Jetting???


2 replies to this topic
  • Dustin_Mabro

Posted November 14, 2005 - 07:40 AM

#1

Let me start out by apologizing :applause: ...

I did a search and couldn't find anything so now i must ask.

I bought an '00 YZ426 yesterday and while i took it for a spin i noticed it didn't really wanna run right....popped a lot on deceleration and wouldn't idle for crap...I'm thinking I need to jet it for the cold weather but i thought i would just ask to make sure it's not something else.

Also the guy who sold it to me said he heard it's bad to pull start these? Is that true or does he just not know what he's talking about?

and also while i've got you're attention how many teeth are you guys running? It is about due for new sprokets so i figured while i was at it i would give it a little more top end...currently it's at a 13 and 42 so i was thinking dropping a tooth in the rear...is 13-42 stock??

Thanks

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  • grayracer513

Posted November 14, 2005 - 09:31 AM

#2

Pooping on decel is caused by either an air leak in the exhaust, or a lean idle mixture, or both. Check the clamps and joints in the pipe and at the head, and then adjust the idle mixture until it idles right, not until the pop goes away. The truth is that they will pop a little when they're exactly right; it's nothing to worry about if it's moderate. If you don't have an extended fuel screw, get one. Running a richer idle mix may fix both your problems if it's getting cold where you are.

Stock gearing is 14/49, a ratio of 3.5:1. Yours, at 13/42, is currently 3.23:1, so it's higher than stock by almost 4 teeth (roughly equals 14/45).

As far as bump starting, no, it isn't bad, but there's a trick to it. Start by putting it in gear and back it up against compression. Then, when your speed is up, hold the compression release in, drop the clutch, and once the engine is turning, ease off the compression release, and EASE on the throttle. It will start right up if it's going to at all. Too quick on the throttle and it will kick back and stall.

If you install the exhaust cam from a YZ450, you can get rid of the compression release and bump start it like a 125 (albeit a very heavy one).

  • Hick

Posted November 14, 2005 - 03:48 PM

#3

I bought an '00 YZ426 yesterday and while i took it for a spin i noticed it didn't really wanna run right....popped a lot on deceleration and wouldn't idle for crap...I'm thinking I need to jet it for the cold weather but i thought i would just ask to make sure it's not something else.

Also the guy who sold it to me said he heard it's bad to pull start these? Is that true or does he just not know what he's talking about?



Yamaha goofed on the jetting for the debut 426, do yourself a favor and buy the standard needle from the '01 426. The stock '00 needle is way too lean just off the pilot, and this contributes to the popping and creates a uniquely bad off-idle throttle response. The '01 needle is the best twelve dollars you could possibly spend on any '00 YZF.

The '00 also benefits from a modded accelerator pump more than probably any model year, do a search on the BK mod on this site.

But learn how to properly adjust the fuel screw (and idle speed) before you do anything else, and as gray said a little popping is normal.


Pull starting this bike will not hurt anyting for any reason I can think of.

Hope this helps.





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