Not returning to idle speed

[jurgenkoppen]

Hey carb masters,

The most recent phenomena in my carb world is a very hesitant return to idle speed when I let off the throttle.
When pulling the clutch the rpms hover for a few seconds around 3000rpm and then slowly drop off.
Interestingly if I turn down the idle screw it will make the issue less extreme, but then my idle ends up to be too low.
My guess is sticky sliders, but before I pull the carbs I wonder why do they not return easily. Is there a spooge hole somewhere in the carb body which is plugged and otherwise would allow air to be let in once the vacuum from the engine stopped pulling up on the diaphrams?
Anyways, any pointers in the right direction would be appreciated, so I do not have to spend half a dozen times of installing and uninstalling carbs.
You all know the routine,eh?
Cheers, Jürgen

[geniusloerts]

before digging into the carbs, do i a simple check of your throttle cable to be sure it is not binding or needs some lube. then go into the carbs from there..



could save some time and stress

[AlanB]

Hi J-K,

Does it return quick if you put a finger on the top of the linkage?..... If so, it is either a sticky cable, something interfering with the linkage, or a lack of free-play in the cable.

Start there; if it doesn't help, the next step is a vac. leak (start looking round the nipples on the boots) Then you will need to head into the carbs.

Wildly wrong pilot adjustments can give the symptoms you describe.

Best of luck!

AlanB

[TADracer]

This can happen if one of your carbs are out of sync with the others. Takes a few moments for the three that are close to pull the rogue one down. If it is not the cable than I would check carb sync before you go into the carbs looking for something else.

[jurgenkoppen]

Thank you for your tips.
It is not the throttle cable, the linkage snaps shut the way it should.
So I will check for vac leaks, re-synch and go over the pilot set screws.
After all my reading on the subject, I am still not entirely clear on the pilot screw adjustment procedure. I recall that on this bike they were way out: 3 turns or so, and the sticky rpm problem was really extreme then. I reset them to about 2 turns out and it did help a bit.
The carb and engine are from a 79F now living in a 1980SG.
How about this direct question:
By turning in the pilot screws, I make the opening smaller as the needle does further into the hole. What I do not get yet, does this hole control fuel, or does it control air supply? With other words, does the idle circuit get leaner when turning the pilot in, or richer?
And what is the right setting?
Cheers, J

[TopCatGr58]

Hey Jurgen,

The pilot screw controls fuel flow, so you are leaning it when turning it in!

Take a look at this fine tech tip by Ken Talbot regarding tuning the pilot circuit , it's just one of many tips in the Tips, Maintanence, Carbs section which can be found by scrolling down from the MAIN FORUM PAGE, not just the link in the left column.
T.C.

[jurgenkoppen]

Thank you Top Cat, that was exactly the info I needed.
I knew it was somewhere on the forum, but I could not find it via the side bar links.
I will be in the know now.
You guys are the best....
Cheers, Jurgen

[skids]

Also, leaking air into the manifold boots can do that. Lets say you got them synched with a leaking boot at idle...then as you rev it higher, the vacuum characteristic changes and the leanness across the carbs changes.

Originally posted by TADracer
This can happen if one of your carbs are out of sync with the others. Takes a few moments for the three that are close to pull the rogue one down. If it is not the cable than I would check carb sync before you go into the carbs looking for something else.