Throttle Maintenance

There’s nothing quite like the feel of a brand-new, smooth-running bike fresh from the showroom floor. Every component in its unused state simply fits tighter, runs smoother and feels better. If you ride your bike on a regular basis, than you know exactly what we’re talking about. Slowly but surely parts start to wear and collect dirt and grit, inhibiting their ability to function efficiently. And the throttle assembly on your four-stroke is no different than any other mechanical part on your bike. As the cables get dry and collect dust and dirt particles over time, they will start feeling rough, and may even bind, requiring more effort to twist the throttle. Not only could this cause performance issues with your bike, but it could ultimately cause performance issues with you as well. So pay close attention to our pal Aaron as he walks you through throttle cable maintenance and eliminate some of the premature aging of your steed…

REQUIRED TOOLS: 10mm T-handle, 8mm T-handle, Phillips-head screwdriver, contact cleaner, 4mm Allen wrench, 10mm box-end wrench, cable lubing tool, cable lube, Pro Circuit Red Lube (or equivalent)

Note: The following procedure was performed on Stephane Roncada’s Monster Energy/Pro Circuit/Kawasaki KX250F. Some steps may be slightly different if you’re not working on a KX250F or RM-Z250, so refer to your owner’s manual if needed.

Start by removing the seat and fuel tank in order to gain the access needed to remove the throttle cables at the carburetor. Next, jump up to the handlebars, pull back the throttle dust cover, and loosen the two bolts that are holding the two halves of the throttle housing together (two Phillips bolts on a KXF/RM-Z). With the end of the throttle tube now exposed, pull the cable ends (balls) out of the throttle tube. The tube and grip are now free to slide off the end of the bar. Now that everything is apart and exposed, clean the inside of the two throttle housing pieces, the throttle tube, and the ends of the throttle cables with some contact cleaner. Also, clean the handlebar of any dirt and grime that may be present.

On the right side of the carburetor you’ll find a single 4mm Allen bolt that secures a plastic dust cover. Remove the bolt and pop the cover off. With the cover removed, the ends of the two cables can now be accessed. Starting with the top cable, use a 10mm wrench to loosen the lock nut, and the cable end can be pulled off of the carburetor wheel. Repeat this process for the bottom cable. Next, while paying attention to the cable routing, bend back the flexible cable guides that are located on the frame near the headset, and pull the cables up and out of the bike.

It’s time to lube the cables. Because of the hardened metal elbows located near where the cables go into the throttle housing, I recommend lubing the carburetor end of the cables where a cable-lubing tool can be easily fastened. Note: It’s important to only use a minimal amount of cable lube. Because these are throttle cables, excess lube will eventually run its way down and into the carburetor. It won’t necessarily damage anything, but it will make a mess. Be sure to lube both cables. Holding the cables together, feed them back into the bike from the same spot you pulled them out near the handlebars. Rout them back in so they are tucked up tight against the right side of the frame to keep them out of the way of the fuel tank once it’s installed.

Before putting the throttle assembly back together, we recommend using Pro Circuit Red Lube or an equivalent on all of the moving throttle parts (the inside of the housing pieces and their edges, the balls of the cables and their slots in the throttle tube, etc.). Also, on the inside of the throttle tube put a small amount of cable lube so that it doesn’t go on dry against the bar. Because you can put the cables on backwards at the carburetor, start your reassembbly at the handlebar. With the throttle tube on the bar so that the cable ball slots are facing down, slide the cable ends back into the tube, and rout the cables back through the tube tracks. The cables can only go back onto the throttle tube one way. Once in place, line up the two halves of the throttle housings, and get the two Phillips bolts started without tightening them completely. To prevent binding and rubbing, push the tube and housing assembly together until it bottoms out against the end of the bar. Now, back the assembly off the end of the bar 1 to 2mm so that there is proper clearance to twist freely. Now tighten the housing bolts securely.

Before heading back down to the carburetor, push the throttle tube all the way forward until it stops. This will not only show you which cable to install first at the carb, but will also give you the proper slack needed to do it. At the carburetor, one cable will now be sticking out of the cable housing farther than the other. The longer one (the one with the most slack) is the one you’ll start with. It is the bottom or “pull cable. There is a 10mm nut that is thinner (not the locking nut), which slides into the groove on the carb. With the ball of the cable reinstalled on the throttle wheel, and the flat 10mm nut in its housing, tighten the 10mm locking nut to secure the cable. Next, turn the throttle tube back a little bit to take out the excess slack, which in turn will give you the slack needed to install the top or “push cable, and repeat the same process. I like to keep the gap between the 10mm locking nut and the longer 10mm adjusting nuts that are connected to the cable even between the two cables. Because most of the cable adjustment is done at the bar, you don’t need a lot of gap (2-3mm) between the locking nut and the adjusting nut of each cable. Once adjusted evenly, reinstall the dust cover and tighten the 4mm Allen bolt.

If you don’t have a personal preference for the amount of throttle play (movement front to back), I recommend about 2-3mm of wiggle, at most. To adjust the play, there’s a finger locking nut and an adjusting nut just behind where the cables enter the throttle housing. If you want more slack (play) in your throttle, spin the adjusting nut in toward the throttle. For less slack, back it out. Because it’s a push/pull style system, you have to adjust both cables evenly until you get the feel you’re looking for. After you’ve achieved your ideal amount of play, reinstall the fuel tank and the seat. Now that everything is back together, turn your bars from side to side to make sure that the cables aren’t binding anywhere, and then recheck the throttle play and adjust again if needed.