From Low To High Elevation

[ST1100Y]

Isn't the US spec ST1100 equipped with altitude control?

The EC spec isn't (+ larger jets), hence with lower air-pressure the setting goes rich at altitude.
My ST's where at passes like Col de l'Isèran at 2,770m/9,087ft or Stilfserjoch at 2,758m/9048ft without any issues; a little less agile and not as prompt on the throttle (so a little more consideration when passing a car with two up an luggage), a slightly lower idle (easy to adjust under the tank door), exhaust getting a tad smelly...
OTOH: I'd never set mine too rich to begin with; if one sets the idle screws to like 2 & 3/4 or more turns at sea level, it could end up too rich at altitude, impacting performance badly...

About fuel: lucky if the quality of all the gas over there is so "excellent"...
Over here it just isn't, ST runs like crap on regular, lame on the throttle, range suffers significantly (possible cause you start to wring it more due the decreased performance... I experience the same on the EFI Toyota, which confirms it being related to fuel quality... (BTW same with the VW T6 van: give it premium Diesel and it fires promptly, less valve noise, it pulls smoother plus the range increases by >160km per filling... )
On our 98~100oct premium gas the ST purrs, pulls and gives nearly 100km more on a tank... less ethanol, lower water content, etc...
M2C, FWIW, YMMV...

 

[dwalby]

Interesting info Martin on your experience with higher octane working better in your ST.

I'm with John O. on this one stateside. I've run 87 octane regular on mine since it was new because I tested all the various octane options available when the bike was new and found that I got slightly more range per tankful with 87 octane regular. As I recall in the old e-mail forum days that was pretty much the consensus then.

 

[ST1100Y]

Interesting info Martin on your experience with higher octane working better in your ST.

I don't think it's the octane rating, I think it's the quality...
They can't add much "crap" into premium fuels without significantly messing up the knock resistance... whilst regular can be E10 (or higher), the premium is always E5... fuel at discount stations here is also likely to have a well above standard/average water content...

 

[tt48]

BTDT You may be down a bit on power above 10K’… downshift if necessary. Not to worry.

BTW, there is a carb procedure in the Honda Service Manual if you live and ride above 5K’. Edit: continuous operation above 6,500 ft per the Service Manual… basically just turn the pilot screws out 1/2 turn CW with the Honda special tool.] Not worth the effort if you’re just passing through.

BTW2, make sure the little vent holes in the back side of the panniers are not plugged before venturing on up to altitude.

BTW3, if the gas stations at higher elevations have 85 octane, use it.

John

There are vent holes in the 1100 panniers?

 

[Steve E]

After going up Pikes peak on my old st 1100, blubbering and straining in low gear towards the top, I decided a fuel injected 1300 might be a better choice.
The 11 did okay on Trail Ridge road tho. In the mountains fuel economy improves greatly, along with the joy factor...

 

[Pop-Pop]

I run my 11 with the cheapest gas i can all of the time. Never had a problem. 85 at altitude

 

[Don-STOC237]

The only time I ever had problems at higher altitudes on my ST1100's was when I had put on the extra foam over-filter that comes with the KN air filter. It definitely slows down the airflow enough to starve the engine of air at high altitudes, and had to be removed. And regarding the octane rating of fuel - run whatever is the lowest octane for sale in the region you're riding thru. Often in mountainous areas this is 86 or 85 octane in the USA. Your engine is designed for regular, and runs best on it. If it doesn't, something is wrong with the engine. This is one instance where throwing money away doesn't buy you any advantage, and in fact may lower your economy.

 

[John OoSTerhuis]

BTW2, make sure the little vent holes in the back side of the panniers are not plugged before venturing on up to altitude.

There are vent holes in the 1100 panniers?

Yes, indeed. Back in the old ST1100 email/LiSTserv days, Jeff Bertrand (aka ‘wjbertrand’) STOC 025, famously first reported this little known feature when his panniers’ lids would not open (due to vacuum pressure) after a day trip up to altitude. [note the white grease pencil marks/arrows]

 

[Chris09]

I'm gonna run some lower octane through my carbed bike, see if I get a reduction in exhaust pipe temperature

found this which seems to make my think that at higher altitudes the CV pistons for a given rpm would sit at a lower position to run at the same air velocity, and the tapered needles would throttle the hydraulic end of things and maintain the same air fuel ratio.
Sounds like either the only carb or best carb for varying altitudes outside of maybe the old Q Jet vacuum secondaries is a CV type

Haven't looked at carb stuff for a while, but a couple other things never thought much of, one site indicated that while stoichiometric is 14.7 or 15:1 ]whatever] rich to lean can range anywhere between 12 and 18 on the air side [and still run I guess] another interested thing was enrichment or choke mode can be as rich as 3:1 during the period of atomization but low vaporization. Hey, it must be true, it's on the internet! But give's an idea that even while you may be running smooth as silk during that cold / pre-vaporization phase, there's a lot of wet gas going around. No wonder we added another odd forty percent of milage to bottom end after everything went FI.

