Higher Elevation Jetting ..Richer/Leaner?

Started by Blake, August 24, 2005, 11:17:27 PM

Previous topic - Next topic

Blake

Hey Everyone,


Finally fired up the vision today (after not riding it nearly all this summer) and took it for a nice brisk ride to go fill up.  Not bad.  I puttered around virginia tech and kept it below 6k and rode pretty well.  one thing i did notice.  the jetting was off.

Main problems:
the slight stumble i had at 3-4k increased a lot.
Idle increased with increase in engine temp.
when getting on the highway and gunning it.  the bike pulls like a horse from 4-7k then randomly stopped accelerating.  extremely bad jetting...

But also remember, i have individual k&n pods on the bike that was jetted pretty well for my home near dc (near sea level) but now im at about 2000ft above sea level.  For the next couple days ill ride it as it is, but definately will get to it this weekend with the AFR meter.

Just from my initial observations im pretty sure its WAY too rich.  Is that how it goes with higher elevations?  the higher up you go, you need to lean it out?  As the jetting for the individual k&n's is almost on id really like to get it as close as possible and let everyone else in on the fun :)


so am i right in thinking that i need to lean it out some?  I'm thinking i'll decrease the airjet by a size and the main jet by 2 (or do 2 and 3 respectively).  As i remember i have the idle jet as max (60 i believe), but then again, im having my personal doubts that i ever changed it from stock.  i'll definately have to take a look at that.


Either way, i'll let you guys know the jetting soon incase anyone else wants to fiddle around with the individual pods.


Blake
"At first it's like a new pair of underware... Frustrating and constrictive.  But then, it kind of grows on you..."

Ron_McCoy

You've got the right idea. You need to get leaner as elevation increases. You're jetting shouldn't change so drastically with only a 2000 ft change. I live where I can ride from 600 ft above sea level up to 9000 ft in about a hour and in that much difference, the only change is some richness or loss of acceleration at high rpm. I'm sure there is a loss in horsepower but throttle response and drivability don't change all that much.  It will definitely be interesting to see what your AFR meter tells you. Keep us posted.

h2olawyer

I'll second what Ron said.  I live @ 5,000 ft, & often get up over 10,000.  My jetting sizes probably won't work for you but they aren't much different than most of the others.  130 Pilot air jets, 122.5 main in front & 125 in the rear.  Am considering going up to 135s for the pilot air jets - just haven't gotten around to it yet.  At higher elevations, I notice the loss of power from idle up to 10K but it is much more noticeable at the upper RPMs.

Went up to Estes Park Wednesday evening - trying to keep up with 2 - yes, 2! GTS 1000s.  The little V did admirably but they didn't have any problems pulling away from me coming out of the corners.  The elevation change was from 5000 ft. to over 8000 before dropping into Estes Park.  That's the elevation range I've had the most experience in & the power drop is hardly noticeable within that zone.

I'd say futz with the pilot air jets first, then do the mains if necessary.  The idea is to get more air flowing into the engine as air density decreases with altitude.  (I know, it's a bit more complex than that but that's the fundamental idea.

Good luck & breathe well!

H2O
If you have an accident on a motorcycle, it's always your fault. Tough call, but it has to be that way. You're in the right, and dead -on a bike. The principle is not to have any accident. If you're involved in an an accident, it's because you did not anticipate. Then, by default, you failed.

Blake

thanks guys,


I think my main problem with the big change in drivability was that the jetting was probabaly pretty off in the first place, and that this thinner air up here pushed it past its limit.  If i remember correctly the main jet was a little rich to begin with (10.1 at acceleration i think) so thats why i suggested kicking it down two sizes and the air jet just one.  Im pretty sure my airjet is somewhere around 135 and main around 155?  something like that.  then again i could be way off. 



Thanks for the help.

Blake
"At first it's like a new pair of underware... Frustrating and constrictive.  But then, it kind of grows on you..."

jasonm.

YOU CANNOT RUN a 155 main. that's bigger than what an SV1000 when they flat track them with carbs on. 130 main on the bigger carb'd '83 is it stock. With K&N set up maybe a 135. Since you are only changing the intake. Maybe  140's with MAC pipes and K&N's.  '82 carbs work very well with 135 pilot airs frt and rear. ALSO the accel pump has a great deal to do with that 10:1 you are seeing while accelerating. YOU have to consider all the circuits of the carb when twisting the gas. Maybe I have 10 times the experience of most...that is where I am coming from.
looks aren't important, if she lets you play by your rules

Blake

#5
Jason,

Im just going by what my wide band AFR meter tells me.  I'll take a look and report back the real numbers, but 155 im pretty sure is right for the main  for my k&n pods and dual 1.5" exhaust.  All i know is im getting very nice flow through this system.   Hopefully tomorrow (friday) ill have a little time after i fix the brakes on my caddy so i can hook the computer up to it and get real numbers (and graphs) for you


As for the 10.1 thats at a 7-8k steady throttle run uphill with no acceleration at about 70-80mph (i think it was), so the accel pump definately isnt taking play into it.  That was one of my main concerns when using the afr meter and laptop logger to rejet.



Blake



"At first it's like a new pair of underware... Frustrating and constrictive.  But then, it kind of grows on you..."

Blake

also..


if i do indeed have 155mains.. as you say its way too big..wouldnt that indicate the carb is too small?  having to kick the jet up that high?  Also.. whats the carb size on a sv1000?  Wouldnt the fuel sucked through the jet at a 155main on a 34mm carb at full throttle be different (near maxed out) than say from a 40mm carb(at same cfm)? I mean, yes the 40mm can pass more air, but the vaccum would be greater (at the same airflow) in the 34mm than the 40mm.   somehow in my sleeplessness this is making sense..but i might have to edit this post tomorrow morning when i take another look at it.  All in all im just trying to learn more, thats all.


Blake
"At first it's like a new pair of underware... Frustrating and constrictive.  But then, it kind of grows on you..."