02' 426 idling high...

Not sure whats up. The bike will idle high for awhile, then suddenly drop to normal. Then when I gas it again, it takes awhile to idle down again. Cables and throttle plate are lubed. It seems to run fine, barring this odd behavior. Air leak??

I'm fairly carb illiterate. What does an externally adjustable fuel screw do, and what are the steps to tuning one? I did do the acc pump screw stop mod and that helped a ton!

Thanks all,


You are too lean on the pilot go one up and try again

... or the pilot jet is slightly clogged or.... the fuel screw needs a slight adjustment. If this idle problem is new, try cleaning or better still, replacing the pilot jet. While you are doing this, if you have not already done so, replace the stock fuel screw with an extended one, like the screw by Merge Racing. If the idle issue still exists, you may have a slight vacuum leak. If the problem has always been there and tweaking the fuel screw does not resolve it, then a larger pilot may be called for.

Fuel Screw/Pilot Jet

Fuel screw settings in the 'book' are recommended starting points. Every bike is different, as is the temp and altitude. Set the screw according to this method.

Gently turn the screw all the way in. Now back it out two turns. Start the bike and fully warm it up, go for a 10 minute ride. Set the idle to speed to 1,500~1,800 RPM as best you can (I know, without a tach this is tough, just set it to were it idles relatively smoothly). Once warmed, slow the idle to the lowest possible speed.

*** When turning the fuel screw, keep an accurate 'count' of the amount you are turning it and record it in case you have to reset it for some reason. Makes life easier when you can just set it from notes Vs. going through the procedure again.***

Turn the screw in until the idle becomes rough or the bike stalls.

if it stalled, open the screw about 1/4 more turn. Restart it and slowly screw it in till you can just perceive a change.

If the screw can be turned all the way in and the bike still idles perfectly and does not stall, then you need to go down a size in pilot jet.

Now very slowly, open the fuel screw till the idle is smooth. Blip the throttle, let the bike return to an idle, wait say ten seconds. Confirm it is the same smooth idle.

If the screw has to be opened more than 3 turns to get a smooth idle, you need to go up a size in pilot jet.

If you find it does not stall with the larger jet but has to be open more than three turns with the smaller pilot jet, put the larger one in and set the fuel screw at 1/2 turn.

If the idle speed increased, adjust the idle speed knob to return the bike to a real slow idle speed. You must then re-visit the fuel screw. Keep doing this till the fuel screw is opened just enough to provide a nice steady idle at the lowest possible RPM. Once this is done, increase the idle speed to the normal one for your bike, typically about 1,800 rpm, but go by the spec in your manual.

i had this problem on my old 426, and i found that there was an air leak from the rubber boot between the carb and the head. and when i replaced it and setup the carb like what is described above, it was all good to go.

Thanks guys! Sorry for the late reply. I can NOT figure out how to get email notification. Everything seems set correctly but I just dont get the reply emails...

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now