Valve Chatter??

[2003rm250guy]

Hello, i got a 03 RM 250,I ride woods an fields an local mx track some. Ive knoticed what sounds like valve chatter in a car under load after about 30 minutes of riding. It doesnt do it under high rev in nuetral,so i dont think its any loose spring,bolt etc. It doesnt do it for the first 30 minutes or so either,only when good an warmed up, and it only does it under load accelerating as it gets on the pipe an on. Its not real lound but it sounds like a few pennies being shaken in your hand. Plz help,its scaring me to death! :ugg:

 

[Jaybird]

I'd buy a top end and go through the motor.

 

[Detonator]

I had a similar "mystery noise" a few months back and feared the worst. Turns out my kickstarter had too much slop, but it was hard to reproduce the condition in neutral or at low speeds. Couple of hardware store 0-rings, no more noise. I hope your situation turns out to be as easy as mine.

 

[matt-itude]

I would check the simple and obviouse first. Its good to give the bike a good once over anyways. Look for things loose, exhaust leaks, check all you fluids good not just for level but condition. Even if you dont find it, one you may find a clue as to what it is and, two you wont do a bunch of work and spend a bunch of money to find out it was just a loose exhaust spring or something. My first thing to check would be the plug for color and sighns of detonation to make sure you havent had something happen to affect your timming or mixture. on a good note typically a piston makes more noise cold because it expands as it warms up. but on the bottom end and wrist pin all bets are off! happy hunting and good luck!

 

[Studboy]

Make sure that you aren't pre-detonating.

 

[2003rm250guy]

thx so far guys...hey mattitude what are signs of detonation your talking about concerning the plug? thx

 

[viking20]

Well , on a dirtbike lots of things can certainly sound weird , LOL ...As someone mentioned , going through he whole bike is a good idea.....I would think detonation is the reason for this.....You say its there after about half an hour , when the bike is really warm , and its only there under load .
It would be easy to see if a fatter main jet helps , and you certainly need to eliminate detonaton , if thats what it is.It can ruin your engine in no time....

 

[reelrazor]

thx so far guys...hey mattitude what are signs of detonation your talking about concerning the plug? thx

"......As previously noted, the air/fuel ratio that yields maximum power is only a shade richer than the one that is most detonation-prone; fortunately, the plug will tell you when there has been even slight detonation inside your engine. The signs to look for are pepper-like black specks on the insulator nose, and tiny balls of aluminum concentrated mostly around the center electrode's tip. Severe detonation will blast a lot of aluminum off the piston crown, and give the plug a gray coating-which is a portent of death for the engine. A few engines will show just a trace of detonation when jetted and sparked for maximum power, but that never produces anything more than a few miniscule spots of aluminum gathered on the center electrode's sharp edges. If you see more aluminum and an extensive peppering evident on your plug, you're in trouble.

We cannot stress too strongly the need to give spark advance your closest attention, because excessive spark lead is the most frequent cause of detonation, which is a real engine killer. You can't stop advance-produced detonation with a cold spark plug, nor with anything but a wildly over-rich mixture. Also, excessive ignition advance has a bad effect on performance. We ran a 250cc road racer at the drags a few months ago, and found that retarding the spark about five degrees from the manufacturer's setting raised the trap speed from 106 to 110 mph. Similarly, there's a 125cc motocross machine residing in our shop which runs a lot stronger and cleaner since it has been retimed for less advance, jetted leaner, and been given a hotter spark plug."

That from Gordon Jennings.

http://www.strappe.com/plugs.html

.

 

[matt-itude]

sorry im so slow to get back to anyone but it looks like there is lots of good help around here and that is what this is all about!I like what has been said. In a nut shell plug inspection!!! If you find no aluminum, specs, or gre but look to be on the lean side, my question then would be what has changed? has something came loose and started leaking air is something partially plugged and i would look there. if you find major sighns of detonation then like has been said ignition timming or major fuel delivery/air leak problem. usually that large of an air leak would make it run poorly and you could find the leak with a can of carb cleaner. If you cant find anything in these areas of concern it still could be something simple.