Note: Previous forum logins will not work on our new forums. Registration is required.

Dave's Carb Mods

Existing technical info specific to Honda.
Respond to topics with questions or comments.
Post new topics in Honda Community.
User avatar
Site Admin
Posts: 895
Joined: Mon May 02, 2016 8:06 pm

Dave's Carb Mods

Postby 4Strokes » Tue May 03, 2016 10:47 am

XR650L Carb Mods by Dave Closs and Brian Jackson
This XR650L carburetor modification to commonly referred to as Dave's Carb Mods or Dave's Carb Mod. Below is a republished article of Dave Closs and Brian Jackson's XR650L carb mods that was originally posted in our Forums. These mods may correct the stock lean condition thus allowing the motor to run much cooler. Also the low and mid range power will increase substantially and throttle response will be liquid smooth compared to stock. Brian considers this almost mandatory for any XR650L. 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) Be clean as possible. Clean the carb exterior really well before removing it so nothing gets into the intake manifold or head. Always clean out all metal shavings and dust from the carb before reassembly. Before starting any work run your carburetor dry of gas. Do this by running the engine with the fuel petcock valve off until it dies (runs out of fuel).

2) Make sure the fuel petcock valve is set to off. Disconnect the fuel line at the carb and remove the seat and fuel tank.

Cables and Hoses
Items to Remove
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 either end 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.

Remove Top and Bottom
6) Remove the top and bottom plates of the carb by removing 4 screws on each end.

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

Mixture Screw Mod
Cut Mixture Screw
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.

Cut Mixture Screw Installed
9) Reinstall by turning all the way to the bottom, lightly seating it and then backing it out appropriately. (Most seem to think 2-1/4 to 2-1/2 will run best.)

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

Needle and Washer
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. The needle will be raised by the thickness of the washer. If you don't already have a washer that works, check your local hardware store. Some folks have found a similar washer in a kit from Radio Shack.

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

12) Reinstall with washer, as removed earlier. Make sure to seat the slide bowl (terminology?) properly and align the tab correctly.

Clearanced Slosh Baffle 1 - Viewed 5507 times
Clearanced Slosh Baffle 2 - Viewed 5507 times
Clearanced Slosh Baffle 3 - Viewed 5507 times
13) On the bottom of the carb, remove the plastic piece (slosh 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 slosh baffle to accommodate it.

New Jets Installed
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.

Slosh Baffle Mod
15) Place the plastic piece (slosh 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, clean well with carb cleaner, 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.

Important Note
These XR650L carburetor modifications work in conjunction with a free-flowing aftermarket style air filter and removed airbox snorkel. These modifications might actually make your dirt bike run worse without replacing the stock air filter and pulling the air-box snorkel.

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

Disclaimer: This article is intended as a guide only. No responsibility is taken by Dave Closs, Brian Jackson or

Return to “Honda Technical Reference”

Who is online

Users browsing this forum: MSNbot-Media and 2 guests