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does altitude affect milage? what about power?

chriskarma

chriskarma

my/karma/ranover/my/dogma
Joined
May 14, 2009
Location
Black Rock City/Nevada
Moto(s)
CBR 600 f3
Name
Chris
I moved out of the bay area to near Reno, NV- except I'm about 4000 ft, I noticed when I went over the pass on 80 that I had hardly any power at all, now I do not have to give it full throttle to get up to speed but have lousy mileage.
I drive a 93 CBR 600 f3.

I've been told a bunch of different stuff- A: take off the evap cannister B:re-jet carbs ( both things I have no idea how to do plus not real tools or garage ) C: Change air filter.

I would love to get rid of the evap filter because I like using a floor jack to lift bike to lube the chain and change out the oil. Oh I looked at the filter and it seemed fine ( no dust etc ) .

I used to get around 150 180 miles out of a full tank of gas & now only 75 to 85 miles ( not good out here because sometimes you go 100 miles to the next gas station if you're out exploring back roads.)

Anyone have a knowledgeable opinion?

thank ye!:ride
 
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Yup normal.

Less air density at altitude means there's less air to compress and the power drops off.

Jetting that's correct for lower altitudes results in rich jetting at higher altitudes.

You can try re-jetting the bike for your the altitude with the downside that your bike will be running lean at lower altitudes.

Removing the Evap cannister won't do much of anything except save some weight.
 
Seems like there is something wrong with your bike there. Altitude should certainly reduce power because there isn't as much air available, and a carbed bike will not draw as much fuel as a result. Mileage...I don't know. Your drag is lower so it should be pretty close to a wash. I can tell you from taking my F4 (carb'd) to 10k feet last summer that it was marginally less powerful. I go to over 3k feet all the time and notice no difference at all.
 
I had an F3. Rode over the Sierra Nevadas with it, along with doing some high altitude twisties near there. There was dramatically less power. At the highest point I probably would've topped out at 100mph. Otherwise, what Mototireguy said. If you adjust it for high altitude, it won't be as good at low altitude.
 
TheRiddler said:
I had an F3. Rode over the Sierra Nevadas with it, along with doing some high altitude twisties near there. There was dramatically less power. At the highest point I probably would've topped out at 100mph. Otherwise, what Mototireguy said. If you adjust it for high altitude, it won't be as good at low altitude.
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Weird. I noticed when I was at ~7k feet that I was practically flying everywhere on 395 because the thin air didn't make it feel as fast. I never cruise at 95mph anywhere else.
 
Isn't there more aerodynamic drag at higher altitudes? That would make for a slight drcrease in mileage. Dont think it's much though.
 
Idioteque said:
Isn't there more aerodynamic drag at higher altitudes? That would make for a slight drcrease in mileage. Dont think it's much though.
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There's less drag at altitude. Less air up there. That's why passenger planes fly at 35k feet.
 
Idioteque said:
Isn't there more aerodynamic drag at higher altitudes? That would make for a slight drcrease in mileage. Dont think it's much though.
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Why would there be? The air is less dense, so there should be less drag. Like going through water (very dense) and then moving through air (less dense).
 
Aluisious said:
Weird. I noticed when I was at ~7k feet that I was practically flying everywhere on 395 because the thin air didn't make it feel as fast. I never cruise at 95mph anywhere else.
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Fuel injected bikes do much better at high altitudes. :)
 
Burning1 said:
Fuel injected bikes do much better at high altitudes. :)
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F4 has carbs. But the F4 carbs probably worked better than the F3 carbs. Or maybe the shape of the fairing and how well it funneled air in? :dunno
 
OK, can I simply remove the evap by myself with zero mechanical skill ( except for lube chain change oil ) & any idea how much $$ to re jet the carbs ?
I thought that it was a bit complicated to remove evap can.
 
Step one is to slap a sticker of Calvin pissing all over the word 'Enviornment' on your bike. Seriously, for a street bike, there really isn't a good reason to remove the evap system. Leave it the hell alone, and be happy that we don't have smog checks.
 
If you are willing to do the work yourself, it might be free. Some mechanics are willing to trade jets straight across. Some of these guys have boxes full of jets. At the very least you should be able to find a guy that will help you test different jets before you buy a set. I imagine that the mechanics in Reno are well versed in rejetting bikes. If you buy jets they can be anywhere from $2.50 to about $8 a piece. I would caution against buying a "jet kit" as they are usually close but almost always wrong (kinda like downloading a fuel injection map instead of dyno tuning).

At any rate, it sounds like your bike was probably running fat at sea level, I wouldn't be surprised if a previous owner rejetted before. The stock jetting should be just fine in Reno and should only bog some over hwy80. I've taken plenty of carbed bikes into the mountains and the only ones that ever gave me any trouble were two-strokes.
 
Burning1 said:
Step one is to slap a sticker of Calvin pissing all over the word 'Enviornment' on your bike. Seriously, for a street bike, there really isn't a good reason to remove the evap system. Leave it the hell alone, and be happy that we don't have smog checks.
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No smog for bikes in Nevada, I do have a good reason to remove it-it prevents me from using a jack to swap my oil and lubing chain.

& why should I care about the environment anyway? The earth is always trying to kill ppl with earthquakes and volcano's and the climate is always changing too, last summer here in NV it was real warm and now its freaking cold! Nope when the environment acts like a mature adult I will treat it as one:laughing
 
the grinch said:
If you are willing to do the work yourself, it might be free. Some mechanics are willing to trade jets straight across. Some of these guys have boxes full of jets. At the very least you should be able to find a guy that will help you test different jets before you buy a set. I imagine that the mechanics in Reno are well versed in rejetting bikes. If you buy jets they can be anywhere from $2.50 to about $8 a piece. I would caution against buying a "jet kit" as they are usually close but almost always wrong (kinda like downloading a fuel injection map instead of dyno tuning).

At any rate, it sounds like your bike was probably running fat at sea level, I wouldn't be surprised if a previous owner rejetted before. The stock jetting should be just fine in Reno and should only bog some over hwy80. I've taken plenty of carbed bikes into the mountains and the only ones that ever gave me any trouble were two-strokes.
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your sig line is hilarious:cool

I'm not set up with tools/space to try and figure out jetting - some folks out here insist that I go to the honda dealership to do it but I'm hoping a corner bike shop like a Reno equivalent of O'Hanlons can do it as good but cheaper.
 
Is there a real good reason you use a jack instead of a rear stand? A sport bike is not designed to support its weight with any bits down there. You're liable to dent the exhaust pipes or crack the oil pan or whatever you're using to jack it up.
 
While there are good mechanics that work in mainstream type dealerships, you would be lucky to run across one on accident. I would advise anyone to find a crusty old codger with a few rusty cb's lying in back of his business and a few clean ones in front. And avoid any place with more than three employees unless they service something Italian or German, then it's two employees or less. Including the owner, if the owner doesn't have a wrench in his hand when you walk in, look confused and ask him to direct you to the Walmart, then high-tail it out of there. Nothing worse than a motorcycle shop where the owner wears a clean white shirt.
 
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