grain of salt: altitude change tip

[Dark Jedi]

My regular pleasure rides could change as much at 11,000 feet in altitude over the ride. I lived at 4000 feet, but passed over two passes that hit 15,000 feet.

Air is, of course, a problem. I would bog badly at altitude. Adjusting carbs for a halfway point helped, but cruising at 4000 feet caused some fouling.

So....

I went up to the highest point, with a few minor tools. I then drilled holes in the airbox cover. One at a time, and test-rode it some to see the effect.
At 5 holes, it ran well, and stopped bogging. I rode it around a little, and it did not overheat either.

On the way down, I stopped and slapped some gaffer's tape over the cluster of holes to seal them. Best of both worlds!
I have since made a little plastic door with rubber seal that snaps over the holes, and snaps up out of the way when I have it open.
Starving for air? give it more air!

[Hoomgar]

Mechanically controlled cowling instead of a computer chip. =D>

[Guest]

Re: grain of salt: altitude change tip

My regular pleasure rides could change as much at 11,000 feet in altitude over the ride. I lived at 4000 feet, but passed over two passes that hit 15,000 feet.

DANG!! Where do you live? The Alps?

[bwringer]

Nah, you need an automatic airbox de-restrictior automatically controlled by an an actuating arm attached to an elastic air chamber...

In other words, you go up the mountain, your bag of corn chips gets bigger, and a wire duct taped to the bag yanks a door open on your airbox. The process reverses when you go back down the mountain (or eat the corn chips).

We don't need no stinking sensors and computers. All we need is duct tape, snack food, and wire from coat hangers. And maybe a pair of pliers and a rock for a hammer.

[Dark Jedi]

Re: grain of salt: altitude change tip

My regular pleasure rides could change as much at 11,000 feet in altitude over the ride. I lived at 4000 feet, but passed over two passes that hit 15,000 feet.

DANG!! Where do you live? The Alps?

I lived on the plains of Colorado, but preferred to ride over the old passes of the Rockies. Cottonwood was nice, at 12,500, and there are some unpaved ones that go higher. (Unpaved is relative... carved out of granite is technically unpaved...)

[Guest]

Hey darkjedi, Where are you, there are a number of us around Boulder/Denver. How about checking in on the map?http://www.risingconcepts.com/frapper/gsers Ray

[ruddy]

Interesting. I bought my GS850 new in Denver back in 1984. The dealer offered to rejet the carbs, but it ran so well, I declined. The highest I took it was over Loveland Pass (approx 12K ft as I recall), and the bike ran strong all the way. This was with the sealed factory-set pilot screws. Those lean factory settings worked well at a mile plus altitudes and gave me 40+ MPG around town.

[dpep]

This is a great tip. I asked a question about making holes in the air box myslef in the past, but no one reported having actually done it. It seemed to me that an opening in the airbox should be able to compensate for thinner air and you are confirming that it does.

How about posting some pictures of your arrangement? How large are your holes and what is their placement?

[Guest]

Re: grain of salt: altitude change tip

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Starving for air? give it more air!

I'm certainly no expert, but isn't the problem at high altitude a lack of oxygen in the air, not a lack of air itself? Isn't the amount of air the same at all altitudes, just less oxygen in that air at high altitudes?

[bwringer]

Re: grain of salt: altitude change tip

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Starving for air? give it more air!

I'm certainly no expert, but isn't the problem at high altitude a lack of oxygen in the air, not a lack of air itself? Isn't the amount of air the same at all altitudes, just less oxygen in that air at high altitudes?

Nope.

The percentages of all the gasses are the same everywhere on Earth (just under 3/4 nitrogen, about 1/4 oxygen, and very small percentages of other stuff). There's just less air pressure at higher elevations -- one cubic foot contains a lot less air and thus a lot less oxygen at high elevation.

The exact percentages and weights escape me at the moment, but you can find plenty of numbers with a bit of Googling.

The problem is that an intake system designed to move a certain volume of air at sea level can't cope with moving the larger volume of lower pressure air required at high elevations.

There are a couple of pilots around here that might offer up some useful perspectives on high-altutude engine performance.

[gremlin]

my air box has a door on the top, right under the seat. would removing it work the same??

[duaneage]

We live in 79% nitrogen, 20.1 oxygen, and the rest inert gases. At higher altitudes another factor becomes the dew point and moisture level in the air. Typically air is 1 degree celsius cooler every 1000 feet and that affects the results as well.

[SqDancerLynn1]

At the higher alt, the bike will run rich because of the thin air. Opening the air box leans the mixture out some making it run better. Had a 72? Honda 750K
That bike would hardly run at 12K feet

[mixongw]

Nah, you need an automatic airbox de-restrictior automatically controlled by an an actuating arm attached to an elastic air chamber...

In other words, you go up the mountain, your bag of corn chips gets bigger, and a wire duct taped to the bag yanks a door open on your airbox. The process reverses when you go back down the mountain (or eat the corn chips).

We don't need no stinking sensors and computers. All we need is duct tape, snack food, and wire from coat hangers. And maybe a pair of pliers and a rock for a hammer.

Great stuff!

I had a bag of chips explode once in the back seat of my cage. Scared the s*** out of me! That happened on peak to peak highway.