Confused and anoyed

[Rake78GS]

I dont understand what is going on with my GS. Here is whats going on:

Last week I went riding with a friend and we spent the day cruzing some coastal and farming roads that surround the area. Almost all SLOW stuff under 60 kph (40mph). While riding the bike was running VERY rough, seemed to be starving for fuel. When starting up after a stop it was hard to start, turned over easy but didnt want to catch.

But after getting back on the highway and running it at 110kph (65mph) or higher for about 15 minutes the bike ran just as good as it always does.

Is this a jetting issue?

[KEITH KRAUSE]

Probably is a jetting issue.
Consider that your bike ran poorly at minimal throttle position (cruising at 40 mph), but ran fine at 65 mph. Main difference here is throttle position and vacuum and the transitioning from pilot circuit to jet needle circuit.
The start up and cruising problems at minimal throttle positions suggest a dirty pilot circuit and/or incorrect jetting/pilot fuel and side air screw adjustments.
The improved performance while opening the throttle more is most likely because you're more into the jet needle now and the increased vacuum will draw fuel easier.

[SqDancerLynn1]

If it runs fine now It may have been a carb needle sticking Maybe flooding one of the carbs... It washed itself clean

[KEITH KRAUSE]

Yes Lynn. Looking at his post in a different perspective, you could say that his bike runs fine now and it was only temporary.
I took it as the bike ran poorly, then ran fine at higher speeds, but would do the same thing again if ridden the same.
Maybe I should look at the glass being half full.

[Rake78GS]

Yes Lynn. Looking at his post in a different perspective, you could say that his bike runs fine now and it was only temporary.
I took it as the bike ran poorly, then ran fine at higher speeds, but would do the same thing again if ridden the same.
Maybe I should look at the glass being half full.

Nope. You were right the first time Keith. This situation always happens. Its just that I rarely ride the slow roads so I tend to forget about it!

So the first suggestion would be to remove the carbs, clean everything, put them back on, and see what happens?

Next step would be new jets?

[KEITH KRAUSE]

Nope. You were right the first time Keith. This situation always happens.
So the first suggestion would be to remove the carbs, clean everything, put them back on, and see what happens?
Next step would be new jets?

Most likely dirty carbs.
Could also be a weak spark problem that improves with higher rpm's. If you have a manual and multi-tester, follow the "Stator papers" here and give your coils/reg/rec a quick check. Stock points system can be a problem. Just a suggestion. I'm thinking carbs but if you have the tester and test info, it's very quick to verify your electrical voltage/resistance and timing is good. Many of us can usually ride the bike and tell the difference between a carb problem and a spark problem, but not always.
I doubt the problem is a failing petcock or vacuum line, only because a failing petcock/cracking line usually gets worse as the demand for fuel increases. The vacuum must over come a spring pressure keeping the diaphragm closed. The compromised/weak vacuum can't pull open the diaphragm completely but will be adequate for lower speeds. But your bike runs better with the increased demand for fuel. But another thing can happen too. Poor vacuum could cause a poor flow at lower speeds/vacuum but rise just enough to open the valve more at higher speeds/vacuum. So it can go both ways. Depends how the diaphragm is damaged. Best way to test if your petcock is operating right is to run the bike on prime. If the problems goes away, your petcock or vacuum line is failing. If any doubt about your vacuum line, replace it because it's cheap.
If indeed carb related, then a good cleaning is probably the cure.
You don't say if the problem was inherited or if the bike just started doing this by itself. If inherited, it could be just incorrect pilot fuel and/or side air screw adjustments. They would have a great effect on lower throttle position/slower speeds. If the screws are adjusted right or the problem just showed up after running fine before, then it's most likely a dirty pilot circuit...unless you have more symptoms than you're saying.
I always suggest replacing the carb manifold o-rings if you remove the carbs. A little more work but it usually needs it. Swap the stock Phillips manifold screws for Allens so you can torque to 6 ft/lb. Coat the new o-rings with high temp bearing grease to help them sit still while assembling and to help them last.
Check and adjust the float levels to .94" too, if needed. It might be a good time to order Robert Barr's VM o-ring kit too, to do a complete job. Just don't actually separate the carbs from the holding bracket/plate. Separating them may reward you with the fuel "T" and two other fuel tubes leaking fuel. You can still clean them well without separating them. You must use high pressure air though to reach into the passages.
You should never need to replace the stock brass jets with new. They should last forever under normal conditions. Just clean them well.

