Africa twin altitude problem, any advice appreciated!

[nomadrush]

Hi. I'm curently in Albania exploring the mountain tracks on my africa twin. (it is bloody amaze g by the way )
I am having problems loosing power and running very hot once I get to high altitude of only 1500ft. I've done lots of resirch on blogs and most people manage 2500ft befor they have any power loss.
I will be in Greece soon so I'm sur there will be mechanics and workshops I can use if necessary to sort the problem..
Has anyone got any advice as to what to do, or why my bike is so sensitive?
I have an after Market exaust (Remus) but they recon this should not affect the running.. But they also said they'd never tested it at altitude.
I could remove the airfilter but am doing lots of dusty off roading and have a log long way to go.
Perhaps changing the jets? Any suggestions on what jets??
I saw a post about modifications for africa twins at 4000ft- but may be a bit extream for me and perhaps after these mods it will struggle at sea level?
Anyways, any advice is very. Much appreciated

[AliBaba]

I've no experience with the AT so this is generally for carbed bikes.
As a rough rule of thumb you loose 10% power every 1000m (3000ft) with a healthy engine This means that you should loose approx 5% at 1500 ft, and that's "nothing".

The reason why you loose power is that your air/fuel-mixture gets fatter (less air for the same amount of petrol). As you mention it's possible to remove the airfilter to get more air, but it's usually not smart in the long run.
Another option is to remove the snorkels on the dirty side of the airfilter (if AT have snorkels), or modify the dirty side (drill holes etc).
The other option is to reduce the amount of petrol. You can do this by smaller main-jets and/or drop the needle.

Remember that running fat is not dangerous for the engine, but running lean can be very dangerous. So if you do a modification you have to restore it to original state before you get to a lower elevation.
If you have enough power there is nothing wrong to keep on driving like it is now.


The Remus itself usually make the bike run leaner (which should help you) but it's possible that jets/needleposition where changed at the same time to compensate for this. Maybe it's overcompensated. If the carbs are worn they also make the engine rune rich. Do you have a dyno-kit? They suck.... A dirty airfilter will also make the engine run fatter.

I would have done a testride (a few 100 meters) without the airfilter to see if it gets better.

[nomadrush]

Hi there, don't know your name but big thanks for your reply, very helpful info. The bike is quite jucy at see level- more than the stated mpg in the manual- could this also be a sign that it's running with too much fuel and not enough air on ground level??
Cheers pip

[nomadrush]

Oh yeah- If I changed the needle to run leaner (assuming the last chap had changed it to run fatter when he fitted the Remus) how could I then tell if it was running too lean at sea level? I obviously don't wan to damage the bike and it's alot of work to get to the carbs each time I go up and down.
Thanks again- pip

[AliBaba]

It's not easy to see if the bike runs lean. One way is to read the plugs but with todays petrol this is pretty difficult. It's possible to install an AF-meter on the bike, but that's maybe a bit extreme...


There is no way to make a carbed bike run perfect at all elevations but a good start is that it runs right at sea-level. Best way to do this (especially on a bike with modified exhaust) is to overhaul the carbs and then take a dyno-run where you adjust to get the right air/fuel-ratio. This might involve changing jets.
If the air/fuel-ratio is correct at sea-level you can usually go up to at least 3000 metrers (10.000 ft) without problems, but you will loose power and your idle will decrease.

[Sambor]

I was on my AT over 5000 meters, without any modifocations. But I had such a problem you described. Check if your your choke works properly. Probably you have bad assembled choke cable. Check ecpecially if it is correctly assembled with carburetor.
If your bike consume more than usually you can expect it is problem with choke...

[PanEuropean]

Pip:

I wonder if perhaps your power loss has nothing whatsoever to do with altitude, but instead is caused by carburator icing?

Normally, a change of elevation from sea level to 1,500 feet should result in no detectable difference for a carburetted engine. Heck, if it did make a difference, no-one would be able to drive in Switzerland (or, for that matter, across North America).

At this time of year, outside air temperatures are rather low (perhaps 10 to 15 degrees C) and the air can be quite moist. When cool air is drawn into the venturi of the carburetor, the temperature drops, and ice can form in the carburetor throat. I had this happen to me on several occasions on a VW Beetle. The result is a slow but steady loss of power, and eventually, the engine just sputters out. It might just be coincidental that you are travelling uphill (rising in elevation) as this is happening.

Next time you encounter your 'power loss', see if things return to normal after the engine has been turned off for about 60 to 90 minutes (sufficient time for the residual heat in the engine to melt any ice that may have built up in the carb). In particular, if you have the chance, park the bike in a heated enclosure for a few hours, then start it up and see how it runs. If the problem disappears after either of these two actions, then your problem is carburator ice and not mixture.

This Wikipedia article explains the phenomenon: Carburetor Icing, and this aviation-specific article provides considerably more detail: Carburetor Icing: Part II, Symptoms and Remedies

Note the reference to "temperatures between +5C and +15°C" in the aviation article.


Michael

[dstehouwer]

Maybe not helping you, but does give some information:

We have been driving our Africa Twins offroad this summer in The Alps, up to 3006 meters (9 862.20472 feet according Google ) and they were running fine. So I think something else is wrong, not so much the altitude...

to add to tat, we were driving through the snow sometimes up there.... so also quite cold!

[shandydrinker]

An oldish post I know, 1500ft is not 'high altitude' - even if you meant 1500mtr, the bike should cope fine.

Are the chokes stuck causing overly rich running?

Phil