Africa Twin rd04 power loss at high altitude

[mexm123]

Hello guys, me and a buddy are both riding identical at's trough south america. Yesterday we crossed the border from Argentina to Chile at an altitude of 4200 meters to San Pedro de Atacama.
My bike was struggling. Uphill was around 50/60 km/h. My buddy, with the same bike had no big problems. He went up 100 km/h easily.
What could the problem be? Both bikes had their carbs synchronized, air filters blown out and alternators checked just 3 days back. We have not hit any dusty or bumpy roads since then!
As soon as we got closer to San Pedro (altitude of 2400 meters) my bike was running like normal again.

I do have to mention that my bike has always used up more fuel then my friend's bike. About a liter more. It also has little hiccups when idling.

[JanTheMongol]

My 96' Supertenere also lost a lot of power some years ago on the Stelvio Pass(2757 mt). I am pretty sure, that it is just a question of good carburator setup for high altitude.

[Walkabout]

Originally Posted by mexm123

What could the problem be?

No two bikes are the same, even two coming off the same production line one after another of the very same model.
Blueprinting of engines for race purposes is an answer but you won't be interested in that.
Using fuel injected bikes would help them perform in a similar manner, but let's not go there in this thread.

If I had to guess, I would say that the two bikes have different jettings in their carbs and/or the jet needles are set up differently.

[mexm123]

Okay, but how is this possible if the bikes are exactly the same build? The carbs are adjusted the same too..

[mexm123]

Oh shit, sorry Jan. Walkabout made me me realize that maybe the gasneedle could be off. It does make sense.. I guess I'll be spending my time in this desert town checking the needles.

[Walkabout]

How do you know that those two bikes are "identical" to use your first terminology?

Fiddling with bikes is a pre-occupation of many people so I am suggesting that the jets have been changed on one or both of them at some time.

But, now you will tell me that you know the full history of both bikes?

[Walkabout]

Originally Posted by mexm123

I do have to mention that my bike has always used up more fuel then my friend's bike. About a liter more. It also has little hiccups when idling.

Running rich with blackened spark plug(s)??

[mexm123]

It's looking like this. Bit black, bit brownish. Going to ride without air filter for a short while at high altitude to see what happens.

[Walkabout]

Take your pick from Dan's pictures:-

Spark Plugs

[mexm123]

Took my pick, and decided that it was in the OK range. Did some riding higher up without my air filter. Went uphill at 100km h. Don't really want to mess with my carbs right now, so I guess it's best to find a foam filter somewhere? As long as it get's me trough Bolivia..

[SoCal AdvTourer]

mexm123: Hello. I hope you and your AT are doing well. I am interested in learning if you were able to resolve your AT issue regarding loss of power at higher elevations.

Are high altitude jets available from Honda for those who live in higher elevations? Also, is it common for some to adjust their carbs while on the road to accommodate the anticipated passes?

Thanks in advance!

David

(Btw, my RD04 AT did fine at 4300 m at Pikes Peak (Colorado) last fall. I think the dual spark plugs must play a role with maintaining performance at higher elevations... However, my AT stumbles (or hiccups) at idle as well. It dips from approximately 1100 rpms to 750 rpms before recovering. I am not sure of the root cause. It happens regardless of whether the engine is hot or cold.)

[mexm123]

I did not resolve the entire issue. A mechanic in Calama, Chile adjusted the space between the spark plug heads, fiddled around with my air/gasoline mixture screw and cleaned out my air filter. The idle hiccups dissapeared and the bike performed better at high altitude. Still, at 5000m it could not reach more than 30km an hour uphill and offroad but it worked.

I can't say anything about being able to find fitting jets, I always though most of them are universal.
The jet changing on the other is not so common and most people I met with carbs just keep it how it is. If you suddenly go down a few kilometers you dont want to be running with a lean mixture. Rather have a mixture that is too rich and won't screw up your engine. It is a lot of effort to change the jets and the biggest lesson I've learned on the road is: If your bike runs, don't mess with it. I have run in so much trouble because I wanted my bike to run a bit better that it is just not worth it. But that is my opinion.