Step by step: From general maintenance to complete restorations, we share tips and tricks for working on classic bikes.
If you’ve replaced carburetor throttle cables on a vintage 4-stroke engine, you know that the basic process is relatively simple. The complicating factor for anything other than a single-cylinder engine is making sure the carburetor slides are synchronized to each other so they pull off idle evenly. If your carbs are adjusted properly before you replace the cables, getting the slides synchronized isn’t that difficult, as we describe.
Vintage Yamaha 2-strokes equipped with Yamaha Autolube oil injection have one more component. These bikes have a cable working in conjunction with the throttle cables, operating an oil injection pump and increasing oil pump flow as throttle is applied. As a result, a 2-cylinder Yamaha 2-stroke such as our subject 1973 RD350 has four cables — two carburetor slide cables, one Autolube oil pump cable and one throttle cable at the handlebar twist grip. Additionally, the multicable setup has a cable junction that links the top or twist grip cable to the carburetor and oil pump cables. The cable junction can fail, falling apart from years of use. On our bike, a previous owner had clamped and zip-tied the junction to keep it in one piece.
If any one of these cables breaks or is damaged, you’re likely looking at replacing the entire cable assembly, as individual cables are increasingly difficult to find. Yet replacing them as a set is a good idea, as cables are service parts that have to be replaced occasionally. Regular use takes a toll, leading to stretched cables and worn-out cable housing ends. Nonuse does, too, resulting in sticking cables from years of sitting.
Original “repaired” cable junction was on its way out.
Fortunately, thanks to specialty parts providers like HVCcycle, complete cable assemblies for Yamaha 2-stroke twins are readily available.
Replacing the cables isn’t a particularly difficult job, and can be done by the average home mechanic in a few hours. You won’t need any special tools, but like so many of these projects, patience is the single most important ingredient to success.
Protocol is important in this project, as well: With the new cable assembly installed, it’s important to first synchronize the carburetor slide pull, followed by the oil pump pull, and finally by removing any excess cable play using the adjuster at the handgrip.
Doing this job revealed a few other tips. Tip 1: If your RD still has the original rubber carburetor air intake boot, replace it at the same time. It has to come off and it’s probably hard as a rock; getting old ones back on is a bear. Tip 2: As you install the new cable, make sure the cable ends fit into place properly. On our oil pump cable, a slight excess of solder on the cable end barrel kept it from properly slotting into place on the oil pump pulley. The fix was easy: Using a small hand file, we gently filed off the excess solder until the cable dropped smoothly into place. It didn’t take more than a few minutes to address.
A complete assembly from HVCcycle was $70.95, and the one we received was as good if not better in quality than the original. As always, having a good shop manual at hand will help you work through the process. Happy riding!
1. Disconnect the fuel line at the petcock and drain the gas tank into a container.
2. With the gas tank drained, disconnect the fuel crossover line and plug the line and the tank outlet. The crossover runs from the left to right side of the tank; you only need to disconnect one side to remove the tank.
3. With the gas tank off, unscrew each carburetor slide cover and remove the slide assembly. The accelerator cable slots into the bottom of the slide, held in tension by the slide spring. Compress the spring and release the cable.
4. With the cables removed from the slides, remove two screws securing the right control assembly and cable stay plate. Pull the top half away and unhook the cable from the twist grip.
5. With the accelerator cable disconnected from the twist grip, thread the upper cable down between the handlebar and instruments and pull it free. Note the cable routing guide on the left side of the steering head.
6. Next, remove the right side engine cover to expose the oil pump. Rotate the oil pump pulley counterclockwise and release the cable from the pulley. Unscrew the cable housing from the side cover and pull the cable free.
7. Next, thread the upper section of the new cable through the cable guide at the steering head and up between the handlebar and instruments.
8. Lightly grease the handlebar end and the cable barrel. The original cable has a rubber sleeve to hold the cable housing tight in the assembly. Reuse it if possible. Pull the cable through the lower half of the control assembly and secure it in the twist grip. Secure the two halves of the control assembly and the cable stay plate.
9. Next, route the oil pump cable through the side cover and screw the cable housing into the side cover.
10. With the cable housing screwed into place, rotate the oil pump pulley counterclockwise and secure the cable end barrel into the pulley.
11. Attach the accelerator cables to the carburetor slides. The easiest way is to first slot the cable into the slide, followed by the slide needle and retaining plate. The spring can then be wound around the cable, compressing it as it winds on, until it’s fully in place.
12. Install the slides in the carburetors, followed by the carburetor slide covers. Remove the right side panel, loosen the clamp securing the intake boot to the air filter housing and the clamps securing the boot to the carburetors and remove the boot.
13. Next, lift the seat and loosen the clamp securing the oil filler tube to the oil tank. Remove the two bolts securing the oil tank. Pull the oil tank far enough away from the frame to disconnect the oil breather hose. Next, remove and cap the oil supply outlet and tube and remove the tank.
14. To adjust the carburetors, first make sure both cables are slack and that the slides are resting on their idle stop screws. Using your fingers to feel the slides for movement, adjust the cable tension at each carburetor to take out most of the cable slack.
15. Using your forefinger and thumb, feel the carburetor slides for even lift as you pull the twist grip; they should rise simultaneously. If not, slowly adjust the cable tension on the “slower” slide until it lifts evenly with the other slide.
16. With the slides set, lock the cable adjuster at the carburetors by setting the lock nut on the housing.
17. Next, set the oil pump pull. Turn the throttle twist grip until the carburetor slides are just starting to lift, then adjust the oil pump cable housing until the index mark on the oil pump pulley lines up with the pin on the oil pump plunger.
18. To finish, reinstall the engine side cover, the air intake boot, the oil tank and right side panel, and the gas tank. Finally, remove any cable slack at the twist grip by adjusting the threaded cable barrel at the twist grip.