how to break in a motor

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May 3, 2001
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#1
I just got my motr rebuilt and i was wondering what the proper way to break it in would be?it is a 02 kx250(doubt that matters)I have never broke a bike in before so what should i do?thanx for any help
 
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#2
Heat cycles, let the bike idle for 10-15min then let it completely cool down. Do this around 5 times. Then ride the bike around staying under 1/4 throttle, and then allow it to cool. Then under 1/2 throttle again let it cool. Then 3/4 throttle, let cool. Then you should be all set. That’s how I've always done it, haven’t had a problem yet. Oh also I would richen up your fuel mixture for breaking it in. Also do a search, tons of info on this site about this topic.
 
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#3
Everyone has their own way, but monkey mouse is correct.. heat cycles.

Richen up the tank. I would skip the 3/4 throttle part and instead, while riding under half throttle "blip" the throttle once in a while to get the engine into its powerband.

After a tank of gas (if even that much) you will be good to go.

Have fun!
 
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#4
Won't the spark plug foul after leaving it idle for that long that many times? I just rebuilt two motors but have not started them yet because of the weather outside. Your input is greatly appreciated. Thanks!
 
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#5
The spark plug may foul because of the combination of new parts + a richer mixture some people initially run, and the fact that you need to stay away from wide open throttle for the break in period. But I have personally never fouled a plug for letting the bike warm up for a while (not idle, but gently rolling throttle)

Like mentioned, everyone has their way. I personally just warmed the bike up for about 10 mins, and ride it around for about 10,15,20 minutes three times. One time under 1/3-1/4 throttle (fouled a plug there) - The next time under 1/2 throttle, and the next time about 3/4 throttle. And from there I let her rip. But I know guys around here that just warm em' up for a few minutes and ride them like they stole em
 
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#6
Do you guys mean richening up the mixture by adding more oil?? Like from 32/1 to 25/1.Doesen't that actually lean out the fuel?? My2cents
 
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#7
No, that won't lean out the fuel. In richening (sp?) the mixture your adding more oil, witch intern there will be more lubrication during the break in period. After you burn all of that tank go back to your normal fuel mixture.
 

Bodge

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#8
If your bike was good jetting wise and it has not gotten colder where you are since then there should be no reason to richen the oil-fuel mixture. Your engine needs the correct amount of Gas and oil to be lubercated properly. If there is too much oil and not enough gas then the engine will be lean fuel wise, which is not good.
 
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#9
Again like said before every one has their own way in breaking in a motor.
 
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#11
Making your bike more rich does not mean adding more premix. The definition of rich is the amount of fuel in the combustion chamber. So a more rich condition means you are getting more fuel then you were before. If you add more oil that means there will be less fuel which leans it out. I know it sounds bass ackwards but that's the way it is.
 
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#12
I warm my scoots up, shut it down, check torque on the head and cylinder, fluids.
Them I go for a ride, not a hard ride, just run the scoot. Nice easy trail.
Go home, recheck torque and fluids again and that's it!
I've rebuilt the top end, loaded the bikeup and raced! Many times!
Joe
 
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#13
What i do is go in first gear for about fifteen minutes second gear for fifteen minutes and so on and so on but dont hold your throttle in one spot always speed up and slow down. DON'T hold it at one speed. And also mix your gas a little richer.
 

DEX

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#14
Im no expert but I would think it has more to do with the RPM range then waht gear you are in. I would think it would be fine to be putting in third gear as long as your not revving it up to get there. I would think first would make it alot harder to keep it at a low RPM while driving for like 2 hours.