Vintage Dirt Bike Q & A

I have been around bikes for over 40 years and remember well the introduction of the legendary CR250M Elsinore, the bike that changed motocross and off road riding in general forever. Then there was the other models in the Elsinore line, and correct me if I am wrong, but they all started or stemmed from the CR versions and were detuned and regearded for other uses, such as

CR250M - begot the MR250 and MT250, the MR being closer to the "real thing" than the MT250 which was a dual purpose bike.

CR125 - begot the MT125 and possibly the MR175 (bigger jug and head)

This being said and the fact that I am knee deep into a restoration project a 1976 MR250 (always liked that one) what are the similiarities and what parts interchange. I can envision some things like gaskets, sprockets, cables. But would think the jug is different and possibly the carb - between the CR250M and the MR250.

Personally I think the MR250 was a great woods bike that was overlooked in it's time, as it had to compete with the Pentons and Husky's of the day. The MR250 I think was a CR250M Elsie, geared and ported different for more usable power in the woods. Right or wrong?

Jug is only slightly different. I think the exhaust port is 1mm lower on the MR, but you can easily interchange the cylinders between the MR and CR. The main differences are that and the following: carburetor; heavier flywheel; stator; points; wider spaced gears in the transmission. I think everything else is the same in and on the engine. On the frame the differences are: the tank, a longer seat, black frame instead of red (for the 76 year which is the only one the MR was issued in); white fenders instead of red (for the 76 year); brake pedal is steel instead of alloy; kill switch slightly different; lights and light switch and wires for the lights obviously not present of the CR; front tire spacer for speedometer gear and speedometer obviously not on the CR.
That is all I can think of right now.
Now the MT is way different than a CR or an MR, but I believe they share the same lower engine case, crankshaft and piston.

Just curious, have you found a source for white fenders?

There were a couple of rear fiberglass ones people on this have offered, and I've bid on a couple on e-bay, but I always tried to get them on the cheap and keep the griping in the house at a minimum. You see a lot more front ones offered than rear. I recently put on an Acerbis rear universal that fit really well (doesn't go down to cover the air box as far as original) and looks really good. It was $14 at local Cycle Gear store. Had to cut indentation for exhaust and drill two 3/8 1/2" holes for side bolts and a 1/2" hole for rear rubber plug/bolt. It looks like it belongs on the bike, but I still want a replacement original sometime. My airbox will eventually get chipped up with the Acerbis. I keep hearing DC plastics will start making '76 fenders, but last time I looked, they don't. And red racer is obviously out as a source. So, I guess the answer is "no" for a new one.
Oh, and I forgot in the previous post: the MR has the chain guard the CR doesn't.

I don't think that the MR had the saem "hit" in the powerband as the CR either correct? as the CR as we know was a Motocrosser and the MR a woods bike.

Speaking of fenders for it I found some at vinatge iron and also via Dennis Kirk - UFO white plastic universal fit, looks pretty good and probably what I will use.

Well, I've never ridden the '76 CR, but from what I hear, that is correct. MR has better low end, probably due more to the flywheel than the 1mm exhaust port difference.
Having said that, the MR is a bear to get and keep jetted properly. They are rich from the factory, especially the 48 pilot jet from the factory. Also, too much slow riding and mine can tend to get a bit hotter than I like. I feel mine is best on wider trails, fields, fireroads and gentle old-style MX tracks. I think it is important to have a 13 front sprocket for tight woods riding.
As far as universal fenders go, some of them I looked out were just too round. The factory fender is really a stylish piece with good lines and a couple of good edges. But I have seen these bikes with the rounder fender and they do look good. Send me your e-mail address and I'll take a pic of my Acerbis and send it to you. I really like the way it fits the bike.

yes please send me some pictures of the acrebis fenders and also the part #'s ! I liked the OEM fnders too but finding a pair of them is no longer possible.

oops e-mail address is mailto:a6chris@msn.com

what was the factory reccommended fuel / oil mix for the MR250

20:1, but I run 32:1 and get a little less spooge.
I have the honda service manual I can copy and mail you sometime. Invaluable when working on the bike. My docket is hellish next week, but e-mail your address to my home and I'll try and copy and mail it in the next couple of weeks: mailto:mitchie@valornet.com

I threw the bag away and don't have the part no., but go here:

http://www.acerbis.com/p149_universal/rear_fenders.html

It is the top one, nost rear fender. There are two sizes available and you need the larger one for the 250-sized bikes. I'll try and send pic this weekend.

Mitchie, ok man thanks! I will e-mail you my home address for the manual. I like that acerbis fender alot better then the UFO ones, did you use an acerbis one up front too?

now if I can only get the frickin piston unstuck...

Welome aboard the MR ship!

76 Red CR frame is chromoly, 76 MR black frame is "mild steel", CR frame is lighter, but missing the toolbox bosses.

CR forks had threaded tops, where MR's have the circlip/plug. CR seat will fit, it's lighter (plastic base), shorter on the tail end, but won't fit if the MR airbox top lid is on. Not a big deal.

75 CR white plastic fenders are the same as the 76 MR. I think DC has them. CR bars were black, MR chrome.

A Preston Petty enduro fender with tailight looks good on it!

Yes, the carb can be a pain. original muffler is awful, heavy and chokes her up. I've run a supertrapp fro years, much snappier.

A CR will kick an MR's butt in a race, but the MR is much more forgiving in the woods! If you plan on running it, vs a restore, get new shocks, as the stock ones are just pogosticks and will bounce you around in the rough stuff. Have fun!

Oh yeah, the head gasket may be thicker on the MR.

Almost nothing from the TM will fit, and except for the controls and one side panel, the MR175 is a different dog too!

Gas tank on the 175 looks the same as the 250, but it's not!

I'll post more if more comes to mind!