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rough idle

  • Thread starter Thread starter sternavi
  • Start date Start date
S

sternavi

Guest
Hi
After acceleration in neutral the rpm goes back very slowly to idle,
the motor idle rough, gs 1000
Does it happened because air leaking?
avi
 
Sounds like an intake leak. Slow to return idle is a lean condition. Most likely the o-rings in the manifolds or possibly the manifolds themselves.
Be sure the throttle cable(s) are adjusted and lubed correctly first. Test throttle operation for smoothness. If good, try adjusting your side air screws (VM carbs) or mixture screws (CV carbs) using the highest rpm method. If the screws were set way off, it's possible they could be the problem. Of course, if you do have an intake leak, adjusting the screws accurately won't be possible.
Another way to check the screws is to just set them at 1 1/2 to 1 3/4 turns out from lightly seated (VM), or about 1 1/4 turns out for (CV). These general adjustments may not be exact as when adjusting with the bike running, but at these settings it's very doubtful that a slow to return idle is the fault of the screw settings.
I just want you to make sure it's not something simple like cable operation or screw adjustments before you take the carbs off to get to the manifolds.
What year 1000?
 
My bike was idling at about 1000 RPM after initial warm-up. Then, 20 minutes later it would idle at 3000 RPM.
So, I thought - OK, typical "minor" air-leak scenario - discussed a million times on this site and experienced by me on several bikes. So, I'm hunting this air leak for days with no luck. Plugs are all decent color.
Finally, I take the carbs off and I get a surprise - The #2 carb slide is sticking (not sliding all the way down) - then the light-bulb goes on in my head: Too much air going through the carb throat because of a stuck slide will produce a high idle just like a minor air leak would, but still not lean enough to cause the plug to be white.
Anyway, I lightly sanded (2000 grit - very fine) the slide and the body and now all is well.

Regarding the rough idle (when it does finally come down to normal): This is, in many cases, due to uneven compression between cylinders or just downright low compression. Now, low compression is most commonly due to having insufficient valve clearance. Once I adjusted my valve clearance, then my idle smoothed out and the bike ran much better in general. Low compression also leads to difficulty starting.
 
Also don't underestimate the role of carb sync in obtaining a good idle. I had one cylinder so lean at idle after a "bench sync" the you could grab the pipe with your hand.

So, to sum up:
1) Adjust your valves.
2) Check for intake leaks.
3) Clean/rebuild carbs (if necessary), then do a good vacuum sync.

I never knew how good idle could be until I did those things.
 
Yup. Like the others say, you have to do the basic tuning/maintanance if you can first.
And to add to my first post...if the problem just suddenly started and the bike ran fine before, then it wouldn't be related to any mixture/pilot fuel/air screws. They generally don't move by themselves and you'd know if you played with them.
But if you inherited this problem, it could be the screws or any number of things. I mention the screws because it's very easy to check if they're causing a problem and you can always keep a record of their current settings and return them to where they are if you don't like the results.
 
KEITH KRAUSE said:
Sounds like an intake leak. Slow to return idle is a lean condition. Most likely the o-rings in the manifolds or possibly the manifolds themselves.
Be sure the throttle cable(s) are adjusted and lubed correctly first. Test throttle operation for smoothness. If good, try adjusting your side air screws (VM carbs) or mixture screws (CV carbs) using the highest rpm method. If the screws were set way off, it's possible they could be the problem. Of course, if you do have an intake leak, adjusting the screws accurately won't be possible.
Another way to check the screws is to just set them at 1 1/2 to 1 3/4 turns out from lightly seated (VM), or about 1 1/4 turns out for (CV). These general adjustments may not be exact as when adjusting with the bike running, but at these settings it's very doubtful that a slow to return idle is the fault of the screw settings.
I just want you to make sure it's not something simple like cable operation or screw adjustments before you take the carbs off to get to the manifolds.
What year 1000?
Click to expand...

Hi
I bought this bike gs1000 1980 in a bad condition replace the clutch starter,
solder the side cover of the alternator change a lot of screws,
bought 4 carb rep from K&L clean the carb put new manifold O-ring(not original but stand in hot place),
in this state the motor is work very rough
I don't check the timing nor the velves
Avi
 
Avi,

You've got to at least check compression on each cylinder (sounds like you haven't done that yet). You'll only need to check the valve clearances if the compression numbers are problematic.
I know tools are expensive in Israel, so maybe you can borrow a compression tester from a friend, if you don't have one.
Knowing your compression numbers is a must.

B'hatzlacha, Chaver (success to you, friend)

Natan
 
nabrams said:
Avi,
You'll only need to check the valve clearances if the compression numbers are problematic.
Click to expand...
Are you saying that if your compression reads are acceptable, the valve clearances don't need to be checked?
 
I'm thinking of the typical scenario where there's not enough valve clearance, leading to low compression - which will cause poor starting and idling.
But, yes, it is possible that there's too much clearance which won't result in low compression, but is not good either because the valves won't be opening enough - leading to less combustion gases - leading to anemic power. In my experience, however, this is much less common than the "too-little-clearance" scenario.
 
The compression can still test OK if the valve clearances are too tight. As the engine heats up, it will misbehave and run very lean, mimicking the symptoms of an intake leak.

I've seen this firsthand -- just last week, I worked on a friend's bike where the valve clearances were pretty much zero or very close to zero. Compression still looked OK, but the valves were leaky enough to drastically affect the way it ran, especially after the engine heated up.


So first, at check the valve clearances.

Then check the compression.

Then sync the carbs

Then make sure the intake boots are sealed, and make sure the airbox is sealed so that air can only enter where it's supposed to.
 
OK. I just didn't want someone reading this to get the wrong idea.
You can have very good compression and uniform too and still have the valve clearances out of spec. Both tight and loose.
Kind of the same idea some could have that if they don't hear any "ticking" then the valve clearances are probably allright, which simply doesn't work but many put off checking clearances just because things are quiet up there.
 
KEITH KRAUSE said:
OK. I just didn't want someone reading this to get the wrong idea.
You can have very good compression and uniform too and still have the valve clearances out of spec. Both tight and loose.
Kind of the same idea some could have that if they don't hear any "ticking" then the valve clearances are probably allright, which simply doesn't work but many put off checking clearances just because things are quiet up there.
Click to expand...

Absolutely, amen, and ditto.

You can't know until you actually check, and tight valves will silently kill your bike's valves.
 
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