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Auto decomp. on 2001 YZ250F???????


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Any technical types out there been into the 03 top ends yet? My question is could the auto decompression components be installed on the earlier 250F's? If any of you have looked closely at the 03 head you probably noticed that it appears to be the same head from previous years with the comp. release lever hole plugged off. If you noticed the magazine photos over the last few months those bikes actually had all the compression release equipped head with the cable removed and supposedly the auto decomp on them. I saw one of the pre pro bikes at Glen Helen back in June and have been wondering ever since.

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I agree...that would be a mod worth paying for. I have the routine down pat, and have not really had too much trouble starting the bike. In fact, it's kinda funny...I only let my friends that can start it on their own ride my bike ๐Ÿ™‚ Not many end up riding it... Seriously though, I think that mod would be great for early model 250Fs. Maybe we should all start a name list of people who would buy one if Doug Dubach made the mod. He made the handlebar hot start mod...why not an auto decompression mod??

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You guys must have missed my earlier post. Yes the 01's and 02's can get auto decompression.

All you need to do is buy the 03's exhaust cam and timing gear. It's a simple swap out for the 02, and I would assume the 01 as well. I have already pulled my 03's and tested it in my 02, works like a champ. I left the manual in by the way, and both work at the same time.

The 03 still has the mounting boss for the bracket that held the cable on the head, and the hole is plugged with a pressed in cap. So as soon as the parts shop starts showing the cams and stuff for sale I am buying a set for the 02.

We dont typically ride in lakes or cross a lot of rivers with them, but I would thing the wise thing would be to keep the manual for swamping. For those that do that is.

By the way, once you do kick one over with the auto, you will kill for the cam LOL. 4 kicks when flooded will fire it, 1 kick otherwise. And it kicks like a bigbore 2stroke.

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"When you doing it Sunruh? I know you love being out test dummy...LOL

ben"

yer funny ben. har de har har. ๐Ÿ™‚

actually the 96.90 is the entire assembly. the gear is a tolerance fit onto the camshaft. they are one piece when you get them.

when? hmmmmmm. i guess they would have to be available first.

think of this, find a CHEAP new 02, and for (lets say 125) you can throw in the 03 cam and get autodecomp. shweeeeet!

at some point i wonder if i'll have as many original parts on the shelf as i have left on the bike? i'm sure newmann has passed that point already. :D

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YZ250F_Rider/SUnruh,

Can you do a thorough write-up of this procedure (i.e. the auto decomp mod for older models while keeping the decomp lever for swamp situations) and perhaps some pics? This would be great for the 250F FAQ that Rick K. is maintaining (or SUnruh's web-site)...

Much appreciated! Sounds like a really good mod to do once it is proven worthy... ๐Ÿ™‚

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av,

if it REALLY is only an exhaust cam swap, your manual already shows you (with pics) how to do it.

not very hard at all. you should be able to do it completely in 2 to 3 hours.

lets see if i can do it from memory?

1) remove seat and tank

2) pull spark plug wire and plug.

3) remove valve cover

4) losen cam chain adjuster and remove it (might need a new gasket).

5) loosen cam holder bolts and remove it

6) remove old cam and replace with new cam

7) line up the marks and re-assemble.

though i'd kick it over with it all apart to verify it was all done correctly.

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Dunno about the WR's, but I think they have the same cam grind. If so it's just a swap for them as well, as soon as the cams for the 03 YZF's are available.

As far as procedure's, it was easy.

Remove the seat, and tank, and spark plug.

Pop off the vent hoses from the valve cover.

Remove the valve cover.

Spin the engine until the timing dots are aligned.

Remove the chain tensioner.

Remove the exhaust cam.

Reverse the order installing the new cam and gear, pay attention to the timing dots putting the cam in.

Note: On my 02 the 03's cam did not require reshimming for the lifters. Since the cams are dimensionally the same, I am thinking the lifter shims must be for head, and valve length tolerances.

Thats all there is to it. Took me just over an hour total.

The manual and auto do not interfere with each other, (although it did take me a few kicks on the 03 to stop trying to find TDC first, and now I forget to try and find it on the 02 ๐Ÿ™‚). So if you want both, no further mod is needed.

I dont know what to use for the hole plug yet (where the manual goes into the head), as I left the manual on the 02 when I test swapped. I hope by the time the cams are available we can also buy the plug that is used on the 03 as well.

I will try and take pics whenever I get a new cam for the 02, but like SUnruh said it's covered in the manual already. It really is a simple effort.

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