DirtRider . Net MX, SX, Arena Cross, Off-Road Community
Dirt Rider . Net Text Version Home
Dirt Bike Dirt Bike Dirt Bike Dirt Bike

This is the text version of DirtRider.Net
Click Here for the Full Version


Pages: 1

crf 250 wont start

(Click here to view the original thread with full colors/images)

Posted by: crack rock---------------------

my buddy has a 2006 crf250r. a few days ago we checked the valve clearances and the exhaust valves were a little tight(.20) on each side. we put smaller shims in and the clearance is now correct. after i put the bike back together it would not start. every7-10 kicks it will fire but wont run. we bump started it in the street and it ran but would not idle. suspecting a timing issue i pulled the small cover on the right side and aligned the two punch marks so that it was tdc the two marks on the cam sprocket appear level with the side of the head like it should be but im not sure. any ideas?


Posted by: bigred455---------------------

You need to check when the intake cam is TDC on the compression stroke. TDC on the compression stroke is when you have the lines on the flywheel at TDC, and the intake lobe will be pointing towards the rear,THIS IS COMPRESSION STROKE. When you have this,you should have the punch mark lined up from the cam to the flat surface of the head. It sounds like your timing is definetly off, from how the bike is sounding.


Posted by: snb73---------------------

Had the same problem on my son's 04 CRF250. Shim the intake valves to spec and it will fire right up. You need to keep both the intake and exhuast vales in spec or you will never be able to start with your foot.

Steve


Posted by: bigred455---------------------

[QUOTE=snb73]Had the same problem on my son's 04 CRF250. Shim the intake valves to spec and it will fire right up. You need to keep both the intake and exhuast vales in spec or you will never be able to start with your foot.

He told us it was done already,correctly I do not know.


Posted by: yz250il---------------------

Hi guys, kinda new here....

So i have a 04 CRF250 i Shimed the intake valves but it wont start at all!

Could i be off by 180 degrees with the timing?, i mean the piston is twice at the top position one time it's compressing fuel and air(all valves are closed) and there is an ignition and the second time it's ejecting the burned fuel out from the cylinder(exhaust valves open).
If I'm right(and i am off by 180 degrees) then there is a spark every time the piston is at the top and the exhaust valves are open ( that would explain the backfire i had when i tried to bump start it).

i guess my question really is, Is there a spark every time the piston is at the top? or only every two cycles .

my second question is can a poor timing cause the valves to hit the piston and damage it or brake?

thanks
Nativ



Posted by: Rich Rohrich---------------------

Quote:
Originally Posted by yz250il

i guess my question really is, Is there a spark every time the piston is at the top? or only every two cycles .

my second question is can a poor timing cause the valves to hit the piston and damage it or brake?


There is a spark every time the piston comes up towards TDC, so one of them is a wasted spark. The cam runs at 1/2 crank speed so the cam position in relationship to TDC is all that matters.

Yes, if you get the cam timing off far enough you can run into clearance issues that will cause the valves and piston to collide.

If you aren't sure if the cam timing is correct, it's best not to try and start it. Pull the cam back out and carefully walk through the re-install procedure outlined in the Honda service manual. If you work slow and carefully it's not too hard. But it is pretty easy to get the cam installed a tooth off. It's important to cycle the engine slowly by hand after you are finished installing the cam and tensioner so you can recheck the cam and crank timing marks and verify they are still in correct time with each other.


Posted by: yz250il---------------------

ok, thanks!

by the way i do have the timing right i fear for the valves and piston cause maybe the first time i had it wrong

i'll check the valvs now...

thanks again


Posted by: yz250il---------------------

Is a faulty throttle position sensor can cause igniting to be late?


Posted by: Impro250---------------------

No when i first got my CRF250 it took my a half hour to start. Its not about kicking hard, its all about kicking when you feel the compression and the more you kick it the easier it will start give it a about a month of riding and it should be starting first kickish =\

(plus they flood easier)



Text Version Home





vBulletin Copyright ©2000 - 2009, Jelsoft Enterprises Limited.
vB Easy Archive Final ©2000 - 2009 - Created by Stefan "Xenon" Kaeser