Vintage Dirt Bike Q & A

Hi There. Just found this site, and hoping it will help me out. I have a 74 MT 250 that sat in my dads barn for 5 years. It ran before that. I changed the battery, fuse, cleaned the carb, new fuel line and filter, spark plug, and still am not getting any spark. There is compression. When I turn it on, the headlight or indicator lights are not coming on. They did come on this past summer when I stuck a fourwheeler battery in it, but then the fuse blew and they have not since. I did get the right battery, I know the battery is good because I bought it today and the shop had been charging it for me. I put in a new buss fuse. It is a tiny bit longer, is this important? If so I will try to find the exact size as the stock one. I changed the ignition because the key was broken off in the old one. Not really sure what else to do, keep in mind I am a 23 year old girl so I really don't know a whole lot about the bike. Someone told me it could be the point in the stator. I took the cover off, but can't get the cover that spins around off in order to try and find the points/what they are. Any help at all would be really appreciated. Just would love to get this thing back in running order. Please email me at mailto:hrthompson22@yahoo.com or reply here if you can be of any assistance. thanks!!!

First thing is you don't need a battery for the bike to run. The battery is only for stuff like the tail light. You do need a battery in it to be street legal.

You only need to pull the cover off the left side of the bike and rotate the flywheel to see the points. The slots in the flywheel are indexed such that you can check the points gap when the slot is over the points.

It is a really simple ignition system, about like a lawnmower. Your friend was probably right about the points being a problem. You can ask for a "Points File" at any automobile parts store and they will probably have one. If you are in a hurry, you could just use sandpaper or a finger nail file to clean the contacts. The contacts of the points frequently oxidize or get gunk on them. Once you get them clean, you should set them when opened to ~.015". This is about the thickness of a business card.

For ease, leave the spark plug out but laying on the engine so it is grounded for checking spark. Makes it much easier to turn over the engine w/o breaking a sweat.

Rick

You should have a 6v battery in it now if you did get the right one. I'd start with double checking the fuse you blew, for the headlights. But you should be able to get a spark without headlights working. I'm guessing the four wheeler battery you earlier hooked up was a 12v battery. I'm electrically challenged, but I'm wondering if that might have damaged something, like rectifier. Hopefully someone smarter than me will respond about that.
As far as the flywheel goes, you'll need a special flywheel puller that costs about $13 to get it off safely without damaging the windings beneath it. Good luck!

thanks for all the pointers, i will get a new fuse and a points file tomorrow. i looked in at the points, still not really sure which the points are because there was a bunch of wires and coil type things on the stator, but i will see what happens. I have another rectifier sitting in a box, so will change that also before i try starting it again. any more input is greatly appreciated.

easiest way to clean points that are just a bit dirty is to run a dollar through them a few times when closed. If then are corroded, though, filing is the way ( or really replacement ).
To see what you are looking for, go here, about 2/3 down page and you'll see picture of MT250 points:

http://www.re-mx.com/cr/cr125_cr250.php

Thanks mitchie, I will look at it tonight. Would it make more sense to just buy the new set of points in the link you just gave me? Is it difficult to install them? Another question, you said run the dollar through them when the points are closed, how do you open close them? Is that what happens when you spin that cover that is over the stator? Sorry if these are silly questions, thanks so much for the help.

In my experience you can usually clean the points while they are still in the bike just good enough to get it to run. All filing or cleaning is much easier if they are out of course, but that is a lot of work. By all means if you are planning on taking it on a long trip, replacement would be the way to go. Let's see if I can get a picture from my Haynes manual to upload that will help you spot the points with the info mitchie gave.


Rick