Upgrading to YZ125 Need an Opinion

Around here $2000 will get you 2006+ in good condition.
Things to check for when buying:
Condition of tires
Rims flat, cracked, etc
All the spokes there and tight?
Does the engine crank right up in 1-3 kicks cold? Feel the cylinder to make sure it's cold before start.
Always ride the bike before buying
Engine runs cleanly with good acceleration
Is the clutch 1 finger pull? Does it feel like it's binding? Does the engine bog down when you put it into gear?
Shift through every gear up and down several times
Hop off the bike, check the fork tubes and shock shaft for leaking seals.
Walk around the bike a couple times then start negotiating.

What ever you do, get a 2006+ just due to the forks.

For that price you will definitely get a car on very good condition, so you may just look it in any website, I would suggest on creg's list and you'll be able to find there very good options
Max Lee, proficient consultant on http://payforessays.org/

It is funny I never see this recommended but one thing I do is remove the spark plug (13/16) remove the expansion chamber and shine a light in the hole and check the condition of the piston and the ring. It is very simple to do.

I would look very closely at the clutch side of the case as well. I could clearly see mine had brand new gaskets in the clutch cover and from underneath I could see the side case gasket.

8mm wrench remove the site plug on clutch cover, lean the bike over and check the condition of the fluid and for metal.

Check bearings in the wheels by check for side to side play.

Kick the bike over cold with choke plunger fully down. If it starts the plunger needs replaced because it is a fuel enrichment circuit and will cause it to run rich everywhere.

After it is warm is there a sputtering between the air screw circuit and the main speed jet? Could a fat pilot unless you notice white and an abnormal amount of smoke. Crank seals. But they are easy to fix.

Why not take to clutch cover off and at least look at the basket?

I have an 04 and I love it. I have ridden aluminum frame and am not as fond. Have no idea how good the SSS forks are but I certainly love mine, much better than my 02's 46mm in brake chop and headshake.

No sweat man, blues brother's have to stick together right?

Not sure where you live or who you buy bikes from but I don't think anyone around here would let you take apart their bike. I certainly wouldn't.

I bought a bike that had "new" gaskets visible. Everything was trashed inside, seller was a scam artist and put new eBay gaskets on everything so it "looked" right.

If the bike starts cold without using the choke it probably means the jetting is rich (vast majority of bikes).

White smoke is associated with water or coolant. Excessive smoke dripping down the silencer onto the swingarm is an indication of crank seals.

[i][i]Ok I will bite, once then no more.

Not sure where you live or who you buy bikes from but I don't think anyone around here would let you take apart their bike. I certainly wouldn't.

How many bolts hold the clutch cover on? How many hold the expansion chamber? How many springs? Hardly taking a bike apart and if the person is unwilling then that might be a pretty good indicator it is time to move on. I was encouraging the buyer to protect himself.


If the bike starts cold without using the choke it probably means the jetting is rich (vast majority of bikes).[/i]

If the choke plunger doesn't seat fully it will cause the bike to run rich everywhere. It is a fuel richener not a true choke. On my vintage bikes if I cannot get a jet kit, tapered needles, or a stronger sping, I will use it to help with a lean condition while I ride. If the bike is not running or is idling how does too rich pilot and high speed circuit affect the bike starting cold?

White smoke is associated with water or coolant. Excessive smoke dripping down the silencer onto the swingarm is an indication of crank seals.[/i]

Agreed, so does transmission fluid whether it is for a motorcycle or ATF for a car. Do people run ATF in their bikes? Yes quite a few actually like the friction modifiers in Dextron specifically for clutch feel. In my post I talked about how too much oil affected the way it ran, a farty type noise between air screw circuit and the high speed metering circuit. I personally might be afraid of the bike hydrolocking if it was leaking that much coolant into the combustion chamber. Pulling a plug would tell the tail.

To the O.P.; dude I have been doing this for a long time and here is what I learned; I know way less than I thought I knew. I am more than sure the other advice is plausible and worthy of consideration. Take your time. I got a heck of a deal on mine, smoking deal in fact because I was patient. Your new bike will find you.

mb wrote:

Not sure where you live or who you buy bikes from but I don't think anyone around here would let you take apart their bike. I certainly wouldn't.


