1983 GS1100E Strange Sound @ Idle, Help Diagnosing?

[Guest]

Working on getting this bike up to snuff. Relatively new (to me) bike. Full engine rebuild 10k miles ago.

This subtle hiccup at idle has been with the bike since purchase. It doesn't occur when the bike is cold, only after it's heated up. It sounds like a stutter, like there's just a tiny bit of slack in the cam chain or something... As soon is the throttle is off-idle the sound/stutter disappears.

Most audible at 10, 14, 24, and 28/29 seconds:

I haven't opened the top end since purchasing the bike. Starts like a champ every time, idles strong, doesn't need much choke to catch it's stride. I figured the valve clearances were likely solid, but I suppose some clearances could be getting tight causing one of the cam lobes to catch up for a sec...

I recently rebuilt the tensioner with all new gaskets and spring. I re-verified that the plunger is functioning properly.

Put some fresh oil in her since that video was shot and the noise *seems* less frequent. It mostly occurs after she gets to her max operating temp (~200* f)

I have to assume the cam chain or shim clearances are likely out of spec?...

The bike rides like a dream otherwise...

Any insight on what it could be or what to check would be much appreciated.

[azr]

Vacuum leak somewhere that shows up once things heat up?? I'd definitely go in and do you valve clearances if you haven't already since the bikes new to you. Check the cams while you're in there, have a real good look around.

[chef1366]

Sync the carbs and make sure your spark plug caps are good and have a good connection.
Oh and vacuum leaks for sure. /\
/\ /\ /\

[Phaedrus]

Awesome. Thanks for the replies. Will test for leaks, check plug caps and valve clearances, sync the carbs, and do a thorough top end inspection. I'd be pretty stoked if it turned out to be just a tiny vacuum leak... Hopefully it won't be too hard to track it down.

[blowerbike]

i believe the sounds you hear is the starter clutch from the engine running uneven.
look in the boot clamping area for cuts or tears.
if you don't have it....add one..
one you ask?
a nice fat long cable tie to the back bar of the carbs to the frame with a little tension...with no support they bounce and cut the boots.
hell they'll even just fall off sometimes.

[Phaedrus]

i believe the sounds you hear is the starter clutch from the engine running uneven.
look in the boot clamping area for cuts or tears.
if you don't have it....add one..
one you ask?
a nice fat long cable tie to the back bar of the carbs to the frame with a little tension...with no support they bounce and cut the boots.
hell they'll even just fall off sometimes.

Whelp... I inspected for any cracks around the boots today. Couldn't find a thing. Tested at idle with some carb spray. No leaks detected. I did add a cable tie to the carbs. Thanks for that tip--they're awfully heavy to be held up by soft rubber boots...

Went to test ride this eve and there was horrible clattering going on under the valve cover. Warmed up the bike and the noise went away. However, the stutter you see in the vid is now so bad that the bike won't hold idle, it just hiccups to the point that it shuts itself off. She's also gotten progressively harder to start since I've been riding her more...

Time to put her aside until I have the time to dig in and check the top end. I did find a bunch of cracks in a few of my plug caps. I'll probably replace them for good measure while I'm working on her.

[bonanzadave]

I did find a bunch of cracks in a few of my plug caps. I'll probably replace them for good measure while I'm working on her.

BINGO ! That might just solve all your issues. Keep us posted.....

[Phaedrus]

Dug a little deeper today.

Checked valve clearances. All but 3 were well within spec. Cam chain is aligned properly with good tension.

Turns out the PO put aftermarket "Accel Super Coils" (140403) on the bike with 8.8mm plug wires. I ordered a new set of caps and terminals for good measure. I tried reseating all of the boots and terminals, verifying solid connection, but the bike's idle still loped and hiccuped.

I further inspected the carb boots for cracks, but couldn't locate anything suspect. And, now that the bike lopes even when cold I would expect the crack to be fairly obvious...

Sounds like the next step, if these fresh caps/terminals don't fix it, is to do a carb sync. Then, if no go, I might take apart the starter clutch and inspect/repair? I didn't think to mention it before, but when she's cold the starter sometimes makes a loud, high-pitched snapping/pinging sound for the first turn over before the bike sucks enough fuel in to ignite. My GS1000 has never made that noise. I figured it might have to do with the vacuum petcock/fuel intake on the 1100, but maybe it's symptomatic of a failing starter clutch...

[rapidray]

It sounds to me like the idle speed is low. Should be around 1200 rpm.
Ray.

[Phaedrus]

It sounds to me like the idle speed is low. Should be around 1200 rpm.
Ray.

Yeah, that definitely could be contributing. It sits at 900 cold, 1k at operating temp. Might not be fast enough to make the starter clutch happy.

Took the opportunity to a compression test.

1 - 210psi
2 - 220psi
3 - 200psi
4 - 215psi

Decent compression. Starter sounded totally fine/strong without the plugs in... No weird pinging noise. I think that that initial "starter" noise is a cylinder igniting without much fuel in it before the choke fully engages.

Dunno how long the compression has been where it is, so I'll definitely do a new carb sync and raise the idle speed to 1200 while I'm at it.

[JTGS850GL]

Those compression numbers seem a tad too high to me. I'd start by getting the idle speed set a little higher. These bikes tend to sound a little clunky when the idle numbers get too low.