Vintage Dirt Bike Q & A

im new to this site and could use some help. i have a 1976 mr175 that i cannot get to run or even hit and it is firing and getting fuel. fly wheel is in time, and the compression first kick is 85 pounds and on the second kick it is 120. ive pulled the jug and going to put a set of rings in it. do any of you know where i can get a set of standard rings or do any of you have any ideas why it will not run? any help would be greatly appreciated. thanks steve

Steve,

To get a good compression reading, you really need to kick the bike over until the meter stops going up. It usually takes me at least six kicks to do. I short the spark plug to ground when I do it, to prevent possible CDI damage (my MR motors both have CR125 ignitions). It will run OK with 130psi, but more would be good (mine are both modified for around 155psi, it really makes a difference).

Wiseco 2605KD rings work great (http://www.wiseco.com/ProductDetail.aspx?ItemID=2605KD). You'll have to carefully file the ring ends to set the ring gap; .010" to .012" is good, measured with the ring square in the top of the bore.

If the stock MR175 ignition works, it's adequate for trail riding. Unfortunately, most of the ones I've seen don't work. How do you know you're bike is timed correctly? One of mine screwed up and started igniting the fuel in the crankcase, the other was DOA. Stator source coil and points failure is common. While you have the stator plate out, I would replace the LH crank seal immediately, if not sooner. If this seal is leaking severely the bike won't start, but usually it leaks just enough to allow it to run like crap.

Are you sure the carb is operating OK in addition to being supplied with fuel? The stock carb works fine once it's set up right, which can sometimes take a little work.

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

thanks for the quick reply. i checked the timing with a timing light. i havent even gotten it to hit with starting fluid. one thing i dont know of on the flywheel where it opens the points, it looks like someone put too big of a keyway in it. so it looks like the hump for the points is opening it there.could it be the points are firing twice? also i found after i pulled the cylinder that the exhaust had a few ounces of water in it. do you think that it could be sucking the water back into the cylinder and killing the plug? i just got the bike and its very clean, i just dont want to go throwing parts at it. also do you have a part number or any idea where to get the crank seal? do you think i could get by with the same head gaskets? thanks very much steve

Steve,


Yes - that's exactly what happened with mine, even with the gap within tolerance. I've never had this happen with any other points ignition. This one really sucks.

The water doesn't sound good. I don't know if it shorted out the plug, but I hope not - that may mean you have some water in the crankcase, which you'll have to remove. Hopefully your fuel tank isn't totally rusted inside like mine was. I would definitely drain the tranny oil if you haven't already, and inspect it for evidence of water. It took about five changes for my oil to come out reasonably clear (as you can tell, my bike wasn't exactly lovingly maintained before I got it). It runs fantastic now, though.

If your head gasket still has all the black fiber material intact, go ahead and re-use it - I do it all the time. I run my motor for about five minutes or so before pulling the head; when I've removed it cold, I've usually left chunks of the fiber behind. NOS head gaskets come up on eBay from time to time, along with most of the important parts.

The crank seal is Honda P/N 91204-360-003, and the base gasket is 12191-373-306 (-373- is the MR175 model code). Both these parts are still available. After using Babbitt's Online, MR Cycles, and BikeBandit for a long time, I now use the Web site of my local Honda dealer to order parts, then pick them up at the store. It's a little more expensive, but very fast - and returns are much easier.

I'm probably the wrong guy to give advice if you don't want to start throwing parts; I bought my MR for $180 and then dumped about three grand into it. I've never had more fun with any other bike I've owned, though, so hopefully that counts for something. Just for what it's worth, I tore my bike down to just the frame and motor, and there wasn't one thing I removed that didn't need servicing or replacement.

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

so do you think it is the flywheel that is bad? what would you start with first? after i do the rings, ive done cleaned the tank and boiled the carb, changed fluids with no water. i dont really want to buy all the cr125 ignition stuff yet. i would just like to get it running. then i can do some upgrading. thx steve

Steve,

I really don't know what the issue is with this ignition; the points cam profile, the points assembly, flywheel wobble - I have no clue. The stators go bad too, but I think that's more of a quality or environment issue. The double-sparking and timing problems seem to be design flaws.

One mod that comes to mind might be to file the stator mounting holes into curved slots like the CR stator has, set the points gap really narrow (maybe .005 to .010" instead of the stock .012" to .016" range) to minimize the chance of double-sparking, then set the timing by rotating the stator like the CR. The only difficulty might be flywheel/stator screw clearance. I'm assuming Kokusan used countersunk flathead screws for a reason (the CR uses hex bolts), and you might have to either file tapered-edge or recessed slots, and/or find some different screws (either thin panhead, or smaller-diameter flatheads - the latter could be made from the OEM screws using a drill and file). Check the clearance first though, you may be OK. You'll need a flywheel puller, if you don't already have one (http://www.denniskirk.com/jsp/product_c ... 81953&mmy=). Also, be sure and oil the felt cam oiler while you have the flywheel off; I always forgot this, for some reason.

I wasn't going to suggest the CR ignition upgrade (honest!) because I realize you're not looking to start a big project, and I also don't want to sound like a broken record to everyone else here. I would keep it in mind though, especially if the points ignition just won't work right and defies repair. it's really great to have the CR CDI available, many points bikes have no upgrade options at all. The points themselves are very hard to find, too (Honda P/N 30200-361-003, also used in the MT125).

I've got a flywheel and stator here in a box, let me know if you need any pics, measurements, etc. I also have two spare motors with points ignitions that I can raid for parts, but I've never seen these motors run and can't vouch for their operation.

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 for your help my rings should be here next week and im hoping that will do it but im thinking ignition would you be interested in selling the flywheel and stator if i need it thanks again steve

Steve,


Sure. I'd take them from one of the spare motors, as the ones I removed from my MR are definitely faulty.

When you have the flywheel off, I'd give the crank a few good yanks to check for bearing looseness. I have a funny feeling this may have something to do with the ignition problems, as the MR flywheel is real heavy. Also, if you're changing out the LH crank seal I would inspect the bearing and ball cage carefully. Half of my CR's cage fell out when I pulled the seal, and I'm sure the other half is lying in the bottom of the crankcase.

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

Ray, I got my rings in today got it all back together and i have checked everything its firing it has great compression now, it still want crank i have looked at the seals no sign of oil coming out of them, good and dry i think its the fly wheel where it goes on the crank it is oblong, man this thing is eating my lunch i have got several bike and i have never had this kind of trouble. so would you sell me a fly wheel and stator. thank you very much for your help. if you could, could you give me a call 318-558-0142 or email me at mailto:tinaberry@centurytel.net. thanks steve

Steve,


I just checked out the flywheel I have here, and the points cam lobe on the inside drops off (reduces sharply in diameter) right after the keyway slot on the tapered inner hole. The metal is really thin right here. This flywheel and the matching stator have a little surface rust but otherwise seem OK, and the points look brand-new.

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

well ray i may need a coil too it quit firing i hate to sound like a bum but do you have a coil to i also emailed you also let me no how much shipping and coil if you have one and ill send it through pay pal you are basically given them to me anyway thanks again

Steve,

I sent you an E-mail about the ignition parts.

Here's a link to a wiring diagram, in case it helps - I think it's pretty accurate:

http://alp-sys.com/vintagedbforums/down ... &mode=view

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