Yes,another idle problem

[Elwarno]

I would pull my hair out if i didn't shave my head.I have been round and round with this bike since i bought it.I could tear the carbs down and reassemble them blindfolded.Ok.........I have a yoshi pipe,jetted carbs(stage one),and a k&n fliter (yes,I have the correct velocity ring on for jetted carbs).This thing runs and idles like a friggin top when it's first fired up.Go for a ride and come to a stop and she drops to where the idle is set,hangs for a second,then bogs and finally dies.Everyone on here is tellin me to ditch the k&n filter and put the stock in.Ordered one,it's on the way.In the meantime I took off the filter and still no luck.Does the same thing.So I adjusted the choke cable to crack the choke so I could get an idle out of it.What does this mean?My compression on all cylinders excedes suzuki's min. requirements.all cylinders fire.mixtures are correct.It really runs great when riding.It just will NOT idle.God please help me.It's just blowing my mind that I have not figured this out.

[The CyberPoet]

OK, here's what's happening (so you understand it):

The engine generates vacuum as the piston falls.
This vacuum moves backwards through the carbs, where it sucks air through them, causing the fuel to mix in.
The amount of vacuum at the carb dictates how much fuel gets mixed in. How hot the engine is dictates how well the fuel vaporizes.
The more resistance the air filter creates, the the higher the vacuum level at the carb, and the easier time it has sucking up fuel. The OEM has a fairly high resistance; the K&N has a medium-to-low resistance (depends on how well oiled it is); no filter at all effectively has virtually zero resistance.
When the engine is cold, the parts are looser, so it doesn't build as much vacuum as it will when it's hot and the valves/rings expand.

So (IMHO) it sounds as if the pilot screws/idle settings are set too rich. When the bike is cold and the vacuum is minimal, it pulls just the right amount of fuel to idle (good idle with a cold engine). When it gets hot, the vacuum increases (clearances tighter) and the fuel vaporizes better, so the mixture becomes too rich -- so rich that it doesn't want to idle on it.
Solution: reduce the fueling in the idle circuit and expect to need to use the choke to get it started.

Definitive answer: Get it on a dyno with an exhaust analyzer and get the dyno-tech to print out the fuel-air ratio analysis from the exhaust readings. Once cold, once hot. Then you'll definitely see what is occurring.

Cheers,
=-= The CyberPoet

[Elwarno]

Awesome.Thanks for the education cyberpoet.That helped me out a lot.Now,let me ask you this.Or anyone else for that matter.I've replaced about every piece you would want to replace on my carbs except for the o-ring on the mixture screws.Is it common for these harden and let air slip past the mixture screw?Dynojet recommends I turn my mix screws about 2 1/2 turns out for my jet kit.Now I have it running with 2 of the carbs about 1 turn out and the other 2 about a half a turn out.This don't seem like much.So am I turning them out so little to compensate for these bad o-rings?Am I on to something here possibly?

[Black_peter]

Change the o-rings before going too crazy adjusting things. Those o-rings can get squashed, dry, torn etc..

[The CyberPoet]

I'm with BP -- replace them.
If you can get the bike to idle at 1 turn out or 1/2 turn out, then those O-rings are decimated or missing... or something else is very very seriously amiss (like the needle not seating).

Cheers,
=-= The CyberPoet

[md86]

Um , yeah ....... My "problem cylinder" seems to like it best when I back the pilot screw to less than stock , so it's at about 1 turn out now . I think I ordered a pilot o-ring (was on my list) , but we'll see how long it takes for Ronayers to get off their ass .....