Heading to London tonight to pick up my first two wheeled offroader!! Needs some work, but its a pretty good deal I think. I figure I can't loose either way. If I get it tonight I'll post up a bunch of pics for sure. Just can't get away from these 70's Yammies!
MX250
- Thread starter rudy
- Start date
Where in Stone Town you at? Could swing by if its not too late by the time we're heading back. Gotta stop by a home depot for some stuff and drop this hassie off at my buddy's place in Gadshill til I get a little more room in the garage. Will hopefully have it running for some spring shenanigans before the road bikes come out.
Picked it up friday night. Did some looking on ebay and found a few parts, back brake plate (w/shoes?), front cover (is this the clutch actuator underneath?), and some other little parts that I may need to get it running. Still looking for any information on a carb as well as coils and ignition. I think it came with stock CDI (don't know if it still has it), but not sure. Bike isn't at my house, so I haven't had any time to really get a good look at things. A quick look while loading up found there to be two spark plugs??? Is this right or have I done a little too much of the nose candy?
I'm real green as far as smokers go, though I'm sure I'll catch on fast. I've seen some YZ125 carbs as 34mm flatslides. Do 2 strokes have bigger carbs because they have twice as many intake strokes as a 4 stroke would and therefore a bigger carb? The stock boot has an ID of 1.5" = 38mm. I'm not worried about keeping it stock, as it'll just be a POS bike for riding trails and stuff for the summer...... for now. A complete resto may be in the future, who knows. Any info or suggested forums would be much appreciated.
I'm real green as far as smokers go, though I'm sure I'll catch on fast. I've seen some YZ125 carbs as 34mm flatslides. Do 2 strokes have bigger carbs because they have twice as many intake strokes as a 4 stroke would and therefore a bigger carb? The stock boot has an ID of 1.5" = 38mm. I'm not worried about keeping it stock, as it'll just be a POS bike for riding trails and stuff for the summer...... for now. A complete resto may be in the future, who knows. Any info or suggested forums would be much appreciated.
Hey Rudy,
Dropped that cryptic post and then didn't let you know where I was - oops.
Anyway you've got a new project.
I think the twin plug was so that when one fouled you switched the lead instead of changing plugs. It's such a great idea I don't think they do it anymore....
Dropped that cryptic post and then didn't let you know where I was - oops.
Anyway you've got a new project.
I think the twin plug was so that when one fouled you switched the lead instead of changing plugs. It's such a great idea I don't think they do it anymore....
I'm going to take a few more pictures and check a few things out tonight. It was ass-nasty cold out by the time I dropped it off and didnt feel like doing too much by the time I took a few pictures. Hopefully I'll get a few things tore apart tonight to find what I need to get.
So I hear. These things are supposed to have amazing torque. It's such a light bike too. Does anyone know what that thing is in the front right corner of the engine? At first glance I thought maybe it had something to do with the clutch, but then I thought maybe decompression release? I tried turning it and kicking the bike over either way, no difference. There is a cable that goes to it. I'm lost. ???
rudy said:
First off let me say that you have got an AWESOME find there. If you restored it and got it running perfectly,I'd bet some vintage Motocross
racers would pay a pretty penny for it.
OK,I'm not going to even claim I know anything about that particular bike,but I've had a few old 70's dirt bikes including Yamahas.
Putting dual plugs in the heads was common way back when,when they ran much higher oil/fuel mixture ratios and plug fouling on the trail was common. During a race/scramble event was NOT the time to have to stop,get out a plug wrench,pull fouled plug,install good plug well,you get the idea... much easier pull plug wire,switch the plug wire,kick it back to life and GO!
As I said I don't know anything about that particular model,but if it is a later Yammie with an automatic oil pump that may be what the device is under the front case. In fact after looking at that one pic I'd bet good money that's EXACTLY what it is. I bought a Yamaha 100 Enduro with one. Long story short,some idiot(not me ;D) routed the line from the oil tank to the pump wrong and pinched it under an engine cover resulting in massive rod bearing failure due to NO oil getting to the engine internals.
