99 yz400f titanimum valves?

I just bought this bike a couple of days ago. Ive been working on the carb and have it running better. but im still having the same issues with idoling and hot start. Im getting ready to check the valve adjustment. I have been told that if they need adjusted they need replaced. IS THIS TRUE?

I have read suggesting to shim and adjust them which isnt a problem but a tech at the local dealer said if they need adjusted they wont last more than a few days?

:smirk: Would the valves be the reason this thing is so hard to kick over? Once i get it started it run's awsome and seems to have a ton of compression.


Usually if a valve is out of adjustment you can reshim. If the valve clearance stays the same after maybe 15hrs you don't need to replace your valves. If however you do reshim them and the clearances close up in a short period of time then you need to replace them.

Typically tight valves will cause hard starting when the motor is hot.

Is your local dealer a honda dealer? The 99 yz400f did not have titanium valves. You can shim them if they need it. That motor including the valves are typically pretty bulletproof.

The 99 yz400f did not have titanium valves. You can shim them if they need it.
True. They are stainless steel.

You can also shim titanium valves, but usually not more than once.

Even on a stainless valve, shimming more than a couple of shim sizes or having to re-adjust often is a sign of a valve needing replacement.

So would I be better off adjusting these valves to the tighter side of the specks orlooser or middle of the road? Rite now the exaust is. 203mm and the intake is at. 102mm. My book calls for between.15-.20 on the intake and ..25-.30mm on the exaust.

The tighter side. What's interesting is that those are the correct spec's for the 2001 and later bikes. Someone may have set them that way in error.

ive adjusted them and got them within spec now and it is running worse than it did before. Now i cant hardly get it to start or run at all. it started up rite after i got it put back together it ran for about 15 min and when i went to start trying to adjust the idol and fuel mixture and it died and hasnt started since. Ive checked the magnito and coil. the coil is now questionable. The coil is still producing spark but when i check from the orange lead to the black lead it is like it is grounded out. I am also cant get a constint reading on the plug wire itself. Every thing else is checking out. Not sure where to turn from here. I ordered a jet kit from JD, im going to try that and see what happens.

I dont know what else to try or do?

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