No there is not an 'adjustment' for the higher altitude........
Problem is air/fuel ratio. Very difficult to supply metered gas flow with a fixed orifice and allow for changes in O2 levels.
At higher altitudes (above 5000') air/fuel ratio becomes 'rich'....the higher the richer the mixture becomes.
Short of changing main orifice out to smaller size there is not much that can be done.
Furnace needs more air to get air/fuel ratio back in balance (or less fuel)
Is it time for your medication or mine?
2007 DODGE 3500 QC SRW 5.9L CTD In-Bed 'quiet gen'
2007 HitchHiker II 32.5 UKTG 2000W Xantex Inverter
US NAVY------USS Decatur DDG31