kx250 knocking noise

[kx250-818]

Hey guys I'm a new rider i recently bought a KX250. On my last ride at Dove Springs i was riding my KX250 in 5th gear and i had it pinned for about 4-5min and after this i started hearing a knocking noise in the motor. Might i add that i had to change 2 spark plugs in the last 3 rides. I dont know what this noise can be from its not to loud but notice able and it stays constant. Please help.

[Wizzy214]

 welcome to kxriders.

how new are you to 2-strokes?

how loud is the noise?

start your bike, are you hearing a knocking noise? pull the clutch lever in, did it go away?  if it did go away thats normal. if it didnt might have some bearing failure. and its time for a tear down and some new parts,

[GDubb]

I hope you are exaggerating the 4 - 5 mins part... Deffinitely not good to be pinned WFO in 5th for 4 - 5 mins. Good chance you hurt something.


-G

[kx250-818]

Thanks for the response guys, im a pretty new ridder i have had the bike for about 5months i have never owned any other bikes, and yes i did ride my bike 4-5mins pinned in 5th gear not knowing i cant do this im just becoming familar with dirt bike so i didn't know. say it is a bearing how hard is it to change it im fairly good with tools and my hands i have worked on several cars so i familar with how things run and if it is my bearing what should i do. Also the noise doesn't go away when i clutch and it loud enough to were its noticable. I have also had to change my spark plug 2 in 3rides. Could this have to do anything with it. thanks again. 

[hughes]

Getting the proper service manual for your bike will help you get started. To run a bike pinned in 5th for long periods of time your engine/carb/cooling system would need to be propery tuned for that type of racing or riding. Not uncommon for desert racers to keep them pinned for very long peroids of time but their bikes are set up and tuned for that type of riding.

[Hillclimb#42]

Aren' t you guys missing the obvious here? New to riding and pinned in 5th for 5min. Thats haulin'. Welcome to the site. I've been ridin' a while now and am sure 5th is like new. Don't get there much. I will hold the gas on pinned in second alot though. Cherry red silincers are not unusual. Smoking for 5 minutes after parked is knowing you're riding the thing right.
  Back to the issue, Alot of things can knock. You think its every time the crank turns? Clutch being engaged has no affect? Load on motor have affect? You get the idea. Eliminate what you can. Its not like a rod knocking on a car. Fouling plugs could also be a number of things.
I could ask more and you could add more. You'll put it together sooner or later. Jetted right? floats set? time on the motor since rebuilt? Where did you ride pinned in 5th the highway? You can loosen carbon, no tellin', but don't think your bike can't run pinned. More info for me and the other guys will get better responses from better mechanics too.

[kx250-818]

hey guys yup i was riding back to camp on the highway. Couple of my friends got lazy and didnt want to take the trail back so they took the highway and me being a new rider i didnt want to get lost so i followed. The noise doesnt change with load or with the clutch ingadged. Im almost sure its coming from the motor. I dont know when the last rebuild was they place i bought it from never told me. However this noise was not there until i took that highway ride, and its almost like u can feel the knock when u tuch the motor while its running. 

[CR480R]

My engine makes a knock/rattle sound.. I have a fresh top-end, a brand new rod, crank bearings, etc.... It has done it since i put it together... my buddies low-hour KTM 380 makes a very similar noise...

I think the noise might be caused by the powervalve system... I have rode mine alot and it hasnt gotten any worse. I noticed when I put mine together that the center exhaust valve was pretty loose in its bore.. just an idea..

[Wizzy214]

ugh ugh i think this guy might have a big issue did you hear his bike? im sure the 380 makes alot of racket.  i think im now dumber just reading your reply.

My engine makes a knock/rattle sound.. I have a fresh top-end, a brand new rod, crank bearings, etc.... It has done it since i put it together... my buddies low-hour KTM 380 makes a very similar noise...

I think the noise might be caused by the powervalve system... I have rode mine alot and it hasnt gotten any worse. I noticed when I put mine together that the center exhaust valve was pretty loose in its bore.. just an idea..

[CR480R]

ugh ugh i think this guy might have a big issue did you hear his bike? im sure the 380 makes alot of racket.  i think im now dumber just reading your reply.

Well sorry wizzy. I obviously overlooked this:

However this noise was not there until i took that highway ride, and its almost like u can feel the knock when u tuch the motor while its running. 

[gowen]

For the knocking noise, is it constant while the bike is idling? When you hit the throttle? When the RPMs are coming down? While iding, slowly give it gas and see if the knock is constant with the rpms.

[kx250-818]

Yup the noise stays consistant with the idle and if i trottle it up it goes away but as the rpms are coming back down it starts knocking again. So today im getting ready to take the top end off and take a look inside hopoefully i figure out what its from.

[Hillclimb#42]

Check clutch basket. We have a ktm 85 that we were sure had piston slapping. Made alot of rattling at idle. The rivots that mount the plate to the back of basket was factory rivots which got sloppy. I think kaws are the same. Hinson basket comes with allen bolts, and cured our rattlin' at idle issue.

[kx250-818]

hey guys so so i rebuilt the head on my 250 my first time doing it took acouple of hours but i did it. My old piston had significant side to side movement but no up and down which was the good part. I changed the piston the noise has reduced a lot and so did the vibration, But reading other peoples messages i guess it normal for some kx's to vibrate. anyway thank to those who responded to my post greatly appreciated. 

[Hillclimb#42]

C'mon Wizzy, he means top end. And he also said he just started riding. We all have posted plenty of threads without proof reading. I think Corky rides suzuki's.