98 YZ125 break in questions.

[ThumperTDC]

Well after about 3 years I finally have my 125 completely back together and ready to fire it up.

If this has already been covered, I am sorry, I dont have time today to search for the answers. I have never owned a 2 stroke before, but I have ridden a few ans well as used numerours 2 cycle engines on various equipment. The service manual I have for the bike says to normally run a fuel mixture of 30:1. To me this seems really rich to begin with. Then it says for break in to run a mixture of 15:1. I understand the need to richen it up for break in, but to me this seems a little excessive. I have seen mixtures to run once full broken in at about 32:1 to 40:1. I will be using honda premix oil. Once it is broken in the bike will be going up for sale, I have no plans on keeping this bike, I just want to make sure the engine is sound before I sell it.

I had to install a new cylinder, crank and top end so I want to make sure I do this right and dont screw anything up. So please if you dont have much experience with top end changes or are simply going to post what you have read else where, please dont post. I am looking for people with experience to respond. I am already into this bike more than what I will get out of it, I dont need to dump more into cause I got bad advise and blew up the top end.

Sorry if this sounds too forward, but I cant afford to F-up the engine cause some kid with no to limited experience gave me bad advice on how to break it in.

Thanks in advance for the replies.

[Rcannon]

You wont mess it up. Dont mess with different gas and oil ratios. This causes problems. Pick a decent ratio and stick with it. More oil can actually lean the bike out and make it run hot.

EVERYONE on earth has a break in theory.

Personally, I like to ride the bike at a decent pace for 10 minutes. Let it cool completly down. Then do it again. Consider bike broken in.

Dont find a sandhill to climb. Dont let the bike idle on the stand while you rev it like mad.

I have never had a problem doing it like this and am sure the same would work fo ryou.

[Blue 250]

For break-in I do 3 15min heat cycles of riding it easy and letting it cool completely between each cycle. If you do this then after the 3 heat cycles dont beat the snot out of it for atleast a tank of gas and you'll be fine.

[SirFallsALot243]

I am in complete agreement with Blue 250.

Additionally, run it at 32:1 through the entire break in process. Richening it up will cause the rings to not seat properly, and in result youll blow it up when you switch back to 32:1 and think its broken in. Run it easy for a full tank on 32:1.

I like to do one heat cycle in neutral at idle before i ride it (15 mins). Then I do a cycle while riding 1/4 throttle and below. Let it cool, and repeat going to 1/2 throttle. Repeat going 3/4. Repeat OCCASIONALLY hitting WFO. After this, just go easy on it until that tank is gone. To be completely safe, I usually do a tank and a half, but thats just me. Good luck with it, and its ABOUT TIME!

[FFRacing11x]

For what it is worth...
Get at least 2 heat cycles in it. Warm it up and RIDE!!! 32/1 is the standard ratio for the 125s. Stick with it. IMO too many guys spend WAY to much time with break in. We are way past the days of iron cylinders and dino oil. Tdub

[crazyrydermx]

EXACTLY what everyone else said. It doesn't have to be a big deal really. All you have to do is ride a little while, let it cool down, ride a little while, let it cool down, ride a little while, let it cool down and your done.
32:1 always!

[HiG4s]

I've had mostly 2-stroke dirt bikes, and I agree with just pick an oil ratio and stick with it. I use 32:1 for 125 and down, 40:1 for 200 and up. But if you feel like changing ratio from 32:1 to 24:1 for the first tank (by the way that is what the local Yamaha shop recommended to me) it can't hurt. While making the gas to oil ratio lower does make the air to gas ratio leaner, the difference between 24:1 and 32:1 (if you do the math) is about 1/4 of a main jet size. Not enough leaner to cause any engine problems, and probably not enough to notice any difference in performance.

I always do three heat cycles with no load, just in the garage, just nice easy throttle, always varying, never more than half throttle until the radiator feels warm to the touch.. And let it cool completely until cyclinder is cold to the touch.. Then easy for half a tank, no more than 3/4 speed the second half.. Refill and ride. Unless it is a Enduro, MXC, or Desert bike with an oversized tank, then I'm just riding before the first tank is empty.

[Rcannon]

I watched a family last year at the track. They were allowing their son to break in a YZ 85 after a lower end rebuild. They would not allow him to go over 1/2 throttle for 10 hours!

It took him two full days to complete the task. We all thought about talking to them...after all, the top end in an 85 will not last much more than 15 hours, but it was very entertaining to watch this poor kid....

[mnewmanfla]

From Eric Gorr: This is what I follow.

Breaking In a New Bottom End

The new lower end will need some patient break-in time. The best way is to let the engine idle for three separate 10-minute sessions with a 20-minute rest period between sessions. You don't need any extra pre-mix oil because the engine load is minimal when the engine is idling.

[ThumperTDC]

Well I mixed it 32:1, fired right up. Was riding it up and down my driveway to warm it up. I pretty much have one complete heat cycle finished. I am thinking I am going to have to go somewhere else to finish it with a little more room than my driveway.

Thanks for the help and suggestions, I think I was more scared firing up this bike, than I was my XR after I rebuilt the engine.

[Henry]

every one here is saying use 32:1 for break in, but i have read(sorry, don't worry it's not for help, just a question)in other sites like this were a lot of people run 40:1 mixtures, is this an ok mixture to run on a 125? one more thing i will have to break in my bike after i do the top end and i run 40:1 (RM 125) sould i switch to 32:1?

[KKXR400R]

I have been running a 50:1 (motorex syn) on Tracys KX125 for 2 years. Never seized, never dropped a ring..nothing. We ran it in from 30-120 degree weather...no problems. After numerous top ends and ring changes we finally sold it this past weekend. Tony, Sounds like you got it dialed in on the break in process. When we broke her bike in we would ride it through the throttle range (not WFO) for about 10-15 minutes and then would let it cool down. We did this through a whole tank of gas. Now. I have never broken in a lower end rebuild, but isn't breaking in a new bike and a lower rebuild about the same? Anyways, Good luck with the bike and have fun.

[Henry]

what is WFO?

[KKXR400R]

Originally Posted by Henry

what is WFO?

wide f#$%ing open, full throttle, ect ect