it will run rich if oxygen density decreases (e.g. going to a higher elevation). it will run lean if oxygen density increases (e.g. going to lower elevation).
atmospheric pressure is the main determinant of oxygen density.
as a *rough* rule of thumb it will run richer by 1% for every 100m increase in altitude. (in the altitude range you will be operating in).
so for you, if you have it perfectly jetted, at sea level it will run about 7% too lean and at 1200m it will run about 5% too rich.
however, even if you never changed altitude, it would be running up to 2% richer or leaner over the entire year due to normal variations in pressure (and temperature and humidity).
I know for sure I would simply try and get it roughly right for where I ride normally, and put up with differing performance at different altitudes as it is a real pain to do any significant re-jetting (i.e. anything more than twiddling the pilot screw).
yes, I agree, it will be hard to tell (otherwise we would have complete forum agreement on jetting?).
but just for reference, I have a lovely WR250F owner manual which has a fair bit of detail on jetting effects. [yes, I know we all have TTR250s here].
so for pure academic interest, that manual says (for appropriate different throttle openings)..
changing WR250F pilot jet from #40 to #38 = up to 6% leaner changing WR250F pilot jet from #40 to #42 = up to 6% richer
moving WR250F needle clip up 1 groove = up to 10% leaner moving WR250F needle clip down 1 groove = up to 10% richer
changing WR250F main jet from #185 to #175 = up to 10% leaner changing WR250F main jet from #185 to #195 = up to 10% richer
of course that is a different carb brand and different state of tune, and who knows what those jet numbers mean in terms of actual flow rate, but maybe it gives some idea of translating elevation related mixture changes (in above post, -7% and +5%) to actual carb settings.
thanks mate very nice info. ill probably never ride by the sea, just wanted to know maximum. you'd be familiar with the blue mountains. i picked the highest place id probably take the bike which is the black ranges through jenolan state forest. 6 foot track to be exact. i would have hated to get there and the bike not run. its so hilly there anyway, the track goes from 1200m to 300m anyway so perhaps my 700m tuned bike will work great out there.........at 700m lol.
yeah that would be great mate. i am a noob at off road though, but im up for a challenge. Im a shift worker though so get every second weekend off, and often have thurdays and fridays off when working weekends.
i have been told that a good ride is from Goulburn to Taralga, (probably best to refill here), then from taralga to wombeyan caves, then on towards berrima, then to canyonleigh, then on to brayton, then to towrang and then back to Goulburn. im keen to try that one soon as its close.
But im up for whatever. dont have my nomad tank yet so range will probably be 200km give or take to be safe. if we keep to that distance before hitting a servo ill be in for sure.
Don't forget ride reports if you do get out there! I was up in the blue mountains at Leura last year for my brothers wedding, he lives down in Sydney now but whilst we were there we went down the coast past Wollongong and up into the southern highlands, which were fantastic. Talking of elevation change, the road up into the highlands was insane! Switchback after hairpin bend after another... I was in a car unfortunately but it would be a lovely road bike run. The forests around looked pretty endless too.
Regards,
Pete
__________________
Pete Brown
Keighley, West Yorkshire
'94 Yamaha TTR 250 Raid (with Open Enduro headlight, grrr...)
Mate, between jobs at the moment, so can do weekdays if that suits your shift work. Otherwise every 2nd weekend for me as well.
Some of the roads I recall you could do on the multistrada let alone the TTR, but a great area for riding. And there are always tracks worth exploring.
Looking at ordering an Acerbis XR tank for extra range - which agree with you, is needed for almost any trip in aus.
Let me know some dates that work for you?
