Is my bike High?

[FiftyGS1100G]

So I bought this lovely low mileage 82 GS1100G in Denver Co. (the mile high city) in August and on the ride home the pipes are getting bluer and bluer so I'm wondering is thing jetted for one mile high or are these original carbs not susceptible to the effects of altitude? Or is it more likely that things are just plugged up somewhere and this is causing my lean condition. The plugs look fine a nice light tan and are uniform across the bank of cylinders. Any insights greatly appreciated. Ride On! Paul

[Steve]

Stock pipes? Stock airbox? If you are still on your trip, you can do a stop-gap measure and turn the idle mixture adjustment screws out another half turn just to richen up the pilot mixture a bit. When you get to where you have some time to work on it, pull the carbs to check the main jet size. Stock mains are 115. I don't know how much change is necessary for altitude.

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[tkent02]

With CV carbs and the stock intake, they are compensated for elevation changes, very closely. They run just fine around here, up to 14,000 ft. This does not preclude some previous owner from changing to smaller jets because "I got a jet kit for a 650, that'll work",or "that's how we used to do it in the old days", or "Bubba said so" or just because. Regardless, at anywhere near sea level, you need stock jetting, or maybe one size up. Open it up and see what's in there, before something expensive burns up.

[chuckycheese]

Altitude

I don't think altitude is much of an issue. I live at about 1200 feet and have ridden over Donner Summit (which is slightly over 7000 feet) and never noticed any difference in performance, at all. Nobody I've ridden with ever noticed any difference, either.

[BassCliff]

Hi Paul,

Good to hear from you! I see you're still traveling around the country collecting the big GS shafties.

If everything is stock (carbs, jetting, etc), and it's a low-mileage bike, then the pipes are bound to blue up a bit because of the lean settings from the factory. When I got my bike the pipes did the same thing for a while but eventually stopped. Do as Mr. Steve suggests and then when you get a chance you might also want to raise the needles a half a notch or so. If it is not popping badly on deceleration then you're probably not dangerously lean. I wouldn't worry too much.

I hear a product called "Blue Job" works well.

All the best to you and yours,

Cliff

[almarconi]

I would think about a 10% reduction in main jet size would be enough. Don't forget the other carb circuits as well. Probably want to look at needle position, pilot jets and change your mixture screw settings also.

Remember that air density decreases with decreasing pressure and increasing temperature. As your altitude increases, the weight of the air decreases, the fuel quantity remains pretty much the same so your air/fuel ratio becomes richer compared with sea level.

[tkent02]

I would think about a 10% reduction in main jet size would be enough. Don't forget the other carb circuits as well. Probably want to look at needle position, pilot jets and change your mixture screw settings also.

Remember that air density decreases with decreasing pressure and increasing temperature. As your altitude increases, the weight of the air decreases, the fuel quantity remains pretty much the same so your air/fuel ratio becomes richer compared with sea level.

Not true with CVs, they compensate for pressure changes. They do not compensate for density changes, so there is still a leaning out in cold weather. That is not the issue here. He is going to a lower elevation, he needs bigger jets, ONLY if someone previously put in smaller ones.

[almarconi]

Not true with CVs, they compensate for pressure changes. They do not compensate for density changes, so there is still a leaning out in cold weather. That is not the issue here. He is going to a lower elevation, he needs bigger jets, ONLY if someone previously put in smaller ones.

Tom, I am speaking in terms of physical properties not to a specific set of carbs. I think if you review your physical chemistry, you will find that there is a relationship between pressure and density. Regardless of the type of carburetor you have, altitude will have an effect.

[tkent02]

Regardless of the type of carburetor you have, altitude will have an effect.

No, the altitude compensation aspect of the CV carbs was designed to keep a very close to optimum mixture at different elevations, which was necessary to pass emissions regulations, and with the stock intake system it works very well. That is the main advantage of the vacuum operated slide controlling fuel flow, it compensates for pressure changes. It does not open as far or as quickly at higher elevations so that less fuel flows. I ride CV bikes from 5,000 to 14,000 feet with sea level jetting. They run fine, plugs look good all along the way. They are somewhat down on power up high as there is not as much air available to burn, but they run correctly, with a good mixture at all times, good throttle response, good fuel mileage. You can open the throttle all the way without bogging, run it at almost closed throttle without surging, no problems at all. They are not as good as modern fuel injected bikes but they are close. Compared to VMs which run like crap outside of the small elevation window they are tuned for, the CVs are wonderful for those of us who ride at widely varied elevations.