Vintage Dirt Bike Q & A

Thats exactly how I got mine,someone used the wrong puller and damaged the coils.Sat for many years until I got it with about 1200 miles on

MR Puller: I purchased 2 (one from a mail order cat, the other from my local shop) that were BOTH for the CR...I ended up ordering the real deal Honda part, 3rd time's the charm!

Points: My bike ran so insane all of a sudden. (Smoking, shuddering, coughing, clanking) I thought it was something more seroius... but new points cured all!

OK well, I finally got the points and ordered the puller. So I should be ready to tear in there and see whats up. We were going to use a bearing puller on the flywheel, but then decided for only $15 might as well get the real deal. One thing I was wondering is how does the puller actually work? I got the 20mm long reach that says it fits the MR250, and it just looks like a giant bolt. After I take the retaining nut thats on the flywheel right now off, Do i just screw that puller into in and it just comes off?

Also, any tips on how to get the retaining nut off the flywheel? The honda manual says you have to buy some tool to keep the chain from spinning, but there has to be an easier way I would hope.

Thanks for your help guys, and once I get the puller Ill post more and keep it updated.

I use an air gun impact wrench type of deal it spins the nut right off, you then take the big long bolt and screw it into the rotor till it stops then spin it with the impact wrench a little and it should pop right off.

Alright, so today I got out there and removed the flywheel and old points. Much easier than I expected, it wasnt too bad at all with that puller. I took a look at the old points, and they were only making contact on 1/2 of the surface, and the surface that was touching was sort of like "burnt" looking, with a crusty look to it.

The new points are mounted, but i have no idea on how to adjust them. The manual has nothing on it. I would assume that i pry on that little slot in them, but do I have to rotate the crank so that it gets to the place where the points are at their widest? I dont really understand how they work, it looking like the little felt piece on the points must rub against something on the crank to open them, but I am not sure of that.

Also, while i have it off, I was going to test the stator, Is there anything I should be looking for here with an ohm meter?

Thanks again guys, and hopefully this will get me closer to solving the problem with the MR.

Page 4 of the service manual has the complete points-adjustment procedure. To be done correctly, you really need the battery/light setup, and obviously the flywheel must be mounted to use the timing marks. It can be a pretty frustrating process if you want to get the timing right where you want it; the flywheel windows are really small, the flywheel's magnets are always trying to pull it to another position, etc. If you don't have the light setup and aren't familiar with it, you might want to consider having a dealer or bike mechanic do it.

Oil is applied to the felt strip, which then rubs against the points cam inside the flywheel to lubricate it.

My MR175 lighting coil (yellow wire) read .4 ohms and the source (points) coil read 2.6 ohms, after the meter lead resistance was subtracted. You could also check the continuity of the points wiring and output cable while you're at it.

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 today we went out and put the new points in, aligned them so that they timing lamp went dim right when it passed the "F", and put it all back together, and wala, spark once again. Whats wierd is that the spark is now an orangish color, which I dont know if that means anything. We shook the gas and oil mixture back up, and tried kicking over, and it started after quite a few kicks, and it was still doing the flooded bogging down symptoms that it was doing before. Not sure if the spark has anything to do with this, but tommorow I am going to go out there and check the carb once again to see if anything happened, drain gas from tank, and try a leaner mixture. One question I have is which way is leaner? Me and my father were talking about it, and I think that 20:1 would be a leaner mixture than say 35:1, while he says the opposite, we are not sure who is right.
Thanks again guys

The ratio is pretty simple the first number is for the gas the second is for the oil. So say you are mixxing it at 20:1 that means that if you had 20 cups of gas you would have to add 1 cup of oil and it would be 20:1 so there fore 30:1 has more gas and less oil as your adding 1 cup of oil to thirty cups of gas. I know you dont use cups it was just an example make sure you have a mixture cup it makes getting the mix much easier and much more precise.

20:1 is leaner than 35:1, contrary to what some believe. At 20:1 you have less gas to air ratio than at 35:1. Now, you do have more oil at 20:1, but less gas. And believe it or not, but it is usually the gas/air mixture being too rich that fouls your plugs. The more oil, the more power you will actually get, according to a couple of detailed studies (one of which I actually read a few years ago). But having said that, you can adjust your mixture a bit to compensate for slight alitude changes, humidity or temperature, but adjusting your mixture won't fix your particular problem, as rich as it sounds. Again, what jets are in your carb?? You may have to use magnifying glass to read the numbers after you pull them to look.