[Jackyl]

Knowledge is a wonderful thing here

Keith has helped me out a lot the last few days, so I got to thinking, he is missing a bit of his tag-line. . . . .

And on the seventh day,after resting from all that he had done,God went for a ride on his GS! (all the way to Keith's house to make sure it was running right)

Thanks again for all the help Keith

[Pharkmeh]

Keith has helped me out a lot the last few days, so I got to thinking, he is missing a bit of his tag-line. . . . .

And on the seventh day,after resting from all that he had done,God went for a ride on his GS! (all the way to Keith's house to make sure it was running right)

Thanks again for all the help Keith

haha - nice tag m8 :-D

[mixongw]

I agree that it's probably a dirty pilot circuit in the carbs. My 1100 would run great as long as I was going fast but wouldn't run for crap going slow. I pulled the pilot jets and cleaned them and the problem went away.

[KEITH KRAUSE]

Keith has helped me out a lot the last few days, so I got to thinking, he is missing a bit of his tag-line. . . . .

And on the seventh day,after resting from all that he had done,God went for a ride on his GS! (all the way to Keith's house to make sure it was running right)

Thanks again for all the help Keith

Ha! God just doesn't have the time to tinker with his GS. And with all the... uh...forgettable things I've done in my life, I certainly owe him some work.
Thanks for the compliment, but all I've done is make some suggestions. You guys have to do the work.

[Rake78GS]

Most likely dirty carbs.
Could also be a weak spark problem that improves with higher rpm's. If you have a manual and multi-tester, follow the "Stator papers" here and give your coils/reg/rec a quick check. Stock points system can be a problem. Just a suggestion. I'm thinking carbs but if you have the tester and test info, it's very quick to verify your electrical voltage/resistance and timing is good. Many of us can usually ride the bike and tell the difference between a carb problem and a spark problem, but not always.
I doubt the problem is a failing petcock or vacuum line, only because a failing petcock/cracking line usually gets worse as the demand for fuel increases. The vacuum must over come a spring pressure keeping the diaphragm closed. The compromised/weak vacuum can't pull open the diaphragm completely but will be adequate for lower speeds. But your bike runs better with the increased demand for fuel. But another thing can happen too. Poor vacuum could cause a poor flow at lower speeds/vacuum but rise just enough to open the valve more at higher speeds/vacuum. So it can go both ways. Depends how the diaphragm is damaged. Best way to test if your petcock is operating right is to run the bike on prime. If the problems goes away, your petcock or vacuum line is failing. If any doubt about your vacuum line, replace it because it's cheap.
If indeed carb related, then a good cleaning is probably the cure.
You don't say if the problem was inherited or if the bike just started doing this by itself. If inherited, it could be just incorrect pilot fuel and/or side air screw adjustments. They would have a great effect on lower throttle position/slower speeds. If the screws are adjusted right or the problem just showed up after running fine before, then it's most likely a dirty pilot circuit...unless you have more symptoms than you're saying.
I always suggest replacing the carb manifold o-rings if you remove the carbs. A little more work but it usually needs it. Swap the stock Phillips manifold screws for Allens so you can torque to 6 ft/lb. Coat the new o-rings with high temp bearing grease to help them sit still while assembling and to help them last.
Check and adjust the float levels to .94" too, if needed. It might be a good time to order Robert Barr's VM o-ring kit too, to do a complete job. Just don't actually separate the carbs from the holding bracket/plate. Separating them may reward you with the fuel "T" and two other fuel tubes leaking fuel. You can still clean them well without separating them. You must use high pressure air though to reach into the passages.
You should never need to replace the stock brass jets with new. They should last forever under normal conditions. Just clean them well.

Thanks Keith! And all the rest who have replied!!
I was thinking carbs, but was hoping for something a little easier......... I have just done the Reg/Rec test from the "Stator Papers" so I know its not electrical. But thanks for pointing that possibility out. Some others may not think of that. Since it DOES run VERY well at higher speed, and since thats where I do 99% of my rideing I think I will put this off till the fall, or at least until after a major Club run in 4 weeks.

I do want to keep my eyes open for another set of carbs. Just so I can get them set up perfectly and just pop them on the bike.

OH! I MIGHT have a lead on an 850GS. Might have some of the parts that I am needing...............

Again thanks to ALL!

[KEITH KRAUSE]

OK. But like I said, if you inherited this problem it could be as simple as proper side air screw adjustments or pilot fuel screw adjustments (underneath). If the bike ran fine at some time with the screws where they are, then screw adjustments aren't the cause/cure.
But if you'd rather wait, let us know later if you need help.