Vintage Dirt Bike Q & A

Having trouble locating points, condense rands rectifier for 1977 MR175.
Anyone know what will interchange with the Om parts?

Here are the P/N's and models:

points 30200-361-003 (MT125, MR175)
condensor 30700-373-153 (CR250M, MR175 - 250)
rectifier 31700-131-008 (MR50 - 175 - 250)

Try Googling these numbers and see what you come up with.

If you plug the black/yellow and black/white wires together, the bike will run fine without the rectifier (in this bike it functions as a pulse former/peak limiter, not an AC/DC rectifier). Mine was wired like this before the CR125M ignition went in.

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

Thank you Ray, you are the Obi-wan or all things MR

Ray could you tell me the why/how you switched your ignition to a CR type?

With the mod you mentioned to eliminate the rectifier, do your lights still work?

Suggestions on how to wire up a rear brake light?

The thread below (along with several others here) go into detail about the CR ignition upgrade:

viewtopic.php?f=21&t=3771&hilit=cr125m+ignition&sid=ad03385ea218af4377af4eb6b9236a3e#p13002

My lighting system still works, but it's been disconnected since I went with the CR ignition (haven't missed it at all). The MR175 lighting system is all AC; the rectifier is used only in the ignition circuit.

The MR175 front brake lever perch already has a hole for a brake switch, and the previous owner of my bike installed what I believe is a Honda switch and wiring to the brake light, which worked fine (no tail light). Later on I added an Acerbis taillight/license plate mount with a dual-filament bulb, and wired up a brake and tail light.

If I were to reconnect my lighting I'd definitely got to an all-LED setup and small gel-cell battery, which will provide hours of bright lighting with no stator connections at all.

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

Just to make sure I understand, I can do the mod to eliminate the rectifier and still run the lights?

Any thought on a maker of a LED tail light/brake light combo or fender?

I was also thinking about turning the tool box into a battery box using some RC batteries. But the gel cell unit would probably last longer. What gel battery would you use?

Yes.

This guy looks like he specializes in converting vintage bikes to LED lighting:
http://www.norbsa02.freeuk.com/goffyleds.htm

This is an example of the gel-cell batteries I mentioned:
http://www.alliedelec.com/power-sonic-p ... #tab=specs

This is the taillight I used - it has a conventional incandescent bulb:
https://www.rockymountainatvmc.com/p/11 ... Tail-Light

Are you looking to actually use the lights for night riding, or are you mainly getting the lights working to pass an inspection of some kind?

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

Pass inspection is my main purpose

OK... well, if you've got the lights already in place, I'd suggest getting a small custom battery to fit in the toolbox, then connect the positive lead to the main yellow wire that powers the lighting (you'll probably do this in the headlight shell; be sure the yellow wire coming from the stator isn't connected to anything if you're using the stock ignition, otherwise you'll fry the battery) and the negative battery lead to frame ground. The battery below should run the OEM lights continuously for at least a half-hour. If you decide to go LED later on, it should just be a matter of changing bulbs.

Battery Station makes custom rechargeable batteries. It's kind of an a la carte menu, you choose your cell - the HR-3U 2300 or 2700mAh looks OK - then there's a 'configurations' link at the top of the page (either style 11 or 24 should fit, but definitely measure the tool box 1st).

http://www.batterystation.com/nicads.htm

I've registered my two Hondas in CT, it was quite easy. They didn't check the lights etc, only the speedo mileage and VIN.

By the way, the CR125 ignition made a big improvement in low end and general snappiness (it adds a bunch of timing advance below 6,000 rpm) and also starting (it retards timing at cranking speeds to minimize kick-back). It's way more than just replacing the mechanical points switch with an electronic one. I had nothing but trouble with the stock ignition, I think it's the main reason why you see so many MR175's sold non-running or parted out at low mileage.

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