Weired Idle Problem

[robc]

Morning all,
I've spent a few weeks searching online with no luck. I cannot find a close match to the symptoms on my bike. It is a 2002 single spark 120,000 mile GS which I've had for a long time. The problem started a few months ago and now it's starting to annoy me. The idle speed varies between 1,100 and 900 RPM. It doesn't hunt. If it's not at 1,100 it is at 900. When at 900 it feels like the bike is about to stall but never does. I can fix the issue by lifting the fast idle lever a tad and then all is well again. The problem is apparent regardless of weather, air or bike temperature. The engine will idle at 1,100 for around 30 seconds before dropping to 900. The engine performs as well as it always has and pulls like a train from 1,200rpm to 7,500rpm with no issue at all. No hiccups, coughs or splutters. Perfectly smooth no matter the revs - well, as smooth as an 1150 boxer ever is.

I know I need to refurbish my knocking throttle body but I don't think that could be the cause. I fitted new spark which made no different plugs at the weekend.

I wonder if one or both of the HT leads are degrading but wouldn't that make the bike run rough at all revs? As I said, it doesn't it's just that damned idle speed dropping after 30 seconds.

All wise words will be appreciated.

Regards

Rob C

 

[Steptoe]

Could be the rubber inlet tubes between the throttle body and cylinder head have started to perish - give them a spray of grease to temporarily seal them while idling and see if it makes a difference to the idle speed. Do not over tighten the jubilee clips that are at each end to compensate . Over tightening breaks the seal

 

[tadhgocuilleain]

Would it be something as simple as a worn idle screw? Sometimes it's sitting in the worn bit - 900rpm- and other times is sitting on the unworn bit - 1,100rpm?

EDIT: Steptoe got in before me - ignore what I said.

 

[Galactic Greyhound]

The BBS (Big Brass Screws) in the Throttle Bodies (TB) AND their threaded ports should be cleaned at least once a year.

To do this, screw the BBS fully home and note the number of turns required.

Unscrew the BBS and check the O-ring is OK.

Clean the BBS with Carb Cleaner.

Remove the rubber cap on the TB vacuum take off.

Spray Carb Cleaner into the BBS threaded port until it runs clear from the vacuum take off.

Reverse purge from the vacuum take off.

Do a final purge from the BBS threaded port.

Allow to drain then replace the BBS and screw fully home.

Back off the BBS to the original noted down setting.

Replace the rubber cap on the TB vacuum take off.

Repeat for the other TB.

 

[robc]

All good pointers. Thanks. Now I have something to do at the weekend along with the fitting of a new battery. Whilst I'm at it I might as well give the crusty old tractor a decent service.

I'll post an update once complete.

Regards

Rob C

 

[robc]

Could be the rubber inlet tubes between the throttle body and cylinder head have started to perish - give them a spray of grease to temporarily seal them while idling and see if it makes a difference to the idle speed. Do not over tighten the jubilee clips that are at each end to compensate . Over tightening breaks the seal

Forgive my ignorance but do you mean the fat tubes from the air box to the throttle body? I've just had a quick look and I can't see a pipe running from the throttle body to the cylinder head.

Regards

Rob C

Sent from my XT925 using Tapatalk

 

[duckspeed]

Steptoe's advice is as ever the best and based on huge knowledge and given away for nowt. Pay attention

 

[Nin]

These bits - bolted onto the cylinder head, TB attaches to them.

Sent from my iPhone using Tapatalk

 

[robc]

Steptoe's advice is as ever the best and based on huge knowledge and given away for nowt. Pay attention

know that. I just couldn't work out which bit I was supposed to be looking at.

Regards

Rob C

 

[robc]

These bits - bolted onto the cylinder head, TB attaches to them.

Sent from my iPhone using Tapatalk

Thanks Nin. In my mind I was looking for a narrow rubber pipe.

Regards

Rob C

 

[mspenz]

Good luck

 

[robc]

I think I've fixed the problem.

I did as Steptoe suggested and sprayed the tubes with grease but that had no effect. Turns out I was a bit shy when turning the idle screws. I was doing 1/16th turns at a time originally thinking I needed to be gentle. The other day I did a full half turn each. Bingo! Tickover now at a steady 1,200 ish.

Thanks for all the suggestions.

Regards

RobC