Vintage Dirt Bike Q & A

Rebuilt the bike this past year. Had a problem with upper RPM power. Winter came, it got cold and I parked it for the season.

A few days ago I pulled it out of the garage to start work on it again. Fired up on the second kick, idled fine. hopped on to take it around the block and it rode just as it did when I parked it for the winter. A few houses from home it suddenly died and would not restart at all.

I changed plugs and still could not get it to start. On two occasions while trying it did kick back on me. After that nothing at all.

pulled and cleaned plug again, held it against the cylinder head as I kicked it, No spark. suspected the timing could have slipped somehow. Hooked up a light to the black/white primary wire and a battery per the service manual and the light illuminated and never went out as the points opened.

Pulled the flywheel and stator, everything looked clean and good.
Checked continuity on the harness and physically checked the wires and no wires appeared to be broken.

removed points and tested continuity. There is continuity when the points are closed and there is not when they are open.

Checked for continuity between wires at the stator harness connector. There is continuity between the Black/White primary wire and the White/Yellow wire on the harness. Is this normal or is this a short on the stator somewhere?

Also, the Black/White primary wire appears to be grounded at all times to the body of the stator. Is this normal or is this only supposed to happen when the points are closed?

Please let me know if this seems normal, or abnormal and if there is a good procedure to check the stator and coils, and what kind of values I should be checking for. I am not too familiar with this older technology, but trying to learn.

Thanks for any ideas!

EDIT: Stator in question:

Hmm, let me try some more specific questions.

Upon closer inspection, it appears that the primary source coil on the stator feeds the Black/White primary wire which connect to the breaker points. the other side of the coil wraps around the stator and enters the interior of the lighting coil. What is going on here? is this wire wrapped up with the lighting coil or is it just grounded somewhere on the on the armature of the lighting coil?

The lighting coil itself has one lead soldered to the armature, the other end exiting the stator as the White/Yellow wire to the headlight circuit and this third wire from the primary source coil disappearing inside. Just trying to figure this thing out.

Who out there rebuilds these old stators?

What did you find out in response to your query about your MT250 Stator?
I have the exact same problem you have. I have a 1974 MT 250 and I suspect the stator .

In your post you said ...."the Black/White primary wire appears to be grounded at all times to the body of the stator".....and you asked ..."is this normal". You also stated that when you removed the points { I'm assuming you removed the points completely from the stator ] that "there is continuity when the points are closed and there is not when they are open}.

I am having the precise same problem as you stated above. But...I did another test......... When I connect the points back to the stator....... all off the bike.........when I manually open and close the points with a multi-meter connected to the points .......the reading is absolutely no different whether its open or closed! I am indeed looking for some Expert Answer: but I suspect that when the points are connected to the stator - - and I am seeing absolutely no difference in the multi-meter reading when they are opened or closed - - is because since the Black/White stator wire is IMPROPERLY GROUNDED to the mounting base of the stator(?).......it is shorting our or making the points non effective! I think the problem is that that BLACK /WHITE wire on the stator should NOT be grounded { that is messing up the workings of the points}! In other words........I think the Stator is bad and needs rebuilding or replacing if the Black/ White wire that connects to the points is grounded to the Stator body.

Is this what you found out? Or did you get some other answer? Thanks............. J_OTAY@YAHOO.COM

It's too bad this web site's search function chokes on the term 'mt250', as there's more info here on that bike than any other site I've seen - bummer. A lot of it's regarding the ignition, too.

A continuity checker or ohm meter will tell you if a winding is broken (open); that's about it. A much better test would be AC volts from the stator ignition coil winding to ground while kicking the bike over; you should get some kind of voltage 'kick' when the points open. New points are a good idea, as it's easy to reassemble the insulators / washers / points spring wrong and short everything to ground.

If the stator has output spikes when disconnected from the wiring harness, then it's a good idea to start checking the stuff downstream from it (condensor, ignition switch, kill switch, coil, wiring, etc).

Ray

_________________
'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

I have a 1974 MT250 and not getting any spark you said the black and white could be grounding did you find out were they were grounding and were the black and white wire hooks up to the points and the other black wire coming from one of the copper coils are they suppose to touch each other Thanks

I have ten honda enduros from the 70's and I have never had a stator go bad. Not saying it wont happen I just think its not too common.

I agree 100%. And even if a stator IS bad, its actual output (or lack thereof) can be easily verified by a voltage check, rather than chasing down wires with a continuity checker which will most likely indicate everything being grounded.

Ray

_________________
'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

How do I do a voltage check!!! Sorry I am new at working on bikes. This bike has been sitting for 33 years I put new points and condenser in it and a new plug. new battery. turn the key on and the neutral light comes on, I have checked continuity all the way up to the plug, checking continuity at the black and white wire should the continuity go out when the points open. Thanks

To check for stator ignition voltage output, unplug the stator connector and hook up the meter to the black/white wire and chassis ground, set the meter to the highest AC voltage range, then kick the bike over slowly. If there's little or no reading, kick it over faster. The reading will be very short duration, you'll have to watch carefully for it. What kind of meter do you have? In general, a better meter gives better results with this test.

The continuity tester might come in handy chasing down wiring harness problems, but it can't tell you if the stator is working.

Ray

_________________
'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

I guess when I put the new points in I put the black and white wire between the insulators and I should have put them on the out side. Fixed the problem and now I have spark. Thank you very much for all the advice.