay. Look for parts with little or no rust, good cables, and no visible damage - sellers with a good return policy are also a safer bet than no-returns guys. I think the most I paid for a complete ignition was $120 shipped.

Here's the eBay search I used - it finds a lot of other stuff, but shouldn't miss anything:

http://www.ebay.com/dsc/i.html?LH_Title ... rive&rt=nc

My advice is to be patient, these ignitions are always popping up and some are even reasonably priced. In the meantime, why not try to make one working points ignition from the 3 you have? You might find one each working stator and coil, and a flywheel with enough cam height left to still open the points. Run the points gap as narrow as possible, like .008" or so.

Ray

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

I have put about 16 hours into playing with the points on two of the bikes. I had one running, but when I opened the throttle past 3/4 it was bogging, so I nailed it, it started backfiring, died and wouldn't start. It only backfired. I took off the flywheel to adjust the points, and I noticed that the flywheel was cracked where the key fits, and the brush on the points had broken. I replaced the points, and flywheel, but couldn't get spark. When I hooked up a battery and test light, the lights wouldn't go out or even dim. I noticed the stator was corroded, so I replaced it. Still, there is no spark, and the points don't open, the light doesn't go out.

On the second one, it never ran or gave spark, but I can get it to open the points. I cleaned the points and regapped them, but still no spark.

The third bike is missing the stator and flywheel. While I still have multiple stators, I don't have another good flywheel. I haven't seen this one run either.

I am not very adept with electricity, and gapping these points is practically impossible (I can't find a tool thin enough to fit through the hole and not twist open the points).If anyone has a suggestion or easy to follow plan to test the system, I would appreciate it. Alternatively I will continue to look for the upgrade to cr125.

You could probably put another 16 hours into those ignitions and still end up with nothing, or - at best - very low-quality 60's-era technology that will likely crap out again within a few months. Far better to put maybe 4 hours or so into the CR upgrade, and then get at least some idea of what the bike is capable of.

Ray

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