rap tap noise

[tcuda499]

hey, I just did a new top end on my 04 cr 250. I used a pro lite piston and drilled out the holes for the exhaust brigde. i did 4 heat cycles to break it in and noticed no problems. went out sunday for a 12 mile loop and noticed about half way into it a noise from the engine right before the power band really hits hard.its kinda a tap,crack noise thats very fast like piston slap but is only about upper midrange. No low end noise hot or cold and top end sounds fine. Its just at a certain rpm it makes it.I did notice the noise very little before doing the top end but it was more like a single crack noise at the same rpm as now.i'm wondering if i didn't adjust the RC valve cables right but the bike has lodes of power.also would this poss be a lean condition as where a pro lite piston may differ than the stock piston that was in it?Also my gas was a little old,3 months, bad on me!!!I haven't had much of a chance to look into it (baby on the way!!!)yet besides a wash and a quick ride to dry. what do you guys think? thanks. :think:

 

[snb73]

Did you loctite your the bolt that connects to your power valve actuator to the powervalve pivot rod? I had mine come loose once, and it made a very distinct noise.

Hope it helps, Steve.

 

[tcuda499]

no I didn't. but a quick and easy check for tomorrow.thanks

 

[kx125412]

That was happening to my YZ250. For me it turned out to be piston slap and a little rubbing of the powervalve. New topend and shaving of the powervalve and now no more noise.

 

[2strokerfun]

It may be some detonation. Try fresh gas and a notch or two richer on your needle and go from there.

 

[tcuda499]

thanks everyone but i still haven't made it to the garage yet. hopefully wensday i can get something done on the bike....

 

[tcuda499]

well I checked the RC pivot and the nut is tight.i knew it couldn't be that easy. i'll try fresh gas and mess alittle with the carb this weekend.Anyone else have any ideas? thanks

 

[kx125412]

Bottom end bearings that are really bad and knocking? Although if it would be that, it should do it at all rpms and get worse as the rpms rise.

 

[tcuda499]

well I cant see it being the bottem end. It really didn't make this noise before the top end rebuild and doesn't do it cold. In fact I didn't notice it till about an hour and a half into the ride. I got it home and washed it and took it up and down the street and it made no noise? i'm leaning towards bad gas and running a little lean.i'm no carb expert but I do have a manual.Do I have to take the carb off to go richer on the needle?

 

[tcuda499]

well i finally got to touch my bike this weekend. I changed the gas and went to the third clip position. it was on the second. the manual states the third clip position is for really colder weather and higher elevations but i will give it a try. soon, hopefully. thanks everone.....