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I just returned from a road trip that took us over some passes a 5000 to 8000 feet. My 2017 T120 does not respond or run very happy at anything over 6000 feet. Is this common? I thought the fuel injection system would adjust to altitude. Lugging at normal RPM constantly having to down shift. Bike had recent 10,000 mile service and runs great under 6000 feet.
 

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You lose power at altitude. IIRC, ~ 35% @ 9,000'. "No air up there". ;) Possibly only a turbo or supercharger could compensate.
 
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My ‘18 T120 was a little stumbly when over 9000 feet but it only has 1000 miles on it at that time. I haven’t returned to that altitude since then but it runs great from -230 ft to 6000 ft.
 

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Fuel injection does indeed compensate for altitude. You'll get the same precise fuel/air mixture as at sea level. Problem is, the air is less dense, so it takes less fuel to make the same mixture. Less fuel and air means reduced power. My wife drives a MINI. I thought its dual turbocharging was overkill until the first time I drove it in the mountains. There's no noticeable reduction in performance at all.
 

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I thought its dual turbocharging was overkill until the first time I drove it in the mountains. There's no noticeable reduction in performance at all.
Yep, turbo and super chargers make their own atmosphere, so the air pressure remains constant as long as you're spooling. I had the same experience driving my GLA45 (turbo'd) Vs my Wrangler (not turbo'd). No loss of power in the GLA.
 

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My 2018 Bonne T120 doesn't like high altitude much either. It's not only down on power, but it kind of stutters when the throttle is on just enough to maintain speed. It was like that completely stock and it's no different since I put a Motone X-pipe, Sleeper Pro slip-ons, and a K&N air filter on it.

It runs fine again once I drop below 5500-6000 ft, though.

Pete
 

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I had two turbocharged bikes back in the day: a 1970 BSA Rocket III and a 1981 Suzuki GS1100. Can't say how either one would have run at high altitude, though. 'Bout the highest elevation they ever ran in was at Irwindale Drag Strip which was around 470'.

Pete

BTW, the BSA was consistently around 0.2 seconds slower at Irwindale than it was at Lions which was around 36' elevation.

rePete
 

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I live at about 5300 feet. My T120 certainly stumbles and surges a little in 1st and occasionally 2nd. I ran up to 10,000 feet with it and it does run a bit worse up there, OK it ran like a slug to be honest. Above 6,000 it gets progressively worse. If I go down to 2,500 feet it runs very nicely.

On my Trophy 1200 TTSE I notice the power tailing off at high altitudes but it still runs cleanly like I would expect, just a bit down on power. I had a Speed Triple and Thunderbird Sport and they behaved like the Trophy. I've had BMWs, R1100RS, K1200 GT and R1200GS over the years. Even a Honda VF1000R. They were all like the Trophy too. Carbs or injection, no matter. It just seems the T120 is a lot more sensitive to altitude and temperature. All the bikes were on stock maps.

I've had the throttle bodies changed on the T120 as the TPS died, and things got a lot better but it is still not perfect in lower gears at low revs under light load. I do have the factory Vince and Hines pea shooters fitted from new. I don't know whether that is a problem or not.

I guess it is how it is and I've learned to live with it. It gets worse the hotter it gets. Over 100F it is worse than on cool days. So for much of the summer it is more noticeable than spring or fall.

Does it bug me, yes. Can I do anything about it, probably not. I just put it down to higher Euro emissions compliance issues. My friends Yamaha mt/z09 seems to have much the same behavior. It is possibly more noticeable on a big capacity twin. I don't know. I hear off idle fueling complaints from those I know who bought 2019 Harley's since Harley stopped selling screaming eagle ECU add-ons.
 

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The higher the altitude the less oxygen there is in the air so the mixture becomes very rich hence the drop in power. You will find on the net a chart showing the percentage of oxygen change per 1000 feet of altitude. To keep the same power you need to adjust the A/F ratio setting, this is what the PCV with AT was designed to do.
 

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The higher the altitude the less oxygen there is in the air so the mixture becomes very rich hence the drop in power. You will find on the net a chart showing the percentage of oxygen change per 1000 feet of altitude. To keep the same power you need to adjust the A/F ratio setting, this is what the PCV with AT was designed to do.
No conventionally aspirated internal combustion engine will achieve the same power output at altitude that it has at sea level regardless of how precise the A/F mixture is. There is simply less air density at altitude and A/F mixture can not compensate for that.
 

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T120 Engine Response at Altitude

Actually I have the same problems as the bike. At 10,000 feet I wheeze pretty badly too. I get headaches and my reactions definitely slow down. My Jag is supercharged and it just storms up there with little perceived loss of power. Loss of coolant and the parts that fall off perhaps, but power not so much. Perhaps a Kawasaki h2 might be a good idea up here in the clouds. Even though I live at over 5,000 feet, I always notice getting above 8,000 feet. But I'm just old.
 
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