Back from out west trip - GS acted up a bit!

[stephan]

I just got back from a trip to the Black Hills of SD and highway 550 from Ouray to Durango CO - great trip!  BUT . . . my GS is a bit finicky about higher altitudes.  Here's what happened and maybe someone can explain the technical side of it to me:

When riding at 5-7K RPMs, the bike would lose power, bog down, begin to backfire, and then stall as soon as I pulled in the clutch.  I'd sit there for a few seconds, restart the bike and it would do okay for a few miles, then do it again.  Eventually it stopped doing it, but I could still feel the engine pulsating.  Almost like it was missing every few seconds.  My thoughts were that it was running rich and just got flooded by too much gas and not enough air.  I thought about messing with the carbs, but then decided against it because I don't know enough about the carbs and didn't want to make my situation worse.

Does anyone have any suggestions regarding carb setup?  Is the stock setting best, is there another setting that works better?  I realize that carb setup is a pretty deep subject I'm just trying to make my bike run as effeciently as possible.   :dunno:

[phoenix02]

Pretty dangerous on the highway.  Just for the benefit of others reading your post, my guess is that your petcock is failing.  I did the Honda petcock retrofit to mine and that symptom went away. 

[mr72]

My bike did exactly what you describe and after doing everything under the sun to the carbs, valve adjustment, ignition checks, you name it, I finally took it to a shop.

Initially the shop thought it was leaking float needles in the carbs, so the bike would flood unless you had it revving high enough to use fuel faster than it would leak into the bowls. They changed the float needles and the problem seemed to go away, but the bike plain old died while they were tuning it. Eventually they found that the bike had tons of carbon buildup on the back of the intake valves causing them to leak badly, and I'm patiently waiting for them to finish a top end rebuild.

Their theory on why it would not run right when hot due to the float needles sounded plausible to me. Maybe you should check that? In my case, the bike would not start up again unless I let it "cool" for a while then it would start and run for a few minutes until it started acting up again. I think it was not just cooling off but I also had to wait for it to clear the flooding condition.

Many others reported very similar issues (I researched this...) and the problem in their case was the signal generator. One of the pick-up coils under the right side engine cover may develop a crack in the wire inside that only opens up when the engine is hot, then when you let it cool and it contracts it makes contact again. No idea why this would enable it to run at 5-7K+ rpm though, as it did in my case. But this is also worth checking for you.

Regarding the carbs, read the wiki. Good info there.

[Joolstacho]

If it were the petcock it'd be doing it at all altitudes wouldn't it.
Backfiring -sounds rich to me, due to altitude? what altitude were you at?
What year GS? Mileage?

[sledge]

I will go with that too

If I was running at high altitudes say 3000ft+ for long periods and there were noticeable effects I would consider dropping main and pilot sizes by about 0.95%

[HPP8140]

This is one of many improvements I've noticed with my 02 carbs:

• don't have issues at high altitude
• floats don't shift

[ShowBizWolf]

I love that this thread is from 2004... shows that people are doing searches and really digging through the forum 

Carry on 

[Bluesmudge]

Someone better contact stephan and let him know that we finally solved his problem. Pull that GS out of storage where it has sat since 2004 and fix it!

If anyone was trying to diagnose this problem, I would also check that the carb drain hose is routed properly. If its pointed forward at highway speeds the bike can act kind of like the OP is describing.