Problem with idle / revs returning slowly

[Flash]

Ok guys, my bike was idling fine before my little low speed spill a couple of months ago. I had it sit in my garage for 2 months before getting it back on the road. I have since replaced the choke cable and throttle cable (unrelated to accident), but I seem to have 2 new problems I can't figure out:

1) when I blip the throttle the revs return to idle rather slowly. I'm guessing maybe 1K every 1/2 to 1 second (not always consistent). I can't recollect, but shouldn't it return faster than that?

2) I used to be able to dial in the idle screw after warming up the bike properly and not having to worry about it for a while. I could actually see the revs increase or decrease in real time as I slowly turned the idle screw. Now, the bike just does not want to idle properly or consistently (even after a 25 minute highway ride). When I try to turn the idle screw it does not react right away and I ultimately end up over-idling it to 3 or 4K and have to dial it back down.


The only other things that might have some bearing is I removed all the vacuum hoses and put a direct fuel line to the carbs and there is a slight oil leak from the top of the right crankcase cover.

Anybody have similar experiences or suggestions?

[conradvr]

Did you block off the vacuum hose connection on the carbs?  Sounds like a too lean problem.

Cheers
Conrad

[MarkusN]

Actually it sounds like false air being drawn (which is kind of a "variable lean condition", and which would also be the case if the vacuum port was left open.) Check also if the intake manifolds are tight.

[mp183]

I had a similar problem and I re-jetted but that did not solve it.  It turns out that the valves were out of whack.  The idle would be low and I would turn up the idle screw,  I would ride and the thing would shoot up to 3,000 rpms or higher, so I would turn down the screw and the rpms would be too low.  It started up lousy when it was cool outside, like it was starting on one cylinder for about 5 seconds.

[JohNLA]

My bike was behaving the same way before changing my valve shims. After that no problems with the idle.

[richard]

I've experienced that a couple times...

the first time, it was a problem with the valve clearance, and changing out some shims fixed it right up (and gave me about 50% more power in the process, didn't realize how badly it was running)

the second time, it was just the throttle cable on too tight.  adjusted it down, so that there was a little more slack, and no more problems.

[higgimonster]

my bike does the same thing and it is brand new.  it just went in for the 600mi breakin tune-up and it will still act funny.

After riding around town for a while when I pull up to a stop the engine will sitt around 3k unless I use the clutch to slow down the speed to 1.5k where it will stay.  It just seems to loose revs very slowly.  Being brand new I doubt it has anything to do with vacuum lines or shims.  Any other Ideas (the dealer said he put som shims in when they serviced it a month ago.

[TheMasterRat]

Interesting.... That sounds exactly like what my bike is doing... I'm guessing it's the throttle cable, but I guess I'll have check the valve clearances as well now....

What's the valve clearance supposed to be on a stock GS500E ( 1989 w/17k miles )?

[Flash]

I did cap the vacuum hose connection. I will double check my intake manifolds and give my throttle cable just a bit more slack to see if that helps. If that does not help, then I guess I will learn how to check my valve clearances for once.

Thanks for the suggestions guys.

[Kerry]

What's the valve clearance supposed to be on a stock GS500E ( 1989 w/17k miles )?

Maybe I can answer several questions all at once.

Here's the Valve Shim Selection Chart from the Haynes manual.

EDIT: Changed link from sisna.com to bbburma.net

[TheMasterRat]

What's the valve clearance supposed to be on a stock GS500E ( 1989 w/17k miles )?

Maybe I can answer several questions all at once.

Here's the Valve Shim Selection Chart from the Haynes manual.

Ok, maybe I'm doing this wrong ( yes, I know I should have a manual ) but on my Seca, valve clearance was measured by turning the crank until the camshaft lobe is pointing up ( small end up ) and putting the feel between the bottom ( big end end ) of the lobe and the valve..

Is it taken differently on the GS500s because NONE of my feelers will slide all the way under, and I've got .004 and up to .027...

Ideas?

Answer : I'm a moron sometimes... My feeler gauges large numbers are in CM or IN... The small ones are mm in which case I have .102 to .686....

Is the GS500 *that* tight?

