Vintage Dirt Bike Q & A

Hello everyone, new member here!
I am so glad to have found this website and forum. I have spent much time going through each and every page of the “CR,MR,MT” thread and copying off anything related to the MR250. It’s a data base that I know will come in handy as where I live I have no internet so I depend on my saved off information for help when needed.
I have wanted an Elsinore since 8th grade (1973) and finally I acquired an MR250 which the seller boasted as 85% restored and I think he is pretty close with his estimate. The CR 125 was my childhood dream bike but this bike will do just fine. The fat tank and ruby red color is a far cry from the silver and green machine but I have grown to like it.
I bought it (1 month ago) from a guy who had it for 5 years and had never started it. He bought it from a guy who rebuilt the top end and was in the process of stripping it down and repainting components so the guy I bought it from pulled the engine and everything else and painted the frame, bought new tires, tubes, liners, tire stops, OEM fenders, Had the tank “Caustic dipped”(?) and OEM painted, added new decals and clear coated over the whole thing (looks awesome!),new sprockets and chain new OEM side plates, new (NOS) Spark arrestor and much more.
So the bike has not been ran for at least 5 or 6 years and has had all this new work done to it and I have very little left to do to fire this bad boy off!
Both engine side covers had been removed and old paint stripped off so I bought an engine gasket set and painted the covers and buttoned that up. Found an air filter Dennis Kirk, bought what I think are OEM grips, I am adding an aftermarket kill switch for now as I want to start the motor and run through the gears to be sure all is fine before dumping more money into 40 year old parts. It also has a large tear in the intake manifold but again before I spend a hundred bucks on another one I am going to try to repair the existing one for now just to get the bike running.
Before going on I need to say that I have not had a bike in over thirty years so I am not a top notch bike mechanic by any means but thanks to the internet I am working through things. All that is left is to do is reassemble the carb., fix the intake manifold leak and rebuild the petcock and it should run.
I found something strange when I removed the seat, it’s a small (2’X2”) shiny metal box with only one wire coming out of it and connected to one of the wires coming out of the top of the left side cover (magneto cover). It was not bolted down to the bike… just laying there like it was an add-on by the previous owner. I cannot find it on any schematics that I have found( yes, I have an electronic copy of the original Honda repair manual and yes I have checked out all the diagrams on the CMS Parts Lists website).
I’ve included a pic of the component in question and if anyone can chime in with what it is and what it does I would be very appreciative.
Thank you and I will post pics of my bike when I get the thing back together.

My guess is a voltage regulator off of another model. I know Yamaha used Mitsubishi electronics voltage regulators with one yellow wire coming out.

_________________
73 Honda CR250m
74 Honda CR250m
75 Honda CR250m1
76 Honda CR250m1
80 Honda CR250R
79 Yamaha YZ250F
79 Yamaha YZ400F
74 Yamaha GTMX80
75 Honda MT250 x3
66 Honda CA77 305 Dream x2
67 Honda CB77 305 Super Hawk
2009 Yamaha YZ250 2-smoker
2008 Honda CRF150RB

Hmmmm... Interesting.
Guess I have some learning to do.
Thank you for your response.
Here is a pic of my bike when I got it.
Thanks again!!

Ok.. So the regulator does basically the same thing as a rectifier as I understand it. It cleans up the AC from the magneto/alternator and delivers clean 12V electricity to the bike components. The MR is 6V so I assume it uses the proper rectifier to deliver clean 6 volt juice.

There already is a rectifier on the bike, it's attached to the airbox housing so why would it have a Yamaha (Mitsubishi) regulator added to the system? What purpose does it serve?

I have hopes of adding whatever I need to make this bike street legal (I have not checked with the State patrol yet as to what I will need).
Perhaps having this regulator on the bike will help me with this endeavor.
Thanks again for your input.
R.

If that is a regulator it will not work unless it is bolted to a good ground point. Make sure you're getting metal to metal and not metal to paint for a ground.
My MT250 does not use a regulator but it does have the rectifier.
The MT has no regulation to the headlight but has a resistor mounted behind the headlight bucket to reduce the voltage some. I'm not quite sure how that works but it works.

The rectifier has to have 3 wires and it clips the AC current coming from the alternator so you can put DC back to your lead acid battery. This is not regulated, at least not on my MT. It's relying on the alternators low output and the pressure the lead acid battery gives haco in order to not overcharge


I am sure we are all looking forward to your pictures as each phase is complete.
I also drooled over that CR 125 in 1973. Remember that photo on the cover of Dirt Bike magazine?
I've never owned one but I did buy a CR 250 in 1975 and kept it for about a year for play riding and riding wheelies (had laid down shocks and could wheelie forever) and then bought another one in 2005 for vintage racing.

Rick

Thanks for your comments Rick!
I was thinking the same thing about it needing bolted down to a good ground. Because the bike was in a restoration mode when I got it, that may be why the regulator was just sitting there on top of the airbox under the seat. I will look and see if it has a home I can place it. I still don't understand why someone would add it to the elec. system. All diagrams I find show only a rectifier on the MR's as there is no battery to deal with. I mean, if a regulator is not OEM then my headlight and taillight probably have the same resistor you have on your MT.

Anyone else out there that has a regulator on their MR??

I'm sure I will have a sweet ride and and an awesome bike when I'm done but not so sure I will tackle trying to add blinkers, horn and such to make it street legal... At this point that whole project is a quite intimidating to me!

If you get to that point do what Ray has suggested to others and add a battery (lithium ion) that you charge at home. Just size the pack to last your projected longest ride.
My MT250 headlamp bulb will cost over $50 when it burns out. I may add a battery myself at that point. I know I can make a 12V lamp MUCH brighter than this oem lamp.

I have a Chilton Elsinore manual that I can take a pic of the wiring schmatic if you need more info for your bike.

Rick

Thanks Rick! I'll keep that in mind.
As much as I want to get this baby up and running I have a higher priority right now.. Spring Chinook are running and I feel the need to put the hurt on a few of those bad boys.
I am getting close to firing it up and riding it and once I do all other projects will be put on the back burner, I live only a couple of miles from the great Gifford Pinchot national forest and there are 100's of miles of back roads that I hear calling my name.

Guys, this may be a tad off topic, but I think its kinda related. I've been messing with an MR250 also for a few months. Didnt even try to start it, just broke it down for a complete rebuild as it was full of swamp water. I think I have that same mitsubishi box also, I'll have to look tonight. But just today I was reading a bit about the Honda FL250 Odessy line, and how their motors seem to be derived from the MR250 motor. I haven't found anything concrete to back this up except that head and cyl parts interchange, but what caught my attention is that they are CDI based with a 60w headlight, instead of the 6v points/35w headlight of the MR250. If anyone has access to one, it may be worth a look to see if the CDI systems can be fitted to the MR.

Mr. E!! wow, what a name! Why didn't I think of something like that. That pretty much puts you right below the big guy himself, Mr.H! lol.
If you do have a regulator could you please take not of where it is attached to the bike for grounding. A pic would be nice but a verbal description of the location would work as well.
Thanks.