Sign in to follow this  
Followers 0
pd10913

XR600 Fuel Screw Adjustment

5 posts in this topic

98' XR6- have just fitted an FMF Powercore 4, ground header welds, airbox snorkel removed, everything else stock. I'm thinking 155/68 jet setup but can someone tell me the best way to adjust the fuel screw and if the suggested jets should be ok with this setup, thanks

Share this post


Link to post
Share on other sites

Its actually an air screw and needs to be 2 5/8 turns out from fully seated. You are pretty much spot on with the jetting.

Share this post


Link to post
Share on other sites

It is a fuel screw, not an air screw. Nearly all four stroke carbs have fuel screws while nearly all two stroke carbs have air screws. If in doubt you can tell which one you're dealing with by it's location on the carb. If it is on the engine side of the carb it is a fuel screw. If it is on the air filter side of the carb it's an air screw. Said another way, if it's in front of the slide it's a fuel screw. If it's behind the slide it's an air screw. The distinction is important because they work opposite one another. In is lean for a fuel screw while in is rich for an air screw.

The short(ish) answer on finding the best setting is:

--Warm up the bike to full operationg temp.

--Turn up the idle slightly (a few hundred RPM). This is only to help distinguish small changes in idlel speed during the following steps.

--Turn the screw in until the idle starts to drop and/or miss a little. Note that position.

--Now turn the screw out until the idle starts to drop and/or miss a little. Note that position.

--The ideal setting is half way between the two noted postions.

--The goal is to find the setting that provides the smoothest and highest idle speed.

--Readjust the idle back down to the correct speed after the screw has been set.

--Typical settings are between 1 1/2 and 3 turns. If the best setting is more than 3 turns out the pilot jet is too small. If the best setting is less than 1 turn out the pilot jet is too large.

Share this post


Link to post
Share on other sites

HawkGT's advice is on the money. I have had two stock XR600s, a '91 and a '95 and a '98 HRC 628. Best jetting for all three was 160 - 162 main, 68 pilot. Altitude here ranges from 500 - 900 ft.

Share this post


Link to post
Share on other sites

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
Sign in to follow this  
Followers 0