Horizons Unlimited, the website for motorcycle travellers.    
in cooperation with
Quality Touring equipment worldwide.
 
Supported expeditions across the globe. Become one of the last true adventurers with Kudu Expedtions!
Navigation
Art
 
Go Back   The HUBB
Search 

Search tips

Air/Fuel Mixture at Altitude for Bing carburetors, as fitted to BMW

from the Bing Agency the best place to get Bing parts in North America) Manual:

"From sea-level to about 3,000 feet elevation, atmospheric pressure decreases about one-inch-per-thousand feet of altitude-therefore our 29.92 barometer reading at sea-level now becomes about 27. At 5,000 feet, about 25, and 20.6 at 10,000 feet. Our engine (and carburetor) only react to air velocity-not weight of air. Not knowing this, the carburetor continues flowing the same amount (by weight) of fuel, and all of a sudden our "ideal mixture" at sea-level becomes extremely rich at higher elevations. The Bing carburetor is less susceptible to changes in elevation than other carburettors in use, and in general does not require jetting changes for the idle and lower part-throttle settings. These settings can be compensated for by mixture screw adjustment. However, the upper part-throttle range will require the lowering of the jet needle to lean out mixture and continuous operation at higher elevation certainly necessitates the changing of the main jet. The table provides all information necesssary to determine jetting changes in relation to altitude changes.

Altitude in feet

Temp (F)

0

1,600

3,300

5,000

6,500

8,200

10,000

11,500

13,000

-22

104

103

101

100

98

97

95

94

93

- 4

103

102

100

99

97

96

95

93

92

+14

102

101

99

98

96

95

94

92

91

+32

101

100

98

97

95

94

93

91

90

+50

100

99

97

96

95

93

92

91

89

+59

100

99

97

96

94

93

92

90

89

+68

100

98

97

95

94

93

91

90

88

+86

99

97

96

94

93

92

90

89

88

+104

98

96

95

94

92

91

90

88

87

+122

97

96

94

93

92

90

89

88

86

 

EXAMPLE: You're going to do a lot of touring in Colorado (Elevation about 5,000 feet). Your machine is performing just fine in Galveston, Texas (Elevation 7 feet). Your main jet is size 150. Temperature in Galveston (86 degrees F)-Denver (50 degrees F). The new jet required to obtain the same mixture ratio as was provided by the size 150 is determined from the equation:

J2= A2/A1 X J1

Where:

A2 = the second altitude (Colorado)
A1 = the first altitude (Galveston)
J1 = original main jet (150)

A2 = 96 (alt 5,000-temp. 50 deg.)
A1 - 99 (alt "0"-temp 86 deg.)
J1 - 150 (original main jet)

J2 =96/99 x 150 or, .97 x 150 = 145

Therefore, the same mixture at sea-level with a 150 main jet will be achieved at 5,000 feet with a 145 main jet (AT ABOVE TEMPERATURES ONLY)

If temperature in Colorado was 86 degrees, we would have:
J2 = 94/99 x 150 = .95 x 150 = 142

When changing jets for altitude, always make correction for temperature as well."

Jump to top

Effect of Altitude on Horsepower,

by Tom Vervaeke

(Doing some research) ..."on the effects of elevation on available horsepower. I did a quick web search and found the following HP calculator.

I did a few runs using the factors below. I only changed the altitude after each calculation.

Constants I used:
----------------
Air Temp: 80 F (median for us in summer)
Barometric Pressure: 29.96 (standard)
Dew Point: 50 F (about normal for Colorado)

Elevation in Feet

Relative HP

0

101.2%

500

99.0%

1000

96.9%

2000

92.8%

3000

88.8%

4000

85.1%

5000

81.4%

6000

78.0%

7000

74.6%

8000

71.4%

9000

68.4%

10000

65.4%

11000

62.6%

12000

59.9%

13000

57.2%

14000

54.7%

So, on average, around town in Denver I've got about 81.4% of the HP someone at sea level would have. On top of Mt. Evans (14,000') you only have about 54.7% of the available HP. Typical mountain riding in the 8000-10,000' range shows us with a 30-35% loss. About what I'd guess. I have no idea on how accurate this calculator is but at a first glance it seems about right.

, Colorado, USA"

Editors note - I think this is roughly valid, ASSUMING that the jetting is corrected for each altitude as well. If you don't change anything and go from properly jetted at sea level straight to 14,000 feet, the loss will be even greater. EFI bikes should be pretty close to this as the injection system should compensate. The R1100GS for instance works quite well at altitude without any changes.

I will try and get around to doing a metric version one day...I promise...

printer friendly version

 



Books
Check out the Books pages for Travel books and videos. Remember if you go to Amazon from our books page, we get a small percentage of every purchase. Thanks! Grant and Susan

Translate page

Who's online
There are currently 22 users and 270 guests online.

Online users

  • Possum
  • GammaGoblin
  • tedmagnum
  • vmabuck
  • peter-denmark
  • bombarde
  • ChrisMurphy
  • Roamer
  • yarglien
  • DarrenM

Discussion

Editors note:
We accept no responsibility for any of the above information in any way whatsoever. You are reminded to do your own research. Any commentary is strictly a personal opinion of the person supplying the information and is not to be construed as an endorsement of any kind.


All times are GMT +1. The time now is 00:24.

Top of page Top Home Shop the Souk Grant & Susans RTW Trip Subscribe to the E-zine HUBB Community Travellers Stories
Trip Planning Books Links Guestbook Search Privacy Policy Advertise on HU

Your comments and questions are welcome. Contact Horizons Unlimited.
All text and photographs are copyright © Grant and Susan Johnson, 1987-, or their respective authors. All Rights Reserved.
Powered by vBulletin® Version 3.6.8
Copyright ©2000 - 2008, Jelsoft Enterprises Ltd.
vB.Sponsors
Search Engine Optimization by vBSEO 3.0.0 RC6