Idle mixture screws

HalfLiterBeater · 09-01-2004, 06:59 PM

Where are the idle mixture screws on my carbs? They're on an 04 EX500...Keihin CVK's, I think they're 32mm carbs. It was set at the shop but now if I let it idle it will load up on fuel and stumble if I try to take off without revving it for a few seconds first. Also while I'm at it, are there any adjustment screws for upper-rpm fuel, or is that controlled by some other means?

I'm new to carbs...dealt with nothing but fuel injection for the past three years. So I understand EFI very well, but carburetors are foreign territory to me. Thanks all.

Oh and if anyone has a good website or any links to diagrams or schematics for these, it would be extremely helpful! None of the shops around here carry a Clymer's for this bike.

enos · 09-01-2004, 07:49 PM

Your idle screws are on the bottom of the engine side of the carb. You use a flat head screwdriver to turn them. Midrange rpm/throttle is controlled by the needles. You can raise/lower them, or replace with ones from a kit. Stock ones need to be replaced if you have filters/pipe. Full throttle is governed by the main jet. Put in a larger or smaller one to adjust. There may be a large overlap between the effects of the needle and main jet, so be aware when messing with those two. Any mc shop will order a manual for you.

HalfLiterBeater · 09-01-2004, 08:38 PM

Ok thanks man. My only other question is, I'm assuming the idle mixture and idle set screws are separate right? My idle speed is good, but the mixture is very rich.

Oni · 09-01-2004, 11:05 PM

Each carb has a screw on the bottom. Unless you're carbs have been jetted you have to drill the cap off. Then take a screwdriver and do 1/4 turns on each one until you have it figured out. Pretty straight forward.

enos · 09-02-2004, 10:26 PM

Quote:

Originally Posted by HalfLiterBeater

Ok thanks man. My only other question is, I'm assuming the idle mixture and idle set screws are separate right? My idle speed is good, but the mixture is very rich.

Here are the screws visible on the outside of the carb:
-idle mixture screw. you know what this does. Each carb has one of these.
-main idle adjuster (idle set screw?). There is only one of these (it's between the carbs), and its effect is just like twisting the throttle a bit. It essentially sets a lower limit for your throttle. This is a thumb screw. I think the 500 has it between the carbs, reach in from the back.
-synch screw. You get at this from the top. It is on the shaft that gets rotated when you twist the throttle. It is between the carbs. You use it to make sure both carbs' butterflies are synchronized. I.E. to make sure both carbs give the same amount of air/fuel. Don't mess with this one without a manometer (guages or mercury sticks). The shop probably set this for you.

Since your mixture is rich, when you adjust the idle mixture screws to make it leaner, the idle will rise. Turn it until you find the highest. Then lower the idle back down with the main adjuster (idle set screw). Then try turning the mixture screws again to see if you can raise the idle again. If not, you've got the best idle possible. Since your screws are on the bottom of the carb, turning them in (clockwise) = leaner, counterclockwise = richer. I recommend putting the idle low and making the tach needle be right on one of the lines on the tach. This way changes in the idle can be noticed easier. Be patient, sometimes it takes a couple seconds for the engine to react to the new mixture, especially when you're close to the correct one and don't rotate the screws by much.

HalfLiterBeater · 09-07-2004, 07:49 AM

Thanks big-time guys. I was out there for 10 minutes the other day and got the bike to stop loading up. Idle speed didn't really change...but I turned both mixture screws in about 1/2 turn each, and now it's not loading up the cylinders anymore.

Good info.