pipes02

Member
Apr 19, 2001
7
0
I need some help guys. I just finished a topend rebuild of an 03 YZ250 and I am getting a nasty knocking noise. It was knocking a bit before I replaced the piston and rings but now it just worries me. It mainly does it at idle and goes away around a quarter throttle (this is as much throttle as i have given it). The bike has not been started in a couple of months. Am I overlooking something small but big? Is there anyway that I could just have a jet clogged or something, or at worst do I have a bottom end issue. Any advice would be greatly appreciated. Thanks
 

steve125

LIFETIME SPONSOR
Oct 19, 2000
1,252
0
Is it a deep low pitched knock, or a rattle?? does it only knock with throttle and stop when engine is off throttle??
 

pipes02

Member
Apr 19, 2001
7
0
It actually only knocks when it is at idle. It is a deep knock, and also very consistent. I have only let it run for a max of about 10min, and then I would check the plug. The plug seems to be very hot also. It was actually hot to the touch even through motorcycle gloves, which leaves me to believe I may just have a needle jet clogged or something. To be more descriptive the sound is a deep, rattling, consistent knock.
 

bclapham

LIFETIME SPONSOR
Nov 5, 2001
4,340
0
my older 01 yz250 used to knock at slow speed a bit.- i could nver get that thing carburetted right. you need to establish if its detonation/preignition, or a mechanical banging. Maybe take the head off and have a look inside the cyclinder.

i had to replace the powervalve on my YZ- the PV guide can break, a common problem- maybe check its not rattling.

as for the plug being hot to the touch, dont worry about that!
 

Jacob Hansen

Member
Nov 15, 2004
15
0
My `03 CR250 had a knocking sound before i did the top end. I took the top end off, and discovered that the piston had scratch marks, and the cylinder had nicks through the plating. So i bought a complete new top end. Cylinder, piston, rings ect. I putted i back together and guess what................. It`s still making that knocking sound.! Someone told me that is was the clucth knocking when idle. My problem is only at idle, at about quarter throttle there is nothing. i also took the carb completely apart and cleaned it, and re-jetted it for the cold weather. I run 98 octane pump fuel.... I think i`ll just run it.!! :ugg:
 

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