CX500 GL500 650 Global

Does anyone bother adjusting the pilot screws in to lean the fuel/air mixture when riding at elevations above 6500ft (2000meters)? Or does the bike run/start acceptably well running rich? If you do lean them, can you just turn the pilot screws in using the bike tach? The Honda manual has a section (10-4) on high altitude adjustment but it requires a tach that reads in 100 rpm increments. (I don't generally carry one of those in my saddle bag)


1981 CX500 Custom

Just let your spark plugs tell the story,not the theory in the manuals as they won't know what condition the carbs/ignition circuit are in etc.
Keep the plugs the light tan to light brown and you know the mixture is ok.If they are not just adjust by hand to suit.Run a few miles and check again until happy even if you have to do it over a period of a few days.You cannot get a proper colour check on the stand as the carbs/engine need to be warm and the engine to have been put under load

HTH

I was going to post this question, but found this thread instead. So basically throw out what the shop manual says about adjust, set idle, adjust....etc. and go by plug color? Is there any specific way needed to ride, or is it enough to just get the engine warmed up and under way some? Also, I will be changing out engines soon, but can I set my carbs up now, or are they engine specific and setting the pilot screws for one engine won't hold for the other?

All manuals only give a basic starting point on carbs as they know users may have different climatic conditions and states of motorcycle.
On the CX/GLs as you know you screw the mixture screw in all the way but not over tight and then back them out 2.5 turns.Then go for a ride around the block enough to get the temp gauge up and the thermostat to open.Then return home and check the plugs or take tools with you.If too rich turn the screws out another half a turn if too lean screw them in half a turn.
Repeat process until happy allowing for any differences in the sides of the engine.As previously stated I mark the face of the screw with a bit of white emulsion paint when fully screwed in.That way I know to half a turn when I'm at the 2.5 out etc.
This is of course if I can't be bothered to get my Colourtune out which makes the job dead accurate.


http://www.spark-plugs.co.uk/pages/technical/diagnosis.htm

My Haynes has a similar diagnostic chart in it

I have been riding all summer at high elevation. I'm keeping my bike at my Dad's place in Minden, NV (elev.4000) and have ridden as high as 9500 ft with no ill effects. The only thing is the idle rpm needs to be adjusted at the higher levels as it increases. Easy enough to do while sitting on the bike. I have been getting great MPG (50mpg US) and my Iridium plugs look great. The only other issue I have at altitude is a slight brake fluid leak from the reservoir caused by an increase in relative pressure within the reservoir. The only reason it leaks is because I replced the standard Custom bars with Daytona's and the reservoir is now tilted. (I plan to get a new master cylinder this winter.)

Great stuff