-edit it again sam-

Judging by the chart and the fact that my feeler gauge's smallest .102 - .152 gauge doesn't fit under the lobe..., is it semi-safe to assume that I'm nearly in the right range for correct clearance on the chart?

[Kerry]

Yep, the GS500 is that tight.

A .001" feeler blade would be .0254mm thick, so actually a little TOO thin.  A .0015" blade would be .0381mm thick, so a little too thick for the lower end of the range.

Here are a few ideas:

1) Get some thinner blades.  See the thread Found a 0.025mm Feeler Gauge online! Woohoo!  An alternative to buying the 20-blade set mentioned in that thread is to buy the individual sizes that you really need (see page 740 of the online kbctools catalog):

Code Select Expand

Thickness         Part Number    Price
=======================================
.001"  (.025mm)    1-957X-K1    $ 3.11
.0015" (.038mm)    1-957X-K1X     1.66
.002"  (.051mm)    1-957X-K2      1.66
.0025" (.064mm)    1-957X-K2X     1.66
.003"  (.076mm)    1-957X-K3      1.66
.004"  (.102mm)    1-957X-K4      1.35
=======================================
                               $11.10

I take it back - buy the set!  

2) Check out the thread Valve Clearances for several good ideas, especially the "no blade" method.  (Rotating the bucket by hand to test for >0 clearance.)

3) Get a too-thin shim for fairly precise measuring with your thicker feeler blades.  See richard's post in the thread 0.000 Valve Clearance?

-----------------------------------------------------

You DO have a micrometer, or dial calipers, or some way to measure your shim thickness, right?  (You don't need one of these tools until the clearance is outside the service range, but once you pop a shim out you need a good way to measure it, so you can consult the Shim Selection Chart for the right replacement shim.)  This Harbor Freight item looks good to me.

Oh, and if you don't have metric feeler blades and a metric micrometer/calipers, get a cheap calculator for the shop:

mm = inches x 25.4

EDIT: Changed link from sisna.com to bbburma.net

[TheMasterRat]

Lots more superb info from Kerry

So.. what you're saying is... don't close it up until I'm 100% sure? If the .015 didn't fit the most it could be off by is, what, one or two sizes? Is that a large difference in how the bike operates?

Also... The container that goes on top of the valve cover... I took it off and it has one brillo-pad look-alike in it. Should there be two?

[Kerry]

If the .015 didn't fit the most it could be off by is, what, one or two sizes? Is that a large difference in how the bike operates?

If you can't rotate the bucket with your fingers or a tiny screwdriver then you don't know HOW tight it is.  (Re?)read Richard's post in that last thread I linked to.  One of his valves was off by 5 sizes!  In other words, we had to drop 5 sizes before we could get any clearance at all.

And yes, one shim size can have a noticeable effect on how the engine runs.

Also... The container that goes on top of the valve cover... I took it off and it has one brillo-pad look-alike in it. Should there be two?

Nope, just one.  Bedded down in the "aft half".


So, were you planning to "glue" the valve cover gasket onto the valve cover before you reinstall?  I used gasket sealent in the groove of the cover (some folks use contact cement?), and NOTHING on the lower mating surface.  It's not a necessity, but if you reassemble without it you'll see why it might be a good idea for next time....

[TheMasterRat]

I have some RTV Sealant... Should be fine, right?

[Kerry]

I'm not familiar with RTV, but this is what I used:



It will probably make more sense as you look at it, but I seem to remember a warning about NOT applying the stuff to the 4 semi-circular sections of the gasket....

EDIT: Changed link from sisna.com to bbburma.net

[stephan]

I certainly don't mean to muddy the waters here but I was experiencing a similar problem.  When I was downshifiting for a stop sign/light my bike would slowly rev down to about 2500-3000 RPM and stay there unless I let the clutch out slighty which forced it back down to the usual 1500 RPM.

The only thing I'd done was replace the handlebars, and the valve clearances had just been checked.  So I took off my tank and sure enough the throttle cable was binding slightly on the top of the engine.  I re-routed the cable and now everything works great.

Just an idea, it sure beats tearing down the engine to check the valves!

[TheMasterRat]

Just an idea, it sure beats tearing down the engine to check the valves!

It's not that bad  :mrgreen:

Of course... I already had the airbox and carbs out....