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Mar 1, 2010

How To Break In A New 2-Stroke Top End

Doing a top end rebuild on a 2-stroke motorcycle is easy and fairly cheap to do, but if you skip the break in procedure your probably missing out on some of the performance gains. It's tempting once you get that new piston in the bike and start it up to go out and see what it can do, especially when you hear the engine run for the first time with the new components. If you resist that urge, at least for a little while, you'll be much happier twisting the throttle later on.

The first thing you must do is CHECK everything to make sure you don't have any missing parts laying around. Look around your work area just to make sure nothing is left. You'll want to make sure the air box is clean and it has a clean filter, you don't want to start out with any chance of dirt getting into those new parts. Fill the radiator up and make sure the fuel is properly mixed with a good quality 2-stroke oil.

Now, start the bike and listen to the engine running. Take it really easy at this point, no quick blips of the throttle to warm it up. Once it's warmed up start making passes back and forth at about 1/4 throttle for about 5 to 10 minutes on level ground. I found myself going through a few gears, but only at idle to 1/4 throttle. Try to keep it in 2nd or 3rd and just slowly accelerate and decelerate when needed to turn around etc. no quick revs, nice and smooth. Some will say to let it cool down after this first cycle, some say it doesn't matter. I let mine cool and then on to the next step.

Next, start making passes 1/4 to 1/2 throttle for about 10 to 15 minutes. After this is done, take a look at your bike and make sure everything is still good, listen and make sure it sounds normal. If everything seems ok, go ahead and start making 1/2 to full throttle passes for about 5 minutes. Listen and make sure everything sounds good, there shouldn't be any abnormal sounds or any excessive heat.


The last thing to do, is a so called "super secret magic" part that really makes the bike run great. I found this online, and I'm not sure exactly what it does, but it came from a good source and it really seems to get the bike working better and gets it the right heat etc. to set the rings. On this part you'll still be making 1/2 to full throttle passes, but shift up a couple gears to where your dirt bike is starting to bog even at full throttle. Keep it pinned even while it is bogging and hold it until it cleans up. Do this about 15 times and your done. You'll have better compression and a longer lasting, more reliable top end.

7 comments:

  1. very useful post for all auto mobilers. Because it has very good advance features like 2 stroke engine break.

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  2. that very usefull tips..thanks for share the tips

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  3. could you do tips for cleaning the power valve i have a cr to and i no your powervalve is the same i dont have a rc power valve i have a 1996 cr250 and we have the same setup but dont know anything about it so would like some help if you could that would be great by the way sweeeeet bike

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  4. Yea for sure, thanks for input! I did refer to the power valve a little on a top end I did, http://www.blazeofgloryoffroad.com/2009/03/top-end-rebuild-cr250-dirt-bike.html but I agree that some more specifics would be a great post. The 96 C250 is a great bike. Basically you want to clean it and make sure all the linkages are moving freely and working correctly. It's all mechanical so it's fairly easy to understand and diagnose. I'll see about digging up some pics/info for a post.:)

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  5. Thanks for the info, im about to restore my old dt trail bike and this really fits my need.

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  6. Making a A New 2-Stroke Top End was almost impossible for me,but your help made it so easy .

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  7. after theses steps I can take it out on the track ?.

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