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There is a couple good threads on Thumpertalk in the Yamaha 2-stroke forum on the shift stopper issue with lots of pics to show you what the original and replacement part look like and what the original looks like when it comes apart (outer bearing race and balls gone leaving just the inner race).
If you can find Non-Ethanol pump gas you should be fine.. If not beware.
Funny you guys talk about running or not running pump gas. When I rode it before I never had and issues with detonation, but now that the track I ride has changed, there is one spot where I can hear it crackle just a bit before a large table top. I'm thinking I will mix about one gallon of race gas (100 octane) with every two gallons of pump (91) this weekend.
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Then it happened....I went to a sand track. Suddenly what was "enough" power was waaaayy not enough, and the absence of torque that could be negated with a quick clutch hand and locked right twist wasn't so easy to overcome. My buds on 450s yelled out insults to my manhood as they roosted on by like I was on an a y-zinger. I was miserable. The next weekend we had muddy conditions, and I was miserable again. The honeymoon was over. The bike was going onto Craigslist ASAP. I was done with it. The next weekend I took it to the hard-loamy track to get re-aquainted with my 450 and to meet a potential buyer of the 125 (who never showed). The first time out on the 450 in a while was a pucker-fest. I was quickly reminded that they have a lot of inertia, they numb your arms quickly, you don't ride them like a 125, and the act of turning actually took some thought and planning. By the 3rd lap I was bored and decided to consciously measure how often I had the bike's throttle really, really pinned. The answer was "hardly ever...only on the long straights, and never in corners". Well this isn't much fun. The 125 was sitting at my truck, gleaming in a coat of moto-shine and freshly polished spokes, but I decided to get it dirty one last time....and fell in love again.
The moral of the story is, we all need and should have 125's, but not as your only bike. They suck in sand and mud, but are an absolute hero riot in loam or hard pack. Fortunately they're pretty cheap and a 10-year old one is fine. Parts are plentiful and cheap. Go get one before they're gone.
However, it's important to know what that means.
Most pump fuel sold in the US uses the (R+M)/2 method. That's RON + MON divided by two (or the average of the two octane ratings).
MON (motor octane number) tends to run around 8-10 points lower than RON. Therefore a fuel rated at 93 octane using the (R+M)/2 method should be sufficient.
FWIW, I've been using 93 octane, ethanol-free pump gas in my stock YZ125 the entire time I've owned it (since 2007) and it has never missed a beat.
I also have a friend that was using 87 octane ethanol-free and melted the piston and flaked the nikasil. She thought it was more important to avoid the alcohol than to get the octane. Obviously not.
Check the power valve linkage. Mine was broken. You can buy a new one for over $100 or have a buddy weld/braze it for cheap.
With your weight, you may want to add a tooth or 2 to the rear sprocket.
( I didn't read everyone's posts above, so sorry if this is a repeat)
To the op, have fun and enjoy. I do hope that you are not under the impression that making the switch to 125 is gonna make you a faster rider, in the long run it will make you a better rider. However there is going to be a learning curve in how to properly ride a 2 stroke, especially coming off a 450. Imho everyone should learn on a two stroke. Proper maintenance on a 2 stroke goes along way. As noted I would get the bike working properly, but would not worry to much about spending a lot on suspension at first. Just set the sag and change the oil and seals. (something that can be done very cheap and extreme easy)
Most of my competitive years were on open bikes and there really is no replacement for displacement.
Pit Row
You are planning on keeping this bike for a while, why take any chances? Parts are pretty cheap and working on a 125 is pretty easy.
I know your budget is not really big but if i was you i would look into something like this.
I will look into a top/bottom end kit but most likely at the end of the season as I won't get much seat time before that anyway. I'll probably put 15 hours on it tops and then rebuild the top/bottom end. Thanks for the link. Might as well do that and know that I have a fresh solid motor!!
I think I'm going to start by replacing the shift stopper, changing drain bolt washer, servicing (read: freshening up oils/seals) the suspension, then plastics and graphics (most likely 180 decals). Anyone have other graphics suggestions? Turnaround time is important to me, as last time I tried to go through Bryar (180 decals) he was too busy to really respond to me. I know he races (would be cool to support a privateer) and his work is stellar so I definitely want to use him if possible.
I can't decide where to begin!! Any tips on cleaning the motor to get some of they Oklahoma red clay off??
As for the OP, 180 lbs on a stock 125 you are really gonna have to learn momentum. It will certainly make you a better rider, but you will struggle for a few rides.
It's removed some of the nastiest SE clay stains from engine cases for me. I pour a small amount into a container and use several different type brushes to apply it to the surfaces I want it on (and keep it off the ones I don't want it on).
Mr Bean (lmao btw) I'll give that a shot. I downloaded a manual and hopefully will be tearing her down to the frame in the next week or two.
Anyone interested in me starting a build thread with photos?
Many told me that it was going to be slow and this and that, but as we know, MX is full of guys who have big mouths, atleast on the interwebs. YZ125 is perfectly fine, even with my 200lbs & 6.4
Post a reply to: Making the switch.. 450 to 125