Carb air screws

[crazyfish]

Hey guys,

I'm currently rejetting my bike after installing new air filters and taking out a 33bhp restrictor kit, and while trying to set the idle mixture I noticed that only the airscrew on one of the carbs makes any difference. The one on the left hand card can be fully in, fully out, whatever and it makes no difference at all. Im guessing this isn't normal. Any ideas on what might be wrong? Clogged pilot jet on that side or something?

Setup:
2000 GS500E, 40 pilots, 145 mains (although this is just a first guess, not got round to checking more than idle mix yet, suggestions welcome)
Uni pod air filters (K&N knock offs)
Otherwise stock.

[joshr08]

is your bike running on both cylinders?

[johnny ro]

what does the restrictor kit consist of?

This sounds like a job or Buddha.

[crazyfish]

The restrictor kit was just a couple of large washers between the carbs and the cylinders to restrict how much air can get through. I've taken them out now but that means new main jets. (the pilots were already 40s). I think the main jets that were in there while restricted were 137.5s and it ran like a charm.

It doesn't sound like its running on only one cylinder, what's the best sure fire way of checking?

Thanks

[joshr08]

pull a plug wire and see if the bike changes how it is running when you pull it then put it back on and check the other one.

[rger8]

Crazyfish,

Funny you brought this up, I was gonna post the same question. I was putting my new/used 2006 back together yesterday after cleaning out the clogged pilot jets and decided to drill the brass caps out and richen the stock settings. One carb was set at 1 3/4 turns out so I set to 2 3/4. On the other carb the fuel air screw was seated all the way in. My brother checked it as well and agreed, so I backed this one out 2 3/4 turns as well.

So here is the deal. When I bought the bike last week and test road it of course it ran like crap below below like 20 mph and for sure wouldn't idle without the choke on but once I got her passed that I got her to 80mph and ran smooth as silk. How can this be when one carb screw was fully seated? I was thinking the same as you! Don't both carbs have to be set about the same? If one was fully seated wouldn't it be running really lean or is this they way they come from the factory? I'm perplexed  

Hope someone gets back to you on this, it's kinda strange

PS - My bike is bone stock and seems to run great now. Maybe we only need one carb on our bikes

[crazyfish]

Once you get to 80mph yo wont be running it at idle so you'll be using the main jets and not the pilot jets so the air screws make no difference. If you've got a rough idle it will be because one of your cylinders only starts firing once you get off the pilot jet.

The pilot screws only affect the mixture with no throttle really.

Ill have a poke around and see if the pilot jet is blocked or somthing on that side.

Seems a bit odd to me...

[rger8]

Crazyfish,

When you say "air screw" are you saying the fuel/air mixture screw? I thought these where important for setting a lean or rich mixture. These are the ones I thoght you were having problems with. Maybe I don't get it Like I said, after I cleaned my pilot jets out it seems to idle fine now. I was just wondering with one of the air/fuel screws turned all the way in and the other one turned  out1 1/2 turns out I wouldn't think it would run so good at the higher RPM's. I thought they were both supposed to be turned out the same!

Maybe I'm lost on this

[black and silver twin]

the idle mixture screws only change the idle and just-off-idle mix. they have almost no effect above 3000rpm. also try setting both mix screws the same, around 2-2.5 turns out at first.

[crazyfish]

Update:

I ripped apart the carb on the side that wasn't working and made sure all the jets were clear and suchlike, put it all back together and cranked the engine. Works a bit better now, the screw on the left carb now makes a bit of a difference but almost nothing at all compared to the other one. Its working fine enough for me so im not going to worry about fiddling too much with it anymore. The idle mix seems alright.

Gotta get down to tuning the rest now though, and roads are too icy to ride much at the moment.....      ..... helpful.



yeah rger,
In the carbs there are two routes for the air to go, either through the pilot circuit or the main. The throttle controls how much goes through the main circuit. With no throttle, almost nothing goes though the main and so you rely entirely on the pilot ciruit (whose mixture is controlled by the screws), with more throttle the main ciruit takes most of the flow because its much bigger than the pilot circuit. The mixture in the main circuit is controlled my the main jet and the needle setting (Not the air screws). So adjusting the air screws only changes the mixture at idle. At higher rpm (or at least more throttle), you're using mostly the main circuit and so the settings on the pilot ciruit (Like the air screw) will make almost no difference.

Hope that helps.

[ohgood]

Update:

I ripped apart the carb on the side that wasn't working and made sure all the jets were clear and suchlike, put it all back together and cranked the engine. Works a bit better now, the screw on the left carb now makes a bit of a difference but almost nothing at all compared to the other one. Its working fine enough for me so im not going to worry about fiddling too much with it anymore. The idle mix seems alright.

Gotta get down to tuning the rest now though, and roads are too icy to ride much at the moment.....      ..... helpful.



yeah rger,
In the carbs there are two routes for the air to go, either through the pilot circuit or the main. The throttle controls how much goes through the main circuit. With no throttle, almost nothing goes though the main and so you rely entirely on the pilot ciruit (whose mixture is controlled by the screws), with more throttle the main ciruit takes most of the flow because its much bigger than the pilot circuit. The mixture in the main circuit is controlled my the main jet and the needle setting (Not the air screws). So adjusting the air screws only changes the mixture at idle. At higher rpm (or at least more throttle), you're using mostly the main circuit and so the settings on the pilot ciruit (Like the air screw) will make almost no difference.

Hope that helps.

could be:

low compression
bad sync
bad vaccuum leak
bad plug
bad wars
but definitly nothing to do with your tars. this time

[rger8]

Crazyfish,

Hey thanks, I learned something there! I just finsihed cleaning out my clogged pilots and she is running 100% better and seems to idle fine once warmed up. When setting choke for warm-up she seems to be a bit erratic with RPM kinda going up and down by it'self but that only seems to last about 2-3 minutes. I think she is good for awhile.

Thanks for the education!

[crazyfish]

cheers ohgood,

I can't really be bothered checking compression, I don't have the gear, but is the fix for that new cylinder rings? The bike isn't running badly enough for me to go through stripping down the engine completely at the moment...

How do I fix sync/vacuum/wars?