Sill knocking

[RM250Rida]

OK, maybe you guys remmber the problem I was having before with the knocking sound. I thought it was form the low octane (89) gas that I was using so I started buying 93. First I tried Coastal's 93 octane. The bike ran a lot better but I still had the knock. The hext time I needed some more gas I got some 93 at a Dandy Mini Mart. Again the bike ran better, even better then it did on coastal, but the knock was still there. I just got done rebuilding my top end and borrowed a little gas from a friend. He mixes the same, uses the same oil but I think his gas is either 93 or 94 that contains oxidants which he buys from Agway. Not sure about where its from but pretty sure it's Agway. I figured the knock was from carbon build up so I thought it;d be gone after I rebuilt it. But tonight after I got it rebuilt and was working on braking it in, I still heard the knock occasionally. It's mainly when I just close the throttle completely from having it anywhere's above 1/2 throttle. I thought maybe the pilot was lean and when I let off and the pilot takes over it wasn;t supplying enough fuel. I played around with the pilot air screw making it richer. The knocks still there and when I let off the throttle a puff of smoke comes out the back so I dont really think it's lean but maybe. I'm begining to think that it may be the power valve slamming shut. I notice when I had the top end apart that if I worked the little lever arm that controls the power valve it will knock if I let right off it and let it shut on it's own. Will it still do that with the engine running? Is there a way to adjust the tension on it so it doesn't slam shut that hard? Or dont you guys think thats the problem?

 

[Brian]

I have this same problem with my KDX, and am stumped? Anyone :think:

 

[JTurn36178]

Is this knock on deceleration only?

When the motor is being pushed by the wheel with the throttle shut?

If that is the situation, then it may sound more like a cluk.

What do you other guys think?

 

[Brian]

Yes, it's under decelleration only, and id definatly a ping/knock.

 

[georgieboy]

Is it just one knock or is it knocking?

 

[nikki]

If the knocking is kind of like a "pinging" noise near the cylinder and on deceleration and you hear it going into a corner when you let off of the gas - it is possible that it's about time for a bottom end. If the bottom end bearing and/or rod is getting worn - the slop will cause this noise. RM250Rida - did you check the play in your rod when you did the new top end?

 

[Brian]

Nikki, this sounds like it may be the ticket, will tear it down soon and inspect it. :)