Year, Make, Model

The model covered in this video is the 2009 Yamaha YZ250F. Other years will be identical or very similar. My brother owns a 2006 and same procedure applies.

Symptoms

This YZ250F was experiencing hard to start when hot. One reason why this may be happening is if the valve clearance is out of spec and too tight.

Diagnosis

I found one tight valve during inspection, and the hot start problem did not go away. The hot start issue was due to it running too rich at idle. The pilot jet was one size bigger than stock and the fuel screw ended up one turn out. I replaced pilot jet with stock and fuel screw ended up two turns out. No more hot start issues! See this post for fuel screw adjustment.

Why should you adjust your valves?

Proper valve clearance is important and should be performed as regular maintenance. Too much clearance and the engine will be noisy and you will effectively lose valve lift. Too tight and the bike may be hard to start. Also, tight valves, as is little to no clearance, will run hotter and may bleed off compression and lead to power loss. When the valve closes, it mates with valve seat in cylinder head to dissipate heat. If it does not close properly, the valves will run hotter.

Valves will wear over time and they “sink” into the head, which means clearances will diminish over time. If you are finding your clearances are diminishing quicker than usual, it is time for a valve job.

I would recommend that you check clearances every 6-8hrs, maybe less often, it all depends on how you ride the bike.

Tools

Torque wrench (I use the ¼” Harbor Freight 2696)
Tapered feeler gauges (these are a must and can be purchased here)

Parts List

The only parts you need are shims, if adjustment is needed. You can buy individual shims (7.48mm) from Rocky MTN here.

How-To Video – Valve Clearance Adjustment

OK, so you used the video above and found some valves out of specification? Below, the full length video is available for purchase. Save yourself some money and take pride in maintaining your own bike!