Elevation Change Question??



7 replies to this topic
  • Sparky_So_Cal

Posted April 08, 2002 - 07:37 AM

#1

I have an 02 yz426 and live in So Cal. The only mod I have done to the bike is a Dubach pipe (don't run the spark arrester insert) and have not done any jetting changes (word on the street is you don't have to locally). I normally ride at saddleback and bike seems to rev out ok,although I don't have anything to compare it to because i haven't ridden any other bike for 12 years. I went up to the Hungry Valley track this weekend and the bike seemed to sputter at the top end and had to do alot of quick shifts. There is a about a 2500 feet difference between the two riding places and was looking for some comparisons from other people. Riding conditions (temp, ect..) was the same at both locations, low 70's. I have never checked my fuel screw, because i thought my bike was running fine. Would the fuel screw affect top end or is that main jet, needdle position?

Thanks in advance
Dave

  • skthom2320

Posted April 08, 2002 - 09:09 PM

#2

oops - double post!

[ April 08, 2002: Message edited by: skthom2320 ]

  • skthom2320

Posted April 08, 2002 - 09:18 PM

#3

There are plots in the back of your manual which show you which jets affect which parts of the the throttle opening.

Pilot is roughly 0-1/8
Needle/clip position is roughly 1/8-3/4
MJ is roughly 1/2-WOT

And you're sure you're not hitting the rev limiter? :)

BTW - best $19.99 I've spent so far was James Dean's jetting guide! Click here ==> jetting guide

[ April 08, 2002: Message edited by: skthom2320 ]

  • SoundChaser

Posted April 08, 2002 - 10:01 AM

#4

Sparky-
I have an `01 and also have the Dubach pipe. I also had not done any jetting changes until about Oct. of last year when the bike was very hard to start( this was also at Hungary Valley). After adjusting the fuel screw with marginal results, I went the jetting route. I ended up with a 45 pilot and 168 main and all the
problems have disappered. You want to consider this. :)

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  • skthom2320

Posted April 08, 2002 - 10:36 AM

#5

. I ended up with a 45 pilot and 168 main and all the
problems have disappered. You want to consider this.


This is interesting. I'm saying go leaner to compensate for altitude and you're saying go richer!

Sparky So Cal - What the heck jets are cheap and you should have at least one step on either side of what you normally use anyway. Try it both ways and let us know how it went!

  • SoundChaser

Posted April 08, 2002 - 12:18 PM

#6

skthom2320-
I didn't necessarily jet for altitude reasons. Personally I don't believe the elevation
change to Hungary Valley is/was that dramatic. It was more geared to the hard starting problems I was facing, probably due to the cooler weather.

I was also experiencing some sputtering on the top-end as well as lot's of poping on decel, which made me go in the direction I went, but normally you're correct in trying to lean out the bike in higher altitude conditions. It just sounded similiar to the same sort of the problems I was having and being that we have the same type of exhaust and the riding conditions sounded familiar, I thought I would offer my 2cents.


Just another note...last year while cruz'n to the Mammoth motocross, I stopped into the Yamaha down in Bishop to request jetting information and they suggested as high as a 178 main. It sounded counter-intuitive, I didn't do it so we will never know. :)

  • Shawn_Mc

Posted April 08, 2002 - 12:36 PM

#7

the problem with the jetting stock is its too lean to begin with. Its not lean enough to hurt anything, but really too lean at least for So Cal sealevel. Ive the same 168 main 45 pilot and the stock needle is 1 notch richer too. But when I bought my bike, it had the 168 in the main to begin with, and ran great. After going to the Thunder Alley pipe, I did the pilot and needle and it go stronger. Id try the 168 main and see what happens. If you havent changed anything else, I would bet your problem will disappear. The main problem is the backfire. Enrichening the carb to relieve this will result in a rich condition. Your backfire on decel is an exhaust leak at the head. :)

  • skthom2320

Posted April 08, 2002 - 02:13 PM

#8

I didn't necessarily jet for altitude reasons. Personally I don't believe the elevation
change to Hungary Valley is/was that dramatic. It was more geared to the hard starting problems I was facing, probably due to the cooler weather.
I was also experiencing some sputtering on the top-end as well as lot's of poping on decel, which made me go in the direction I went, but normally you're correct in trying to lean out the bike in higher altitude conditions. It just sounded similiar to the same sort of the problems I was having and being that we have the same type of exhaust and the riding conditions sounded familiar, I thought I would offer my 2cents.


Duly noted. I wasn't trying to discount your input. Sorry if it sounded like that. I just wanted to make sure that he didn't get confused with the (slightly) conflicting advice by pointing out that jets are cheap and easy to change and there is no really reason why he shouldn't try going richer AND leaner!

How's that for a run-on sentence? :)

[ April 08, 2002: Message edited by: skthom2320 ]





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