The pumps were hooked by cable to the throttle cable and the mechanical pump regulated different oil/fuel ratios depending on the throttle position.
They only turn/run when the bike is running/turning over and even then they turn pretty slow and mine at least would make a little 'ticking/clicking" sound as it turned.
Many racers took them off,put on a block off plate and just ran premix to insure that they always had oil going to engine. Of course the ratio was static then for ALL rpm levels and could lead to fouled plugs if the carbs loaded up for too long depending on how rich the mixture and state of tune the engine was in.
For what I've read and heard the Yamaha systems were pretty reliable though(if the lines AREN'T pinched/blocked!) and they went with it I think for all their later two-stroke street bikes after awhile to cut down on emissions,oil waste,excessive smoke and plug fouling,etc.
If that's what it is make SURE it is working properly and set up correctly or else your better off removing it,putting on a block off plate and running premix in it.
Depending on the year and model 250,250A,DT etc. it COULD have a compression release/decompression valve and very,very likely an oil pump.
If your model DOES have a compression release fitted it would be by cable also and the release would be close the the exhaust port in front of the cylinder most likely on the right side of the cylinder as your sitting on the bike with a cable running off of it,up and over the head to the rear by the carb. Many times these will freeze/rust up and won't work anymore and have to be fixed if you want/need to use them.
Some or at east most that I have seen have their own little lever,like a small brake clutch lever up on the handlebars and some are automatic/mechanical and work when you kick over the engine. The Yamaha version it the pics below I don't know how it is activated?
Here's one example:
http://www.bikebandit.com/houseofmotorcycles/yamaha-motorcycle-mx250-1973/o/m7397
Thanks man!! You shed a LOT of light on my situation. I think you're right with the oil pump idea. Makes a lot of sense as I have the split throttle cable. It's in pretty rough shape, so I'm thinking of running premix and just a normal single throttle cable and forget about the oil pump. I ordered some manuals yesterday, should wait til they get here before I really start tearing into her.
rudy said:
Your welcome.
One thing though,if it has a compression release I really don't understand why? I had a CR450 with no release and although I had to be careful how I kicked it I never had trouble kicking it over,and over and over(it didn't want to start cold!). Even after I had it rebuilt and it had full factory compression restored it wasn't that bad. Most two-stroke singles don't have a lot of compression. Most off-road bikes with compression releases are big old four stroke singles. Those I could maybe see why you would need that feature,but not on a 250 two smoke?
Anyway,I think they used to make some aftermarket releases that would screw into the second spark plug hole on dirt bikes with dual plug heads like yours. I think they used the cable,handle bar lever set up. I could be wrong,but I think I remember seeing those quite a few years ago.
Ah Yes,here are some after market types for hard kicking Harleys anyway:
http://www.jpcycles.com/groups.aspx?LID=ee35cd18-0412-4e15-86fb-215b8c7de029&DID=e71a7b64-ca6e-4f44-bb52-8bbde776554e
http://www.av-v.com/CompressionRelease.htm
Dan's Yamaha release:
http://www.dansmc.com/comp_release2.htm
I guess my memory is still intact after all!
Well, just spent $300 on my $200 bike! Lol. Found a guy on ebay that was parting out a complete bike. He hadn't sold anything yet, so I got first dibsies. Whole ignition, some covers, rear wheel parts and complete carb (he is even gonna clean it for me!!). Other than that, I guess it'll be new tires, sprockets and chain. Likely change the tranny oil while I'm at it. Paint the tank and bolt down the seat and I'm good to go! Should be fun, can't wait for some 2 smoke action!
Lol! That would be sweet!! Don't give me too many ideas, I might do it. I'm running it through my mind now..... lower suspension, alloy tank, clip ons..... NO!!! Don't have the money for that!! I already have too many bikes! (That's what I keep telling myself, but haven't convinced me yet.)