Where I live is in my signature. The guy I purchased my bike from was more than happy to let me do all that, he didn't have anything to hide. The good news for you is I would not buy a bike from you.

Let me clarify my point.

As a seller, I know absolutely nothing about the buyer that comes to look at the bike. You could pull my FMF Fatty of the bike like you're going to look at the piston, then hop back in your truck and take off with my parts.

Or the buyer could have good intentions, but not know better. Putting a standard socket set on the metric bolts on the bike. Loose the bolts, strip the threads or the heads of the bolts. Drain my gearbox oil to look at the clutch basket and condition of the oil, only to say "okay well I'll think about it. See you later" Now I'm no closer to selling the bike, wasted my time, and I have to go buy more gearbox oil.

You are correct on the effect of the choke, however it is more likely that the bike is jetted rich vs. the plunger needing to be replaced (on a modern bike). I have never needed to replace a plunger and don't know of anyone off of the top of my head who has. Easy way to test this is to pull (or push) the plunger while the engine is running, if the engine note changes than it's doing it's job.

I'm not saying your points are incorrect merely adding my own information. Like you, I have been buying and selling a long time. I don't let people start wrenching on my bike, but I do insist that they ride the bike (in a secure area that I am familiar with). I let the bike speak for itself.

Check out as much as you can. It's up to the seller, after all, he owns the bike. If you aren't comfortable with the deal, skip it.

Check the cases for repairs, cracks and leaks. The main areas to check are the bottom of the engine, around the oil drain plug and also around the sprocket area. Sometimes the chain derails and cracks the case there. Check for JB-Weld and other epoxy or weld repairs. If the cases were repaired, the bike isn't worth much in my opinion.

Ask the guy if the drain plug threads are stripped out or have been repaired, etc. That's a real pain in the ass to deal with and you don't want the hassle.

Put the bike on a stand and grab the top and bottom of the rear wheel. push with one hand while pulling with the other. Alternate back and forth to check for wheel bearing play. Do this on the front wheel as well.

Grab the axle lugs on the swing arm. shake it side to side as well as up and down. Up and down play is common in the shock bearings. They will need to be replaced in almost every used bike you look at. side to side play in the swing-arm means you need new bearings there...

Grab the fork axle lugs and pull forward then push backward. If you feel play, it's probably in the steering stem bearings. A mis-guided person with a pressure washer will kill the bearings on a YZ steering stem in a short time.

Tally up the costs of the suspension bearings & related parts before you go to look at a bike so you know how much it will cost if you decide to buy a bike with some wear and rebuild those items. Most used bikes have a couple of loose bearings.

Check out the radiators. If they are crushed and/or leaking they are usually very expensive to replace.

To get an overall idea of how many hours are on a bike, check the foot peg pivot pins, the rear brake pedal, the shift lever and the kick starter lever for play and wear. If they are tight, it's probably a "young" bike.

Pop the seat off and make sure the air filter is on the bike and oiled.

Test ride the bike and make sure it shifts through the gears and the clutch doesn't feel notchy. If the shifting is notchy, don't buy the bike. If the clutch is notchy, the bike will probably need a clutch basket and a clutch hub.

Just going into a used two stroke, especially a 125, assume the worst.
At a minimum a used 125 should get a brand new piston and gaskets right away. Be prepared to do a crank and a cylinder re-plate at the very worst.

If you buy a used 125, even if the seller says "I just installed a brand new top end" and supplies the receipts, I always buy gaskets and a piston and pull the cylinder off before I go to the track. If the piston really is brand new, you spent $15 for a base gasket and PV cover gasket to eliminate an unknown about the bike. You should also check the connecting rod bearing for radial play while the top end is off.

If you buy a 2006+ YZ125, pull the carburetor apart and check the jetting. Write it down in your notebook. If the jetting is very far off from stock, it may not be the best setting. The stock setup is really close for most climates.

When I bought my 125 I looked for price first then made sure the frame, swing arm and suspension where all fine. Of course the motor needed to, At least, start... And it did. But I always planned on doing a complete rebuild regardless of condition just so I had piece of mind.

In my experience, go for an 07+ to avoid the shift stopper issue. I bought an 06 with low hours and had to do a full rebuild.