Bike sounds like a can of marbles!

MilkJuGGz · Oct 3, 2002

Hey everyone!

I have a 96' WR250 and I'm trying to diagnose a rattling sound that I'm hearing. It sounds like a can of marbles being shaken around.

It happens when opening the thottle fully when in 5th and sometimes 4th with the engine rpm's really low. I know it's not exactly useful to ride the bike in too high of a gear at slow speeds and open it up, but it doesn't sound normal. The rattling sound lasts only two seconds at most, and is long gone before the bike's making any usable power.

Bike is at good compression, power is strong, and jetting is a tad rich. Transmission works perfectly fine and shifts cleanly.

It sounds like it could be comming from the exhaust system rattling at a certain frequency. Perhaps the hose clamps on the guard I have are vibrating at those speeds? I'm just worried that something is wearing in my transmission or the piston is slapping around.

Please tell me my baby is fine and that this is normal and I don't need to have something costly replaced! :scream:

Thanks in advance!

~JuGGz

Rich Rohrich · Oct 3, 2002

What you are describing (high load, low rpm, high manifold pressure)sounds like detonation. If the sound dimishes by closing the throttle some it's a pretty good bet you need higher octane fuel or less ignition timing (or a combo of both).
You can usually spot the signs of detonation on the plug. It will looks like little balls of aluminum or pepper like specs depending on the severity.

Ultimately it's probably easier to just downshift and bring the revs up. As the rpm increases the powervalve will open and lower the trapped compression ratio making it much less likely to knock or detonate.

MilkJuGGz · Oct 4, 2002

Thanks Rich for the info.

Guess I should get a thumper if I want lug it around in high gear :-)

IrishEKU · Oct 4, 2002

Originally posted by MilkJuGGz
Thanks Rich for the info.

Guess I should get a thumper if I want lug it around in high gear :-)

:think: I guess I just don't know but isn't the WR a thumper? :confused:

Senior KX Rider · Oct 4, 2002

Yamaha made a WR 250 2stroke for years. Not sure when it was discontinued

MikeT · Oct 4, 2002

I've heard that sound before from any bike that has a worn out chain. The chain clicks REALLY loud and sounds terrible. Get off your bike and roll it backwards. If the chain is that shot, it might also click when you roll it backwards. Since you said it sounded like it was coming from the back of the bike.... that might be a good place to look.

Rcannon · Oct 4, 2002

One idea that drove me nuts on my YZ would be a loose powervalve. Take it apart and service it. I had trouble with mine seperating into two pieces. Why???? Maybe...., and I am no expert,..... it was the piston smacking the side of it. It did not hit hard, but enough to polish the side of the piston. I relieved some clearance from the valve, tightened it, and have not been able to hear the noise again.

TWRT · Oct 4, 2002

Is it possible that it is the pipe vibrating where it joins the cylinder exhaust outlet? I use high-temp silicon to seal and quiet it on my 93 WR 250. Try putting your boot against the pipe when it is making the noise to see if the sound changes.

yam 3 · Oct 4, 2002

I had the same problem with detonation on the same model bike. I tried to jet it away to no avail. The round slide carb on that model has few options when it comes to needles. One guy told me to replace the carb with a tmx and jet accordingly and the problem would go away. I did not do it though. Rod blew apart had to resleeve(never do that again) Would have been better to replate. Ping got even worse with sleeve.

Bike sounds like a can of marbles!

MilkJuGGz

Rich Rohrich

Moderator / BioHazard

MilkJuGGz

IrishEKU

A General PITA.

Senior KX Rider

Super Power AssClown

MikeT

Rcannon

TWRT

yam 3

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Bike sounds like a can of marbles!

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