Vintage Dirt Bike Q & A

so I bought a $80 first bike...

it's missing almost every mechanical control so I figured this is where I would ask questions

now my first task is JUST MAKE IT RUN! I got lucky and the engine has compression and the carb doesnt look too bad.
I ordered a carb off ebay for a 93-94 CB just to get the throttle parts that go in the carb and the twist grip.

so here's the first question. will a throttle cable from a NSR125 work? as I figure you have to pull the oil pump and the throttle at the same time. here's the ebay link http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... K:MEWAX:IT item number: 350349519476

I'll have more questions as the build progresses so I thank all of you in advance, NOW SOME PICTURES of what $80 of can return money can buy

Cool old bike man..........

I had a 77 XL100 and my best friend had an MT125......... I remember it well, and that was over 30 years ago.
The bike held up really well, only thing we ever did to it was replace piston rings.

As for your throttle cable?
I'm not sure if the 'bay part will swap in.
I know there's a way to replce individual cables, so you might just swap out the top cable and leave the lowers original (might be pump adjustment issues w/the new one).

You plan to strip the lights or put it on the road?

Does it have spark along with that good compression?
If so, your half-way there of making it run.

Good luck.

I dont have ANY throttle or oil pump cable, those were removed as was the original coil and condenser

some old coil was in there and not hooked up right. I bought the correct part off ebay for $20 so hopefully between that and a new battery and minor repair on the harness, I should have good spark

at first this will be MILD off road until I build u funds for title, registration, training, insurance and misc expenses so the lights are staying

Wow........... sorry.
I didn't realize that the throttle cables were missing also.

I just brought home a 74 MT250.
It was stripped of all lighting, but otherwise pretty much complete.
It sat for 20+ years......... I cleaned the tank and carb and got it to run w/little effort.

It doesn't have a battery and it cranks up fine. Actually builds spark w/minimal RPM from the kicker.
So I'm guessing that yours will run also just from the stator, and not needing a battery.

If your flywheel cover is intact and sealed tight (no rusty parts inside), hopefully the points are good and function. Then you'll need to scrounge up a condensor and coil.
The condensor is mounted to the coil on my bike.....not sure about yours.

yeah my cover is missing, I suppose I'll have to check it

a couple coatings of brake fluid later



you can start to see the 1973 colors!



here's how I coated it, I ragged on some brake fluid then soaked some disposable rags and put them on the tank to sit for a few hours





and here's tomorrow project, check the points and oil pump and make sure the engine is ready to go back in



I STILL NEED AN IDEA FOR THROTTLE CABLES!!!

the throttle cable finnally listed on ebay!!!! woo hoooo

and I got the tachometer for $8 !

re wired the blinker relay and front headlight plug





notice how I did it so it should look as factory as possible yet keep my costs down. I'll rewrap most of the harness in new tape because some of the original tape is aged, and I still need to find some heat shrink to cover some cracked insulation and my splice to the front headlight

got the carb I bought off ebay in today, found out it was WAAAAAY wrong, but at least the twist grip will work. time to start re-selling parts

*edit* damn twist grip is wrong too... anyone want to buy a complete carb for 93-94 CR125

I'm so new to this I have no idea what I'm doing

got the ignition coil and condenser and shift pedal in today...

put the motor and wiring back on the chassis. no luck on spark yet. also the suzuki kick pedal isnt working out, so I'm gunna have to splurge on the right one and sell this one.

any quick ways to see if the points are throwing charge? I assume the input lead on the coil should be 6V so I could maybe test that, and do a continuity from the frame side of the motor plug and make sure the switches are working (yes I switched to run and turned the key on, I got lucky on the kid finding the keys)

The points stay closed during part of crank rotation. The ignition fires when the points break contact........ or the instant they open.
Also if the condensor is bad/weak, it'll have a weak spark, spark once/twice, or won't fire at all.

You can use any battery to test the points, or even use a battery with jumper cables...........
Connect a test light to the + side of a battery, and the other end to the points wire, and make sure the bike is connected to the - terminal. Turn the flywheel and see if the light turns off/on. If it stays off make sure the points are clean and that they open/close.
Most prob's I've seen are just dirty/rusty points. A little strip of sand paper and WD40 usually does the trick for a quick cleaning.

The coil is powered up by the ignition stator. You could probably connect the test light to the stator power supply wire, kick the bike over and see if the light comes on.
Hopefully you have good wiring/internal parts and your system works.

I'm not sure exactly how a point system is wired, but I'm guessing the stator powers up the + side of the coil and the condensor and points are wired to the - terminal.
I looked online for a wiring schematic but couldn't find anything.

Good to see you're making progress.

Just a word of advice from someone who's been searching for various MT, MR, and CR parts for the last three years; stick with Honda MT125 parts for now. There are tons of them on eBay and all over the Web, with more arriving all the time. You'll save yourself so much grief.

+1 on Ping King's ignition troubleshooting procedures.

Ray

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

I got my used $8 tach in today, looks decent for the price...

anyone know how to take the face out and clean it / touch up the piant?

All I know is to NOT use windex. Did that on a car speedometer once--removed all the flourescence and I could never read the numbers at night after that !

That's good info, thanks for that.

So I have a question............... I have an MT250 that all the lighting was stripped off of.
Will MT125 assemblies fit on an MT250?
If I remember right, some of the tail light pedistals had 3 bolt mounting and some had 4 bolt holes.
The headlight/horn/blinker bracket uses 3 bolts to secure it to the upper and lower trees.
Would that interchange also?