Howdy all, got a question for the Carb gurus.

I'm helping a friend shop for a new(to him) bike, and he's looking at a few of the older sportbikes that are carbed. He's only owned FI bikes, but he likes the look of the 80's and 90's sportbikes.

My only worry is that i've heard around town that people need to rejet their carbs if they buy the bike at a much lower elevation and then bring it up to Flagstaff (7,000ft). My friend regularly (at least once a month) rides down to longbeach (elevation approx 1), and up the road to the ski resort (elevation approx 11,000 ft).

Will major changes like this cause problems for the older carbed bikes?

 

Yes, the carbureted bikes are going to have some difficulties due to the altitude. If the bike is going to reside at 6500' or higher most of the time it should be rejetted to compensate for the lower density air.

A carbureted bike is going to run richer or leaner if ridden at significantly higher or lower elevations. A fuel injected bike will compensate for these changes and inject more or less fuel accordingly. However, this is not to say the the altitude won't effect a FI bike or car. They won't run rich or lean, but they still will be effected by the less dense air. They will loose power as altitude increases no matter what.

The only way to compensate for the loss of air density is to have some type of forced air induction. This would be either with a turbo charger or super charger. In 1982 Honda made the CX500TC, a FI Turbo charged engine. The magazines tested it in the mountains and it performed beautifully with no discernible loss of power. Ah, but I digress...

 

Thanks!

And that CX does look like one tasty piece of bike. Wonder how hard it is to find one in good condition these days.

 

The CX500TC was a limited production bike with only 2500 produced for the US market. I know this because I purchased one back in 1982 and still own it. It is in need of a complete restoration and a project that I hope to do in the not too distant future. Parts are really hard to come by, and mostly only available on the used market. It is a cool bike. For it's day it was really expensive. When 500cc bikes were selling for $2495, this one listed for $4898. That was what 900's were selling for.