Hi guys, well I havent been able to work on the bike much recently, but today I decided that I would try and test the compression again. A few months ago, when I tested it, I got right at about 135, and today when I go to test it its struggling to reach 120. We tested it multiple times, but still would only get to about 120 max. So we had heard a trick of testing rings, in which you put a little oil in the cylinder, and if the rings are bad, this will make the compression go up, and sure enough, when we did this it was getting about 138-140. I am not sure this is conclusive or not on whether the rings are bad, but it is worth giving it a try.

If its the case that the rings are in fact bad, I might just part out the bike. I just bought it as a cheap bike that ran when I got it, and did not expect all these problems to arise. We just dont have the time or money that needs to be spent on the bike. So if worst comes to worst, and I have to part it out, any specific parts anyone is looking for that I can help you out with?

Also, another quick question, if the compression was only at 120, would it still even run. Because the bike wont start at all, and im wondering if its the low compression or bad carb still.

Generally ( and this is a big Generally ) they will run if compression is above about 100. Now, you might have to bump start it at lower compression settings rather than kick start it. At 120, you are due a new top end. But rings are only about $15 or so. A new piston, rings, gaskets, wrist pin and wrist pin bearing will set you back about $140. And if you need to bore the cylinder, another $40. Under $200, which isn't bad. But you still face the problem of the worn carb and maybe worn crank seals. Instead of parting out bike, try selling it whole first. But if you are going to part it out, I'm building a backup engine for mine, so yes there are plenty of people interested in the parts.

As far as the oil test goes, this will hold somewhat true with all bikes, 2-stroke, 4-stroke, good top end, bad top end, etc. The oil will simply help compression for a compression test. Not true with a leak-down test, which would help tell you what's wrong.

I just picked up a 74 MT250 that had been sitting for 20+ years....... kind of went through your same procedures to get the old beast running again.
My carb was goopy............... looked like 20 gallons of premix evaporated into a tiny oily sludge ball, but more like a full tank of leaded fuel settled into the bowl.

Mine starts and runs fine....... the powerband has a nice little hit, then it blubbers out. So I'm fighting a rich condition also.

As for your weak/orange spark? I'd guess that the condensor is going South.
You replaced the points? Get a new condensor also......... doesn't have to be a Honda item... anything from a Briggs&Stratton (or was the Techumsey part the one w/a pig-tail) or a Chevy replacement (I replaced condensors in an old Suzuki Titan w/Chevy pieces).

As for the flooding........... the crankcase might be full of gas.
Remove the plug, unplug the coil lead from the points, put it in 1st gear and push the bike and see what blows out of the engine. A gusher, or just fuel vapor?

20:1?
That'd be one good mosquito sprayer............... oil technology has come a long way since then. I don't see where running a quality oil at 35:1 or 40:1 would have any bad issues.
Backing off the oil content does make a difference in power and throttle response (and keeps plugs from fouling).

Hate to hear you intend to sell the old scoot.
Hope you pull through and get it running again.

Well I had a major doh! moment when looking at the bike today. When I was going through to part everything out to sell it, I looked at the condenser and noticed it wasn't even plugged in! I dont know how i missed that all along, but it wasnt plugged in. So I plugged it in and threw the tank back on. I put a small amount of pure gas (no oil mixed in) in the tank, just to see if maybe it would run without fouling. Second kick started right up, ran it through the RPMs real quick, and shut it off after about 5 seconds of running. It ran just like it used to for those 4-5 seconds. So I was all excited, put everything back together, mixed up some gas at 32:1 this time, put a gallon in, and nothing. Its not even trying to start. At least before every once in awhile it would start but run shitty, and now it doesnt even try. The spark is literally perfect, it just doesnt even try. Any ideas on what this could be?

Its probably flooded. How is the spark plug?? If it is all black and wet, full of gas/oil it is most likley fouled, install a new one and see if it runs then. Also like Ping King said, the crankcase might be full of gas (flooded) disconnect the coil, remove spark plug, put the bike in first gear and push it and see what comes out of the head.

I have a 76 MR 250 and a 74 MT 250 and getting the MR running was a PAIN (lots of the same issues as you) but it runs pretty good now and I love the thing.

Also make sure the timing is set right, I had mine set waay to late and the bike ran like crap, I adjusted it and it was like a whole new bike.

And ping king, do you have any pictures/more info of the Briggs or Tecumseh condensor you used??? I need one for my MT 250.

Hope you get it going!


-Ryan