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Old 12-23-2012, 05:52 AM   #1
Failo OP
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Joined: Sep 2006
Location: Buena Vista, CO
Oddometer: 181
Jetting Questions

This isn't a "What size jets should I use?" question, but rather a "Why should I change jets?" question.

I purchased a 950 Adventure with stock jetting and changed to a much leaner set up with FlexJets for my base altitude of 7500' because it seemed to have a little stumble under moderate acceleration and got crappy gas mileage. The bike runs perfectly with this jetting package everywhere from 5000' to 12000'. I can't imagine this thing running any better, and the gas mileage is probably as good as it's going to get, but I'm planning some lower elevation rides (Baja, the midwest, etc) and am wondering what the affects of running this lean jetting will be at the lower elevations. I fiddle with the FlexJets and open them up a little at higher elevations. Can I just close them down a little at lower elevations and be ok?

If anyone has the perfect jetting package for every situation, please throw it out there, but I'm really asking if I really need to go through the brain damage of changing jets for every altitude change. How will the bike run at lower elevations if jetted too lean? Will it run hotter? Will I experience pinging and detonation? Will it damage the engine? Will it just be a minor inconvenience?

I hear stories of guys who can re-jet a 950 Adventure in under 2 hours, but it takes me that long to just get the seat off . What is the down-side to being lazy and leaving my high altitude jetting alone and riding the bike at much lower elevation?

Thanks guys.
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Old 12-23-2012, 06:00 AM   #2
Beastly Adventurer
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Joined: Oct 2008
Location: Athens, Greece
Oddometer: 2,950
maybe you could leave the jetting as it is and restrict a bit the air intake while on lower elevations.
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Old 12-23-2012, 08:50 AM   #3
Hammer Down
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Joined: Sep 2012
Location: Willows Ca
Oddometer: 179
I have a 2 into 1 exhaust with a FMF pipe .Stock air filter and stock jets Bike ran great but on the dyno at 300 elevation bike ran rich.

Now I run a 150/152 main jets and bike runs great.
Ceasar Vasquez
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Old 12-24-2012, 05:28 AM   #4
Sporting Wood
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Joined: Oct 2011
Location: Horneytown, NC
Oddometer: 896
Good tuning works at all altitudes and uses the motor to its fullest potential. Jetting restricted to elevation and restricting air and fuel flow below that which is possible is a pretty good indication its wrong...but. that works for some people.

My bike runs clean from sea level to 14,000', gets high 30's -low forties mpg, makes plenty of grunt too with 180 mains and a free flowing air filter...course admittedly these carbs are a bitch and I've spent the last 6 years figuring them out.

Here's my recipe, all stock except needles and mains.
factory pro needles and the big mains, stock 2nt clip position and 180 mains
lean the floats by 1mm
Screws are at 2 turns, adjust for rpm. Flex jets are great except when they break...mine did.
no air box, just a big foam filter on my homemade baseplate. Aftermarket ones are similar or uni socks would be good too.
I also have Akra's but with the quiet tip.
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Old 12-24-2012, 07:00 AM   #5
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Joined: Jan 2008
Location: Boulder, Co or lost in Mexico....again
Oddometer: 433
I've had 2 950's and never saw a reason to mess with the jetting. Runs perfect with decent milage at any elevation.
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Old 12-24-2012, 09:34 AM   #6
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Joined: Mar 2006
Location: NorthWet Washington
Oddometer: 2,602
You will want to turn the flex jets IN at higher elevation and OUT at lower. But to answer the first question, no, you should not be forced to make the change for lower elevations.... HOWEVER... it will tend to run a little warmer and be a little down on peak power, perhaps pick up a mid RPM hunt/surge, other than that.... I have ran #42 pilot and 138/140 mains at SEA LEVEL, 60deg F and about 50% Rhumidity and bike was fine.. it ran warmer and tended to preignite if lugged.
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