Inconsistent idle

[dwvoss]

I've got a GS850L with just under 30K miles. I bought it last year, and have put on about 4000 miles with very little work put into it. My general approach is 'if it isn't broke, don't fix it'.

That being said, I think its time that I look into an idling problem. While it isn't much fun idling .. :-D, I find it beneficial if the bike actually does it well. My problem is that if I adjust the idle to about 1100 when the bike is cold, after it warms up, it will idle at about 3K.

Any suggestions on the most likely cause for this symptom?

[KSP]

It could be you have a vacum leak in your intake manifolds. There are o-rings between the block and manifold and they get hard and crack with age. The manifolds themselves can crack so you might want to replace them as well when doing, checking the orings.

[DimitriT]

This is almost certainly a lean mixture caused by either (as KSP points out) an intake leak, by plugged/dirty jets in the carbs, or by misadjustment of the idle mixture screws or throttles.

You should adjust idle after the bike is fully warmed up, BTW. These bikes don't run right when they're cold. It takes at least 10 minutes of idling for the bike to be fully warmed up (or a couple of miles of riding).

Once its fully warmed up, dial in the idle RPMs. When its cold, use the choke to keep it running. That's what the choke is for.

[doggscube]

Once its fully warmed up, dial in the idle RPMs. When its cold, use the choke to keep it running. That's what the choke is for.

I'm new to motorcycles, and I've been using the choke just on startup. The engine runs for a few seconds, then the revs start to climb, at which point I turn off the choke. I've never ridden with it on, and don't let it warm up very much before heading out. Am I doing it wrong?

Jeff

[dwvoss]

Ok. Sounds like good advice, I was thinking about a potential 'O' ring problem as something that might be variable with the temperature of the engine.

Let me throw out another symptom that may or may not be related. I have now had 3 instances where after pulling a long hill at highway speed, at the top of the hill I start to lose power, and the engine dies. Seems to be a fuel starvation since if I let the bike sit for a couple of minutes, it will start back up as if nothing has happened. I have been able to speed up the restart process by switching to prime and choking. Think this might be the same problem, or something different like petcock or fuel filter?

[DimitriT]

This uphill problem is unrelated to the idle problem.

My guess here is that the carbs are not getting sufficient fuel flow to accomodate the additional draw. There are a few possible culprits.

Tanks cap - makes sure that air can get in. I disassembled mine, cleaned out the small parts, added a little machine oil and put it back together. Pay close attention to how the parts fit together.

Petcock - a rebuild kit is $25 from www.crc2onlinecatalog.com. Once again: Pay close attention to how the parts fit together. Also check the screen attached to the petcock and make sure it isn't clogged.

Carb float valves - I left this for last because its the most work. Check the screens attached to the float valves. Clean the float valves (they may need replacement). Check that the floats are operating correctly and are set to the correct heights.

Some things you can try to isolate the problem: try reproducing the problem with the petcock set to RSV or PRI. If the problem goes away, then its most likely the petcock. Try reproducing the problem with the tank cap off (don't do this on full tank). If the problem goes away, its likely the tank cap.

[dwvoss]

DimitriT, thanks for the tips to try to isolate the problem. Now if I can just reliably reproduce the problem, I should be able to find the culprit.

Dan

[longgreensilverado]

also check your valves. it made a world of difference for me.