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Won't reach max RPM, falls flat on top

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Have an 04 crf50 4th 50 I have owned. This one won't pull hard, just falls flat and is about 5 mph slower than my other bikes. Stock gearing. I have played with the needle and the main. Bike runs good, no bog and feels like it is jetted right. Don't know if this is just a sign that it is time to change the rings, or a valve seat issue. It smokes a little when cold.....but it is 35 degrees in Cleveland. Anyone ever have there bike lose power at the top?

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basics- fresh fuel, clean filter, and good plug.

check compression, and look at your plug, what color is it?

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I have searched and cannot find any info as to what compression reading I should pull. Guess I will just test against other bikes that run well. It has fresh gas, and a clean uni air filter. Clip is lowered 1 from stock, and running a 60 main, one up from stock.

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I always thought timing would have to be 180 off if it was off at all. I pulled the jug off. It's the stock piston, and there is some wear on the skirt. Hoping freshening up the top end. Maybe Compression rings are just shot. As soon as I get a hone small enough I will let you know.

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Put new piston and rings in it. Ran the same for about 2 minutes...would not rev up to where it should. About 3 minutes in it made better power and started hiting higher rpm's. I am assuming the rings seating are what allowed it to rev. It's like a brand new bike again. So now, I will treat reduced top end power as symptom of worn rings.

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mmmm, it could have been worn rings, but it could also be other things

I know when me and 2 friends had bone stock brand new 50's from our local dealer, they all 3 accelerated different, and all had different top speeds lol

we all bought them within about 2-3 weeks of each other too!

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