Vintage Dirt Bike Q & A

For the MR guys with the CR ignition setup, I've stumbled across some info recently that might be of interest.

First off, check your rotor and stator to make sure they're the same version. The rotor is marked on the face, and the stator markings are on the backing plate on each side of the bottom bolt. I have a 3E 360B rotor and a 4B 360B stator on the MR, and a 4B 360B rotor / 6A 400 stator on the 175cc CR.

If the rotor and stator match, you're fine - you can use the stator mark and the rotor 'F' mark to set timing with a dial gauge. I was running 2.0mm (@ 21 degrees BTDC) advance, but now it's set at 2.2mm (21.8 degrees), which definitely gives more low end/mid grunt than before. The CDI box adds about 12 degrees advance below 6,000 rpm; to my eye it looks like it kicks in pretty quickly between 4,000 to 6,000 rpm or so.

If the rotor and stator don't match, you may have problems. I thought all the CR125M ignition components were functionally the same, but they aren't at all; in fact, it looks like Honda was continuously updating the ignitions nearly every year, and possibly mid-year as well. There are at least three different rotor/stator setups, and probably more (I haven't checked the MT125R setups).

My 6A 400 stator has its mark 1.5mm (6 degrees) to the left of the mark on the 4B 360B stator. This is surely why the 'MC175' has had weak power - and a beautiful idle! - from day 1. I have four rotors and three stators, and except for the two 360B rotors all the markings are different.

By the way, I've been working on the assumptions that the stators are identical (for timing purposes) except for the timing marks, and the rotor magnets all have the same relationship to the shaft keyway for balancing.

Ray

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