On CV (constant velocity) carbs - when the throttle is twisted, the cable opens up the butterfly valve, which allows air to be drawn into the mouth of the carb. You control the butterfly which allows air in, which controls the slides, which controls the air / fuel mixture entering the engine.
Mechanical carbs have the slide directly attached to the throttle cable so your throttle controls how high the slide goes.
Mechanical slide carbs are far more common in high performance situations where the throttle is WO most of the time.
CV, or Constant Velocity carbs offer the best real-world performance for day to day riding where your throttle isn't pinned all the time.
the CV carb allows much more precise metering and thus, a less boggy engine under load conditions. A CV carb lets you twist the throttle wide open and you don't lose power doing this. With your typical mechanical or round slide carb, for example, in a hill climb situation, you twist the throttle wide and what happens is the engine loses vacuum (because it's under a heavy load) and you will lose performance. "Constant Vacuum" carbs have a vacuum tower (the slide and diaphragm assembly) that enables them to detect engine load and make changes to the mixture adjustment accordingly, so you end up being able to accelerate through loads much better. With a faster response.

 

[Slammer]

Pootled up and down the Stelvio at 2800-odd meters without a problem.

 

[Upt' North]

Isn't the US spec ST1100 equipped with altitude control?

The EC spec isn't (+ larger jets), hence with lower air-pressure the setting goes rich at altitude.
My ST's where at passes like Col de l'Isèran at 2,770m/9,087ft or Stilfserjoch at 2,758m/9048ft without any issues; a little less agile and not as prompt on the throttle (so a little more consideration when passing a car with two up an luggage), a slightly lower idle (easy to adjust under the tank door), exhaust getting a tad smelly...
OTOH: I'd never set mine too rich to begin with; if one sets the idle screws to like 2 & 3/4 or more turns at sea level, it could end up too rich at altitude, impacting performance badly...

About fuel: lucky if the quality of all the gas over there is so "excellent"...
Over here it just isn't, ST runs like crap on regular, lame on the throttle, range suffers significantly (possible cause you start to wring it more due the decreased performance... I experience the same on the EFI Toyota, which confirms it being related to fuel quality... (BTW same with the VW T6 van: give it premium Diesel and it fires promptly, less valve noise, it pulls smoother plus the range increases by >160km per filling... )
On our 98~100oct premium gas the ST purrs, pulls and gives nearly 100km more on a tank... less ethanol, lower water content, etc...
M2C, FWIW, YMMV...

Likewise in the UK, it's a different bike on E5 Super. Smoother, sharper, just plain nicer. Plus the benefit of more mpg.

Pootled up and down the Stelvio at 2800-odd meters without a problem.

Likewise again and probably on regular E10. The proof.......picture left.
Upt'North.

 

[tt48]

Yes, indeed. Back in the old ST1100 email/LiSTserv days, Jeff Bertrand (aka ‘wjbertrand’) STOC 025, famously first reported this little known feature when his panniers’ lids would not open (due to vacuum pressure) after a day trip up to altitude. [note the white grease pencil marks/arrows]

That is great info. Thanks, John!

 

[CYYJ]

...for a quick trip to higher elevations (some passes at 10,000ft) do I need to be concerned?

I have never had any difficult with my ST 1100 riding through various passes in Europe. Some of these passes reach 2,700 meters (8,800 feet). So I would say "don't worry" about it. FYI all the tune-ups, etc. on my moto are done in Zurich, about 1,400 foot elevation.

I do suggest that you consider using higher octane (premium) fuel if you are going to be riding mountain roads. Not so much because of the elevation, but because premium fuel delays the onset of detonation (knocking), which will happen if you just happen to be one gear too high coming out of a hairpin turn. If the roads are such that I am constantly shifting & constantly accelerating, I use premium fuel. The rest of the time, I use regular.

Michael

 

[ChucksKLRST]

Never had a problem running up in the High Country with any of my bikes on my Day Rides. And I run Reg Gas. Only a couple of times, my 1979 CB650 going up top of MT Evans. (14264ft) Had to readjust the idle knob about two or three times on the way up. On second thought my old ST1300 would not idle at the top of MT Evans unless I turned it off and then restarted it. Made the trip up fine but would not idle until restated it. I guess it needed time learn where it was in altitude. With that said all my bikes are now Fuel injected. On third thought my DR650 did not want to stay running near the top of Mosquito Pass 4x4 trail(13086ft) Got rid of all my carbureted bikes over the years. Still trying to talk my daughter into sell her little GS500F Suzuki (carbs) and getting a FI machine of some sort.