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OK hear is my question. Right now I am running the stock size jeting with a K&M filter and the Proflow flange. Im around 1000ft where I live and going to be taking a trip to Moab, UT next year to around 6000ft or so. What size is the stock jeting and what size should I go down, oh and brand. I herd that brand matter, sizes are not the same brand to brand. Should I move two sizes or just one, or more? Any help is appreciated.
 

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I've taken mine from 1000 ft to 4000ft, and it ran just fine. If I remember correctly the original size jet is like a 153.8 which is not a common size. They actually come in 150,152, 155, 158,160 and so on. after I added my K&N I went up to a 158 jet, and stil haven't had any [problems
 

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dnhyoung:

Thanks for the help. I have been reading a few things on the internet that people have been saying they have been ok with the stock jetting to around 8,000 with not much power loss. Think if anything I might just jet down one size and see how that goes when I get there and maybe carry a extra one with. Still thinking though...lol Thanks again.

Mike
 

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Just to also let you know of a slight problem that I had with jetting was getting the actual bottom of the carb off. I ended up using an easy-out to remove the 4 corner bolts on the bottom of the carb, and then replace the soft original phillips ones with stainless allen head ones.
 

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For stock 153.8 is correct and that is not a standard Mikuni size. The Mikuni small round jets come in increments of 2.5 with your next larger one from stock being 155 then 157.5, 160 and so on. Most motorcycle shops carry a kit that has most all of the sizes in it and they are only a couple of dollars apiece. On my machine I have the ProFlow adapter with a K&N with the HMF ECO QS1 pipe installed and I am currently running a 155 main jet but will be going up one more size to the 157.5.

I would not think that you would want to go down in jet size the last thing you want to do is lean it our to much, maybe go up a size?
 
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