Bike Differences (YZF/WRF)

[MadEarthWorm]

Howdy all,

Can somebody help me understand the main differences (other than weight, lights and a bigger gas tank) between a YZ250F and WR250F or an Offroad bike and a MX bike in general. I read some other threads but I am unfamiliar with the trails scene so the differences are lost on me.

I figure the suspension is not really set up for big MX track jumps on the WR but what else makes it an "Offroad" bike? You can still ride it on a track but is it slower or something? I'm planning on riding my KX250F on some trails btw...

 

[jmics19067]

suspension valved different,electric start,generating system for charging ,wide ratio gearbox,throttle stop,muffler/spark arrestor,odometer drive and an 18" rear wheel are what coes to mind on the WR.

If you where to put YZ cam,throttle stop, and muffler on the WR it would be almost as fast with weight,suspension and I belive ignition mapping holding you back but a heck of a lot cheaper and easier than putting a wide ratio gearbox,electric start,lights and wiring on the YZ

 

[biglou]

Not positive about the 450cc models, but with the 400/426's, exhaust cam timing was retarded one tooth. Other than that, identical valvetrain. Hence the "YZ-Timed" WR's out there. There's plenty of WR's out there that have been YZ-timed, and are running the YZ seat and tank.

 

[Rich Rohrich]

but with the 400/426's, exhaust cam timing was retarded one tooth.

Lou :ohmy: - The WR was advanced one tooth compared to the YZF which opened the exhaust valve about 23 crank degrees sooner than on the YZF. They did this to improve blowdown with the restrictive stock exhaust system that came on the US WRs. Uncorking the exhaust negates any need for the silly WR cam timing, so anyone that changes the exhaust should change the cam timing to YZF spec as well. Same goes for the jetting to a large degree.

 

[SFO]

I used to hate it when my Mom would spank me in public...

 

[Rich Rohrich]

I used to hate it when my Mom would spank me in public...

Lou knows I'm just tugging on the chain he left dangling. :yeehaw:

 

[MadEarthWorm]

Thanks for the info so far. My buddy is getting back into riding (thanx to me) so he won't be modding the bike or anything like that. He loves trails and such but he also wants ride around the track with me so I thought the WR would be a good choice.

 

[biglou]

Doh! :uh:

 

[SFO]

Lou knows I'm just tugging on the chain he left dangling. :yeehaw:

Well I must confess, I also struggle with the advanced~retarded definition too. Just when I think I am advanced I am retarded... :ohmy:

BTW, my WR is decent on a mx track with some clicker adjustments and raising the fork oil level.

 

[jmics19067]

Not positive about the 450cc models, but with the 400/426's, exhaust cam timing was retarded one tooth. Other than that, identical valvetrain. Hence the "YZ-Timed" WR's out there. There's plenty of WR's out there that have been YZ-timed, and are running the YZ seat and tank.

on the earlier yzf/wrfs yes the exhaust cam could just be adjusted 1 tooth . on the later models where they have the auto decompression cams you can't just shift the cam timing or you will throw of the auto decompresion timing and it will be difficult to start if not impoosible to start.

 

[biglou]

Ah! Thanks jmics. Yet another bit of tid that was displaced in my limited memory bank! Advanced, retarded, it's all the same, just move it one tooth and see if it starts! lol (kidding)

FYI-Talk about a wealth of 4stroke info. Rich and SFO prolly taught me, directly and indirectly, at least 75% of what I've learned about these things so far. :thumb:

 

[Dewster]

The WR was advanced one tooth compared to the YZF which opened the exhaust valve about 23 crank degrees sooner than on the YZF.

So you're saying that you would need to advance the timing mechanically by doing this and electronically by cutting the "gray wire"?

 

[Rich Rohrich]

So you're saying that you would need to advance the timing mechanically by doing this and electronically by cutting the "gray wire"?

To run YZF timing using a WR cam on the 400 & 426 engines you need to RETARD the WR exhaust cam timing 1 tooth. The 450s require you to purchase a new cam due to the decompressor mechanism.

The grey wire mod has no specific bearing on the cam timing but most riders who do the cam mod also do the grey wire mod as well.