Runs great but dies immediately at idle.

[Vloukole]

Hi guys

My 1981 GS1000g runs very well to redline but wont idle at all.
Carbs are cleaned (dipped), Valve clearance adjusted, no leaks on the intake side.

Bike starts easy but have to apply throttle to keep it from dying. When it revs and I let go of the throttle, it drops straight down and dies. It does not even idle for a sec.

Is that a rich or a lean idle?

(I did search the forum for answers but nobody has the EXACT same problem)

 

[Vloukole]

Oh yes and stock jets and needle at the third position.

 

[tom203]

Of course you have played with idle stop screw when bike is warmed up.........?? To no avail?
When you let go of throttle, bike needs enough mixture thru its pilot system to support life! How far out are your mixture screws?

 

[Vloukole]

Yes I did. When I turn it up the revs will hang a bit. I set the pilot screws from 2 turns out to 4 turns out. I used a colourtune but the colour did not change from a light blue colour.

 

[hannibal]

What so you mean the revs hang a bit? Will it idle at high rpm or does the idle still fall and die?

Sounds like a bad idle circuit. Will it keep running at 1/2 throttle? 1/4 throttle?

Maybe you have broken pilot screw. 4 turns seems like a lot to not make a difference.

 

[Vloukole]

Yes it will idle at about 2000rpm if I set it there but will hang then. It runs good when I use the throttle. Only dies when it has to idle.(closed throttle)

 

[hannibal]

I thinking it's a blocked idle circuit in the carbs. Did you spray carb cleaner in every passage you could find? Then follow with compressed air? The idle passages supply fuel at idle, then another jumps in at 1/4 throttle (can't remember but i think it's the pilot circuit). So if it runs well at everything but idle and will run if you turn the idle way up, I'm guessing the idle passages are clogged.

 

[60ratrod]

Have you bench sync or vacuum sync'd the carbs. I had a similar issue with my 650g until i vacuum sync'd it

 

[Vloukole]

It must be clogged. Will clean them with carb cleaner and compressed air tomorrow. Will just removing the pilot screw and pilot jet be enough to spray the carb cleaner in or do I need to take it apart?

 

[tom203]

It must be clogged. Will clean them with carb cleaner and compressed air tomorrow. Will just removing the pilot screw and pilot jet be enough to spray the carb cleaner in or do I need to take it apart?

You might get lucky with this approach, but the passage from pilot jet up to mixture screw is tiny, check your mixture screws to make sure tips ain't damaged and giving you erratic settings.

 

[tom203]

The forum is fighting me!

 

[Vloukole]

60ratrod, I bench sync'd the carbs. I dont have a vacuum sync. I tried to be exact with the bench sync. Measuring the gaps to a T. Pilot screws looks good still.

 

[Vloukole]

I cleaned the pilot circuit and tried to set the idle. It ended up being perfect at 5 turns out. Can I leave it there or do I have to go up 1 size on the pilot jets?

 

[tom203]

I cleaned the pilot circuit and tried to set the idle. It ended up being perfect at 5 turns out. ....

Me confused ! What's 5 turns out? The idle stop screw or the individual mixture screws? The former doesn't mean much.

 

[60ratrod]

I'm sure he's talking about the idle screws. That seems to be really far. Normally you shouldn't be past 3-3.5 turns out on the idle screws. Does it have pods?

 

[Vloukole]

Yes it is the idle mixture screw. No pods.

 

[tkent02]

Humor me here, perhaps I missed something but what did you dip the carburetors in and for how long? What was the rest of your cleaning process?

 

[Vloukole]

Dipped it in acetone for a night and used compressed air on all the passages. There is no real carb dip available here.

 

[Vloukole]

All the plugs are tan coloured.

 

[tkent02]

Dipped it in acetone for a night and used compressed air on all the passages. There is no real carb dip available here.

Do you have ultrasonic cleaners? They work better than any dip anyway.