How to Adjust a Honda Elite SR50 Carburetorby Chris Gilliland
The Elite SR50 is one of the more notable, and commonly seen models within Honda's lineup of scooters and was produced between 1988 and 2001. The SR50's 49 cc two-stroke, single-cylinder engine was fed through a single carburetor hidden behind the air cleaner box on the left side of rear wheel. The carburetor used an adjustable air mixture screw that could compensate for slight changes in elevation or climate. Major elevation changes, typically more than 6,500 feet above sea level, could be compensated for through the replacement of the carburetor's main fuel jet. However, the engine's baseline idle speed must be set before beginning either type of adjustment.
Idle Speed Adjustment
Lift the scooter onto its center stand. Unlock the scooter's seat and raise it into a fully opened position. Unlock and remove the maintenance lid from the under-seat storage compartment, using the ignition key.
Start the engine and let it idle for three minutes to allow it to warm to its operating temperature. Do not stop the engine.
Clamp an inductive tachometer onto the spark plug cable, located at the center of the maintenance lid. Turn on the tachometer. Ideally, the engine should be idling between 1,750 to 1,850 rpm.
Locate the throttle stop screw through the access hole at the front of the air cleaner box on the left side of the rear wheel. The throttle stop screw is at the upper portion of the access hole. Turn the screw clockwise, using a flat-head screwdriver, to increase the engine idle speed. Alternatively, turn the screw counterclockwise to reduce the idle speed.
Twist the throttle grip quickly two to three times and let the engine settle back into a steady idle. Readjust the idle speed if it does not return to a range of 1,750 to 1,850 rpm.
Stop the engine. Remove the tachometer clamp from the spark plug cable. Reinstall the maintenance lid and lower the seat until it locks into place.
Compensating for Slight Changes in Altitude or Temperature.
Find the air mixture screw in the lower portion of the air cleaner box access hole, located at the front of the air cleaner box. Turn the air mixture screw clockwise with a flat-head screwdriver until it seats lightly against the carburetor body. Count the number of turns as you go. Ideally, the screw should be set to 1-3/8 turns from a fully-seated position if you are working on a 1988 through 1993 SR50 model, or 1-7/8 turns for a 1993 to 2001 SR50 model. Turn the screw back to its original setting or to the factory-specified setting corresponding to the model year of your scooter.
Lift the scooter onto its center stand and start the engine. Let the engine warm up for three minutes, but do not stop the engine.
Turn the air mixture screw counterclockwise a half-turn at a time and listen to the engine as it idles. Stop turning the air mixture screw as soon as the engine idle speed increases slightly, then turn the screw clockwise a quarter-turn.
Lower the scooter from its center stand and take it for a short test ride. The scooter should accelerate smoothly from a complete standstill. Stop and turn the air mixture screw a quarter-turn in either direction if you feel any hesitation when accelerating.
Main Jet Replacement for Elevations Above 6,500 Feet
Lift the scooter onto its center stand and allow the engine to cool for a minimum of 30 minutes.
Remove the center cover panel mounting screw, located between the seat hinge, using an Allen wrench. Pull the tab at the bottom of the cover out of the groove cut into the floorboard. Lift the cover up to free the tabs along the sides of the cover from the grooves cut into the side cover panels.
Remove the pair of bolts attaching the left side cover to the side of the floorboard, using an Allen wrench. Depress the center of the plastic push rivet attaching the rear of the left side cover to the scooter's frame, using the tip of a Phillips screwdriver. Pull the rivet out of the side cover, then slide the cover toward the front of the scooter to disengage the mounting hooks along the upper edge of the cover.
Unscrew all four acorn nuts attaching the luggage rack to the rear of the scooter, using a socket and a ratchet. Lift the rack away. Remove the screws attaching the rear of the upper left rear cover to the scooter, using a Phillips screwdriver. Remove the bolt from the front of the cover, using a ratchet. Pull the cover away from the scooter.
Remove the pair of hex-head bolts along the bottom edge of the air cleaner box, using a socket and a ratchet. Loosen the clamp attaching the air cleaner duct to the carburetor inlet, using a flat-head screwdriver. Pull the air cleaner box away from the scooter.
Unplug the automatic bystarter connector -- the large white connector along the positive-side of the battery.
Loosen the clamp attaching the fuel hose to the left side of the carburetor, using pliers. Pull the hose off the carburetor fuel inlet.
Unscrew the round top cap from the top of the carburetor by hand. Pull the throttle valve out of the carburetor. Do not remove the cable from the top cap and throttle valve.
Unbolt the carburetor from the engine, using a socket and a ratchet. Hold the carburetor over a drain pan, then loosen the float chamber drain screw at the bottom of the carburetor, using a flat-head screwdriver.
Flip the carburetor over so the float chamber faces upward. Remove the float chamber from the carburetor, using a Phillips screwdriver. Unscrew the main jet from the taller tower at the center of the carburetor, using a flat-head screwdriver. The original main jet is intended for use below 5,000 feet above sea level and will be a No. 88 for a 1988 to 1992 SR50, or a No. 78 for a 1993 to 2001 SR50 model. Keep this jet for later use.
Screw a new No. 85 main jet into the center tower if you are working on a 1988 to 1992 SR50, or a No. 75 for a 1993 to 2001 SR50. Tighten the jet until it is seated snugly in the tower. Reinstall the float chamber and snugly tighten the screws.
Reinstall the carburetor onto the engine and push the throttle valve into the carburetor. Screw the top cap snugly into place by hand. Push the fuel hose onto the fuel inlet and move the clamp into place over the end of the hose.
Push the air cleaner box duct over the carburetor inlet and mount the air cleaner onto the scooter's frame. Tighten the air cleaner box and air duct clamp until they are snug.
Reinstall the left rear cover, left side cover and center cover panel onto the scooter. Reinstall the luggage rack and tighten the acorn nuts to 10 foot-pounds, using a torque wrench.
Turn the air mixture screw counterclockwise a half-turn if you are working on a 1988 to 1992 SR50. Alternatively, turn the throttle stop screw clockwise a half-turn, if you are working on a 1993 to 2001 SR50
Warm the engine and reset the idle as outlined in Section One. Test ride the scooter and adjust the air mixture screw as needed, using the procedure outlined in Section 2.
- Work slowly when adjusting the air mixture screw. Big changes can occur with the slightest of adjustments, making it easy to overadjust the screw and completely miss the sweet spot that can make a difference in the performance of your scooter.
- Never smoke or work near an open flame when you are servicing your scooter's carburetor or fuel system. Fuel vapors can ignite in the presence of either and cause serious injuries, as well as damaging the scooter.
- Transfer the old gas that was drained out of the carburetor from the drain pan into a gas can. Take the old gasoline to an automotive fluid recycling center for disposal. Do not reuse the gas in your scooter to prevent the possibility of contamination.