Airheads affected by altitude?

[clonmore1]

Riding my 65 recently on 50+ trips to get some mileage on the newly rebuilt engine and I have noticed an intermittent misfire (I raised this on another thread with some useful suggestions[ch128077]) often not far from home. The bike once warmed up (why do airheads take so long to warm up?) had run well. I have noticed that the misfire happens at roughly the same place, so here is my question - are airhead engines affected by differing altitudes if the change in altitude happens quite quickly?

[wilcom]

are airhead engines affected by differing altitudes if the change in altitude happens quite quickly?

I toured Colorado and mapped out every high pass in the State and went over them.....some were 12,000-14000 ft in elevation, The R65 never missed a beat and I started from Sea Level.

I was down on power at that elevation, but no misses or back fires, just a lil bit sluggish. I was a lil bit down on power at those elevations too 

[Bob_Roller]

As Wilcom has said, the only thing you should notice is loss of power .

I live at 1130 feet, 350 M above sealevel, I used to ride north up to elevations of 7000 feet, about 2400 M, and just saw a significant loss of power, especially on steep grades .

High temperatures will have the same effect, less dense air .

[Barry]

Modest altitudes in the UK are unlikely to be the issue. In any case CV carbs compensate except at idle and full throttle and then the mixture gets richer due to the lower air pressure.

[clonmore1]

Thanks for the replies.

Must be a coincidence that my bike has misfired at roughly the same place on the last two rides (and only there, no where else) I didn't think that the modest elevation changes we have impact on the running of the bike, but worth asking the question.

[wilcom]

my bike has misfired at roughly the same place on the last two rides

Don't ride there anymore!!

Seriously, tell us about the place, twisties? heavy braking?, high speed? any difference other than elevation?
Were you just humming along or was it under acceleration?

If there is no reason for a misfire...... it's only because we haven't found the reason yet.

[Bob_Roller]

Was there anything like a rough section of roadway there ??

Overhead high voltage power lines, the kind that have tall towers ??

[wilcom]

Was there anything like a rough section of roadway there ??

Overhead high voltage power lines, the kind that have tall towers ??

Also was the misfire just losing a beat or 2 or was it a :"kerpow-kerpow-kerpow" of any notable duration?