Highway riding - short hi idle

[RHODESIA SMITH]

Hello Chaps,

This is one of those problems that I have not been able to cure, having done as prescribed for all carb work , orings , valves ect as prescribed on this closely followed forum. (which is great as most times one can't solve every problem by reading out of a typical workshop manual and relying on ones wits only!)

perhaps some of you may have had the same and been able to sort it out.

Bike runs well, I ride on the highway for say approx 100 km ( so it means that it is for a reasonable time frame- not a quick 2min blast), at a reasonably steady speed of around 140km/h ( speed doesn't really play a role here, but high speed- you get the picture) and when I come off the highway at the offramp and pull up to the intersection , the engine idles at about 2000-2500 rpm for about say 5-10 seconds and then settles down to the usual set idle speed of around 1100rpm.
No other concerns.

I have checked for fuel leaks, I have disconnected and blocked off the vacuum line for the fuel tap and ridden it on prime- same thing so its not as if there is some excess fuel in the vacuum line that is getting burnt off. Float level is spot on, sync'd carbs - the works.Fuel consumption is good ( about 14-16km/litre at highway conditions).

doing town riding pull up to a trafic light, idle is fine.

any thoughts?

[Larry D]

No idea what bike you have......but, sounds like it's a bit lean. A hanging idle is a sign of this. Try turning the idle air mixtures screws about an eighth of a turn out, this will richen the idle mixture. If the bike starts to bog at idle, you've gone to far. Make this adjustment in tiny increments and do all the carbs the same amount.

[Nessism]

Hanging idle is one of the most common GS problems. The archives is full of case studies. In order of possible cause: intake boot O-rings leaking, lean pilot circuit, carb sync.

[1948man]

Seems like a lean condition would improve when the bike is really warm and worsen when the bike is cold.

[tkent02]

I'm thinking maybe something like it's too lean and so it will only idle higher when there is extra fuel in there from the long deceleration? So maybe it is too lean. Or not. Maybe try moving the mixture screws half a turn to see what it does, if no good try the other way?

[RHODESIA SMITH]

Thanks Chaps


quite right I forgot to mention the bike is a GS850Gx - 1981.

will give that a go, turning the idle mixture screws equally out about an 1/8th.

carb sync is good, intake 0-rings are new- I have done as per this forum and Bass Cliff info, plug chops ect-- everything looks grand.

Possible that the reasonably long decceleration scenerio could be correct.

Lean- I am not entirely convinced as all else shows me otherwise that it is not. However I will not disregard totally, and will look a further into that.

can be possibly an ignition timing issue? The advance mechanism on the bike appears clean and in good condition, it does move freely and the springs tensions are reasonable taught. Screws for the base plate ect are tight.

I do know these bikes having had 3 in my life so far , 2 850's and 1000. The first 850 had about million kilometers on it having bought it from a police auction when the old state disolved the well working police force in '94. Left it white and had endless hassels at road blocks so painted it green and filed off all the frame and engine numbers........ ha ha that is another story.