Vespa scooters, like any mechanical vehicle equipped with an engine, will run into problems over time due to wear and tear and the need for regular checks and maintenance. Knowing what issues can occur and what to look for can save countless hours of guesswork and frustration, as well as expensive mechanic's bills. Specifically, being able to change a spark plug, fix a flat or troubleshoot a tricky carburettor can be very helpful.
Inspect the fuel line from the gas tank to the carburettor and make sure it is not kinked or bent. Disconnect the hose via the banjo clamp by unscrewing it with a flat head screwdriver. Reattach the hose, after testing the gas flow, with the banjo clamp. Allow enough fuel to come through the line to push out any air bubbles. Confirm that the reattached hose is secure by using a new banjo clamp on the carburettor.
Confirm that the spark plug in the engine is the right size and heat rating. Use a socket wrench and appropriate socket size to remove it carefully (avoid stripping the cylinder cap threads). Compare the spark plug with the acceptable plug ratings in the owner's manual for your Vespa. Replace the spark plug if it is visibly dirty or oily. Adjust your carburettor for more fuel flow if the spark plug is powdery white on the tip.
Listen to the engine to determine if the revolutions are too fast or slow at idle. Adjust the air/fuel mixture needle in the carburettor manually to either slow down or pick up the speed of revolutions to a normal idle speed (the engine should run on its own without dying out or racing in idle).
Inspect for air leaks in the engine by looking for oil seepage from gasket points where engine parts are joined together. Examine the seal at the cylinder head to the barrel and the barrel to the engine. Look for leaks underneath the engine as well where the engine case halves join. Dismantle and rebuild the engine if significant seepage appears. Look for air leaks around the carburettor by confirming the carburettor and its box are bolted on correctly. Grab the carburettor box and make sure it doesn't wiggle. Perform the same test on the carburettor inside. Rebuild the installation with new gaskets if there is movement.
Inspect the two connection points for the engine to the scooter body: the swing arm and rear suspension. Try to wiggle the engine case by the swing arm. If there is significant movement, remove the engine and replace the motor mounts. Alternatively, test the engine mounts by driving the scooter into hard turns at speed. Confirm if wobbling occurs from the rear wheel while driving. Remove the engine and replace the defective motor mounts.
Confirm that the gear lever cables are connected to the gear handle securely. Identify any slop or looseness in the handle operation. Look underneath the engine for any sign of tears or fraying in the exposed gear cables. Replace bad cables with new ones. Grease them, before installing them into the gear cable housings connecting the engine.
Listen for grinding or clanking sounds from the engine when driving. Confirm the sounds don't occur when in idle but only when the scooter gears are in drive. With the condition verified, remove and open up the engine to locate the broken part banging around when the engine gears rotate. Replace the part and any damaged components.