I have searched, but I can't find anything! Wr cam in yz

Ok I bought a, 2001 yz250f basket case. Put it together with all new valves and Springs. And added an wr exhaust cam pn: 003 5um-12180-10-00 12180. My question is the cams timed with the dots flat on the cyl head. The exhaust cam lobes looks like it's one tooth counter clockwise from the way all other cams time. I can pull start it but for the life of me can't kick start it. Did I mess something up? Or is the yz intake cam and the wr cam timed different? Also it won't build any compression on gauge. Like the exhaust cam opening exhaust too soon and long. If you can help me out before I rip it apart to see if I broke a ring putting it together! Thank you!

The Part# you listed for the Exhaust Cam has the auto-decamp mechanism on it.  Any cam that has the auto-decomp is designed to bleed off compression to allow easy kicking/E-start.  So it can't  build more than about 60psi before it bleeds off compression.


As to the timing: the gear is pressed onto the cam and can't be changed by the user.  Yes, they are clocked slightly different from the YZ.

I did not have any problem when I switched the exhaust cam on my 02 YZ.  Its an upgrade going to the 03 that allows easy kicking and you don't have to use the compression release.


I would look for another cause of difficult starting, like carb not adjusted properly: idle adjusted up too high, or fuel screw not set properly.

I know its difficult to adjust if you can't start it.  This is what I do after I clean a carb:


1.  I don't adjust or remove the idle adjustment and I look thru the carb mouth and check for light under the slide.  I just barely want to see light under it.

2.  Once running, I use William1's fuel screw adjustment procedure (search it).  1/4 to 1/8 adjustment can make the difference on both idle and fuel screws!!!! Its ticklish on some bikes.

Thank you, Ron Buell, I think the problem is compression because of the smoke and won't build any compression on gauge, as far as carb it's good I have an ultrasonic cleaner that I used to rebuild carb. It runs really good once pull started but you have to spin it pretty fast to light it off. And it continues to blow blue smoke once I got it going today. About to rip head off

Ah, OK then I assume you did not put a new piston and rings in it or check bore clearance when you re-built it.

Blue smoke is either worn piston / rings or bore; or oil leaking past the valve seals.


You can go a couple of ways with it.  If there is a significant ridge at the top of the bore, then a re-plate the bore and a new stock piston would do it.  If you're wanting an upgrade, then a 262 or 290 cylinder/piston.  Good luck with it.

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