altitude effecting engine function

[Josh]

A question mainly for those living in Coloraodo or living around 6000ft elevation. I have a 79 GS 550 and though I haven't been able to work on the idol issue yet because the rear swing arm is off I was told of a possible reason for my bike idoling at 3000k and figured I might see if anyone had opinions on the issue. A friend and Harley rider mentioned that one possible reason for my bikes high idol may be that the "mixture" may be off for the altitude causing the bike to idol high. Perhaps others can confirm this as a problem and give advice for fixing it.

[chef1366]

Good reading

Read this

http://auto.howstuffworks.com/framed.htm?parent=question377.htm&url=http://204.71.0.3/motoprof/moto/mcycle/carb101/carb101.html

[ddaum]

Read this
http://auto.howstuffworks.com/framed...1/carb101.html

Great link! This should be required reading for all new GSR members!

[Pharkmeh]

Great link! This should be required reading for all new GSR members!

yup - the good stuff just keeps comin

thx\\/

[Josh]

Great link. Thanks. Hopefully this will clear up my problem as I was planning on doing some carb work anyway.

[Basket Case]

Hey! Another GSer from Colorado Springs!

Yup, you'll need to adjust the carbs for high altitude. Keep in mind you'll always be low on HP here... the thin air gives you about 20% less HP here.

[Josh]

So after finally getting the rear swing arm back on I was able to crank her up and adjust the idol which worked until I took the bike for a ride. After it got warmed up it again began tacking out at 3000 at stops. I adjusted the idol twice more with the same effect. I've been told as old as it is the carbs probobly need a cleaning and that this may be due to a compensation by the other carbs (does this make sense, I dont know much about engines). Can anyone think of other possible problems that may be easier then ripping the carbs apart and cleaning them? Also how much time will the carbs take to clean. I do not have a shop to use just a parking space so if it more than a day project I might be SOL. Thanks.

[Ghostgs1]

Josh, I think there may be something else going on. Possibly with the routing of the throtle cables or even a leaking carb boot. Hi altitude will cost you some power and possibly result in a slight change in idle speed, but nothing like you are describing. Do some investigation befor you end up with a biger problem. Ray

[Josh]

Leaking carb boot? Could be the problem. I noticed some fuel dripping out of the nipple on the bottom of the left hand carb after running it yesterday and there is staining on the engine below that carb. It this the problem your describing? What kind of repair does that entail?

[KEITH KRAUSE]

You have the classic intake leak symptom. Air leak. Not fuel dripping.
The classic intake leak...you start up the bike cold and after a minute or so it idles about 1,100 rpm (if you set it correctly). After full warm up, the bike now idles significantly higher. Maybe 1,500 to 3,000 rpm. So you turn down the idle to about 1,100 with the idle adjuster knob and you think all's OK. You shut off the bike and it cools overnight. Next morning the bike won't idle at all (without choke and still maybe not) until you turn up the idle knob again. Bike idles OK. But, the bike warms up and the idle rises up again. Endless cycle.
Try tightening your manifold clamps first and be sure the carbs are seated all the way into their manifolds.
If no joy, inspect the manifolds and manifold o-rings for condition. You'll find the problem there.

[KEITH KRAUSE]

And as for proper idling, at any altitude...
Adjust your side air screws on your VM carbs, using the highest rpm method.
Know how?
But you must FIRST repair the intake leak.
If your manifolds are good, replace the o-rings that rest in a groove cut into the manifolds flat surface that seals the manifold to the head. Apply a coat of high temp bearing grease to the o-rings to help them last. I suggest changing any stock Phillips manifold screws to Allens. Then you can torque them to 6 ft/lb.

[Ghostgs1]

Josh, Keith is a carb guru, I'd trust his advice on the air leaks. You need to address that befor you burn a valve or two. I just read your note that talked about the gas leaking out of the bowl overflow. That is probably a sticky float valve. Could be a misadjusted float also, but in either case it sounds like you need to at least run some carb cleaner thru with your gas. That may be all you need to correct the leak. I think I'd just plan to pull the carbs and get to the bottom of all these little things. If you are carefull you can reuse bowl gaskets, but you might want to get the carb kits and boot o-rings and some carb cleaner (dip type like Berrymans or Gunk). Search here for the VM carb rebuild step by step instructions, someone did a very nice job of the details of the process with detailed photos. It would help a lot. It's really not too difficult of a job but it is a little tiring with all the little parts especially if you are like me and can't see up close real well. All that said, I have no room to talk, after taking mine apart over and over I still need to do it again once more to eliminate a couple of small seeps. It is going to have wait until cold weather, just too busy now and I need to ride. Oh, have you checked out the gsers map? A Great way to find out who is near you for rides and assistance. Ray