This is why No3 cylinder wasnt firing....

[XTlegend]

Well, this moring I took the carbs off my other GS and put them on the problem one. Much grazed fingers later and it runs like a swiss watch. I cannot believe that I have missed anything on the problem carb but there you go. Talk about frustration! All good fun though (or am I kidding myself). Now more determined than ever to find out whats wrong. Thanks for all your suggestions.

 

[Steve]

... but in my case 4 new ones would almost cost what I paid for the whole bike!!.

I just LOVE this reasoning. I was given a bike a few weeks ago, for FREE. Does this mean that I should not have to pay anything for parts? :-k

Visually they look in sync - but what has this got to do with running on idle?? All pipes should get hot on idle with the throttle closed right? No 3 is cold initally then gets warm due to conduction from the head I guess. However if I start the bike from cold with choke ON then No 3 pipe gets hot otherwise cold. This implies compression is OK no?

"Sync" has everything to do with how it runs at idle.

What you are synchronizing is the opening of the throttle blades. You are trying to align them just fractions of a degree, but their effect is most pronounced as they just barely open. Looking at those fractions of a degree; #1 might be open 2%, #2 might be open 3%, #3 might be open 0%, #4 might be open 2%. If you open up the throttle just a little more, those numbers would be 9, 10, 7, 9. It's getting harder to see the difference. At wide open throttle, those numbers would be 99,100, 97, 99. Can you see why it's much more noticeable at idle?

My opinion is that you still have something blocking the pilot circuit in your #3 carb. First thing to check is for a broken tip on the idle mixture adjustment screw. You should be able to see a hole all the way into the throat of the carb when you remove the screw. There are more small holes in the top of the carb throat, right where the closed butterfly sits. These are what feed some of the mixture for the bike to run at low throttle openings. Their positions are staggered so they add fuel at different times. The adjustment screw only adds to what these holes can provide. It's not as easy to see if these holes are open, but you might be able to poke through them with a bent pin. Also make sure the holes in the pilot fuel jet are open. Finally spray some carb cleaner through the passages, followed by compressed air. I think you will finally clear it up.

It's nice to see that another set of carbs cleared the problem. At least now you know that it's not an electrical issue or something else and can concentrate your efforts on the carbs.

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