OK Guys
where do we go with this one ? does it work the same as the enduro stuff ? if the fuel squirt mod a good idea ?

over to the brains

Yes. Change your pump squirt. Also,buy a needle and main jets for your carb.
Your Yamaha parts person can have a needle for you in three days or less. Its an OBEKN. You will need to do search on the KTM board with the key word "OBEKN" to get the yamaha part number and tuning tips for your new jets. With that number you will have a much eaiser time getting your part, dont bother going without it. Also, while your at it get main jets #160,162,&165. You shouldnt need a part number for the main jets. It will be the best bang for the buck you can spend on your 520.
Of coarse I cant take credit for this tip.
Thank you James Dean and Taffy.
I've got some questions for ya Jaffa.
How many links in your chain with 15/40. Is it loose enough to slip in a 45 or so? Have you seen Frank Trott's 520s? Do you know if he has a web site? Many thanks.

http://www.fctrott.co.uk/ is the site you want its ok if you want a kickin forum for SM try www.supermotard.co.uk
not to sure on how many links are in the chain but it wont take a 45 rear for sure

on the mod side i have a full acropavich Ti system so does this make any difference on the jetting ?

Yes it will make a difference in your jetting.
You may want to start with a #168 main jet. Try the OBEKN needle with the clip in 3rd or 2nd slot. The needle OBEKN has a yamaha part #5JN-14916-EN. The yamaha parts fisch is wrong and says that its a different needle but it will say OBEKN on it. Its for a 99 wr 400, the first yr yzf250 and others.
You may also need to adjust your fuel screw for off idle response. Start at 1 3/4 turns out. Only adjust this at 1/4 turn at a time ,its very sensitive.
The easiest way Ive found to access the carb is to remove the two bottem subframe mounting bolts,loosen the two top ones and flip the subframe up onto the handle bars.
Of coarse carb jetting is all trial and error, seat of the pants testing and takes lots of patience. Good luck
If she wont pull 15/40 on top,what gear would you try next? You say you know someone who runs a 5" rear rim. What tire does he have on it?

FC Trott is running 15/42 and thats good for just over 100mph if you read the write you in the 1st SM mag says is a beast in the 1st 4 gears
Quote ...seams less acceleration but if you get in wrong the front fender will try to snap the peak off yer lid           top class

he still runs a 160 gives it a flatter profile
embarresed mode... i cant get to the edge (yet)

  Hello Jaffa, How are you doin'
Just worth noting that the EKN is NOT stock issue for UK WR400(99) the DXM is, so be careful when ordering parts, Did those pic's I mailed you help at all? (Pump Jet Mod)  

I called my friend at the yamaha shop to confirm the info I gave before. He said that the needle I purchased was a #5JG-14916-EN00 and the parts fisch calls it a "EVN needle". When I got it,it was stamped on the needle "OBEKN". Thats the one you want. I paid $13.10US.
I know the # I gave before was different. You probably already figured that out when you did a search for the #. My apology.
Im not sure if the yamaha part numbers are changed from US to UK. I dont think it matters which bike came stock with what needle. As long as you get the correct part you need with the part #. Let us know what you find out.

Guy yes they did help just gathering info before i do it

  Glad they were of use, Jaffa, If you know the Part designation Ie DTM or EKN or whatever, I may well be able to find the Yam part no for you as I have access to the Yam Elec parts catalogue, You shold have my E-Mail addie...drop me a line if I can help  

Hey Guy,
If you have access to a UK yam parts book,could you see if the part #'s are the same between UK & US.
What #'s do you get for a EKN needle & a EVN needle. Thanks

OK Timekeeper, I'll have a look and see what I can find