4Strokes.com Honda Tech: XR650L Carburetor Modifications - By Dave Closs & Brian Jackson Below is a republished article of Dave Closs and Brian Jackson's Honda XR650L carburetor modifications that was posted in the 4Strokes.com forums. These carburetor modifications will correct the stock lean condition, thus allowing the motor to run much cooler. Also, the low and mid range power is increased substantially and the throttle response is liquid smooth compared to stock. Brian considers this almost mandatory for any XR650L. These modifications should work on 1993-2004 Honda XR650L model years, but may also work on other models and years that use the 42.5mm diaphragm-type CV Keihin carburetor. Important Note: These XR650L carburetor modifications work in conjunction with a free-flowing aftermarket style air filter and removed airbox snorkel. These mods might actually make your bike run worse without replacing the air filter and pulling the snorkel. Be clean as possible. Clean the carburetor 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 carburetor 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). Make sure the fuel petcock valve is set to off. Disconnect the fuel line at the carburetor and remove the seat and fuel tank. 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. Loosen the hose clamps on either end of the carburetor. Squeeze the intake tube (from the airbox to the carburetor) back and out of the way. You can pull the carburetor 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 the top and bottom plates of the carburetor by removing 4 screws on each end. (Figure 3) Remove mixture screw now that it can be turned. (Figure 4) Grind off the tab on the mixture screw as shown in figure 5 and 6, or as Dave did, grind the tab off the carb body instead of the mixture screw. See figure 7 for the tab on the carb. 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.) (Figure 7) Remove the large spring and slide from the top of the carb under the top cover. The Needle: 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 meets the following: 0.020-0.030" thick and fits fairly snugly over the needle at the thickest part at the top. Just put the washer on the needle and slide it up to the top, as shown in the photo to the right. The needle will be raised by the thickness of the washer. If you don't already have a washer that works in this application, check your local hardware store. Some folks have found a similar washer in a kit from Radio Shack. In the bottom of the slide, drill out the two existing holes to 5/32” per the photo. (Figure 9) Reinstall with washer, as removed earlier. Make sure to seat the slide bowl (terminology?) properly and align the tab correctly. (Figure 3) On the bottom of the carb, remove the plastic piece (slosh baffle) that is partially covering the pilot/slow jet. (Figure 10) Note: If you use the longer style pilot/slow jet, you will need to clearance the slosh baffle to accommodate it. 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. (Figure 11) Place the plastic piece back over the main jet and install the carburetor bowl. (Figure 10) That’s the end of the carburetor modifications. Check for smooth operation of everything, clean well with carburetor cleaner, and reinstall the carburetor 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. The nipple on right side of carb (same side as choke insert port) and nipple at very bottom are vent/drain ports and were left unplugged using existing vent tubing. The front (outlet or cylinder head side) of carb has 3 vacuum nipples. 2 on top pointing up and one near the bottom pointing down. I plugged the one near bottom pointing down and the right side (closest to choke insert port). I routed hose from the upper nipple closest to throttle linkage up and around using existing metal eyeletts to the vacuum diaphram on left side behind throttle linkage. Rubber plug included in kit is for the airbox bottom. After removing all smog "stuff" including vapor canister, carb beather canister and diaphram, I cut existing breather hose to fit. Airbox upper large nipple to vac canister top, and vac canister side and bottom to T fitting and then to case breather. http://www.4strokes.com/images/forums/pics/XRnTahoe/7Hose2AirboxTop.jpg http://www.4strokes.com/tech/honda/xrlsmog/ http://www.4strokes.com/tech/honda/xr650lcarbmods/ All this and more found here----> http://www.4strokes.com/tech/honda/ http://www.4strokes.com/tech/honda/ Add a JE 10.5:1 piston (stock bore), WB All-Around Camshaft, 41mm Flat slide Mikuni Carb, port the cylinder head and installed a Pro Meg E-Series Exhaust and you can get 50hp, 41 foot pounds torque, out of your XR650L!! Still running pump gas. Just as reliable as ever! Now you have a real XR650!