Daves Mod

XR650L Carb Mods by Dave Closs and Brian Jackson, minor revisions by Jets R Us


These mods help correct the stock lean condition.Power increase and throttle response will be better. Though intended for 1993-2004 Honda XR650L models, these carburetor mods may work on other model bikes that use the Keihin 42.5mm diaphragm-type CV carb.

1) Make sure the fuel petcock valve is set to off. Drain carb of gas.

2) Disconnect the fuel line at the carb and remove the seat and fuel tank.

3) Remove the throttle cables, hoses, choke cable, fuel line, rear brake reservoir and its bracket. Make sure to note all connections so you can put things back to where they were.

4) Loosen the hose clamps on both sides of the carb.

5) Squeeze the intake tube (from the airbox to the carb) back and out of the way. You can pull the carb out of the frame now to the right side quite easily. Cover the intake to the head with at least a clean towel. Make sure not even dust gets in there.

6) Remove the top and bottom plates of the carb by removing 4 screws on each end. These screws can be replaced with M4x10 and M4x12 socket head screws, 4 of each stainless steel preferred.

7) Remove mixture screw now that it can be turned.

8) Grind off the tab on the mixture screw as shown, or as Dave did, grind the tab off the carb body instead of the mixture screw. See the following photo for the tab on the carb.

9) Reinstall by turning all the way to the bottom, lightly seating it and then backing it out appropriately. Start at roughly 2.5 turns out.

10) Remove large spring and slide from top of carb, under the top cover.

Needle Shimming. When removing the slide, the needle is held into the bottom of the slide by a little yellow widget that you press down on and turn a little with a screwdriver or an 8mm socket. When you remove the little yellow widget, the needle comes right out. Notice the needle sits in a small recess. Find a small washer that is 0.020-0.030" thick and fits fairly snugly over the needle at the thickest part at the top. Stainless steel washers are preferred. The needle will be raised by the thickness of the washer.

11) In the bottom of the slide, drill out the two existing holes to 5/32" per the photo.

12) Reinstall with washer removed earlier and align the tab correctly.

13) On the bottom of the carb, remove the plastic piece (baffle) that is partially covering the pilot/slow jet. Note: If you use the longer style pilot/slow jet, you will need to clearance the baffle to accommodate it.

14) Gently unscrew the brass jets. The longer larger one is the main jet and the shorter flush-mount one on the pilot or slow jet. Gently screw in the new jets.

15) Place the plastic baffle back over the main jet and install the carburetor bowl.

16) That is the end of the carb mods. Check for smooth operation of everything and reinstall the carb on the bike. After installation, recheck the operation of the throttle and adjust of necessary.

Jetting Suggestions
With the stock exhaust at sea level and no gasohol, the jetting should be around 55/158. Jet leaner for higher altitude, richer for gasohol, or richer for aftermarket exhaust, see rejetting 101.

Important Note
These XR650L carburetor modifications work in conjunction with a free-flowing aftermarket style air filter and removed airbox snorkel. If performance items are added then the carb will need to be rejetted, see rejetting 101.


Credits: This article was published from forum topics posted by Dave Closs and Brian Jackson. Edited by 4Strokes.com and jetsrus.com