Well, after weeks of anguish wondering if the Euro/Aust/NZ/South Africa versions of the WR250F use the same cam timing as the US version (instead of YZ250F timing), I took a punt and retarded the exhaust cam timing one tooth on the WR, at the risk of clipping the exhaust valves with the piston.
Note that the Euro WR already has the famous "grey wire" mod done by the factory. I am running a stock bike with no airbox lid and a YZ400F muffler.
Observations after the first ride are as follows:
- It still has compression, therefore the valves have not collided with the piston (whew).
- It seems a little softer right off the bottom but comes into a noticeably stronger mid range than before, winding out to about the same top end as before. The engine seems to have shifted its emphasis to the mid to upper mid rather than the upper mid to top end. The bike does not need to be revved to oblivion to get the last bit of performance out of it now.
- The exhaust note has more of a "bark" to it now.
- Using an RMX250 reference mule, the bike may be slightly quicker with the YZ timing in a drag race, but it is pretty close.
- I needed to go from 170 to 175 main to maintain the same mixture once YZ timed. Also, the pilot and needle will need to be richened up to restore good throttling.
Am I going to leave it YZ-timed? Yes. The power is much more accessible now in normal enduro conditions, coming in at a lower rev. There appear to be many upsides with no downside. I am very happy.
Please note that the normal Euro muffler may not be free flowing enough for this timing, so a YZ or aftermarket muffler may be required to get the most out of this mod.
If any Euro spec WR owners are thinking of doing this mod and have any questions, feel free to email me.
- Grant
Note that the Euro WR already has the famous "grey wire" mod done by the factory. I am running a stock bike with no airbox lid and a YZ400F muffler.
Observations after the first ride are as follows:
- It still has compression, therefore the valves have not collided with the piston (whew).
- It seems a little softer right off the bottom but comes into a noticeably stronger mid range than before, winding out to about the same top end as before. The engine seems to have shifted its emphasis to the mid to upper mid rather than the upper mid to top end. The bike does not need to be revved to oblivion to get the last bit of performance out of it now.
- The exhaust note has more of a "bark" to it now.
- Using an RMX250 reference mule, the bike may be slightly quicker with the YZ timing in a drag race, but it is pretty close.
- I needed to go from 170 to 175 main to maintain the same mixture once YZ timed. Also, the pilot and needle will need to be richened up to restore good throttling.
Am I going to leave it YZ-timed? Yes. The power is much more accessible now in normal enduro conditions, coming in at a lower rev. There appear to be many upsides with no downside. I am very happy.
Please note that the normal Euro muffler may not be free flowing enough for this timing, so a YZ or aftermarket muffler may be required to get the most out of this mod.
If any Euro spec WR owners are thinking of doing this mod and have any questions, feel free to email me.
- Grant
