STARTING DIFFICULTIES

Ossa's are known for quick starting even under conditions where they are raced regularly, but exceptions can occur.
If your machine is consistently hard to start, check the fuel petcocks.  Some petcocks will allow a dribble of fuel to get into the engine even when shut off and thus cause very difficult starting.  Pull off the fuel line at the petcock and wipe the petcock outlet dry with a rag.  Wait a few moments and check for any seepage of fuel.  If you can find better petcocks, install them; if not, pull the gas lines off at the petcocks each time the engine is shut off.

As with any high-performance two stroke, the spark plug must be clean and of the correct beat range to start the engine.  Your Ossa dealer can recommend the heat range best for the type of riding you do.  If the bike doesn't start after repeated kicking, remove the plug and dry it if wet or replace with a spare one. On Pioneer models, check that the battery is fully charged by beeping the horn or turning on your lights and recharge if necessary.

Refer to Chapter Three for detailed engine timing procedures and Chapter Five for step-by­step troubleshooting of the electrical system.  The Ossa uses an electronic ignition system without points. If the bike has just been washed and won't start, water may be shorting the spark plug wire or may have gotten into the air cleaner box and fouled fuel through the carburetor.  Buy and install a waterproof spark plug cap available from your dealer.  If water can be seen on the inside of the air cleaner box be more careful when washing the bike or use strips of naugahyde or similar material to make a shield around the larger openings.

If a healthy spark occurs at the right time and there is an adequate flow of gas to the carburetor, check the carburetor itself at this time.  Make sure all jets and passages are clean.  If your Ossa is raced, especially in motocross, the carburetor flat level must be checked at least monthly.  Refer to Chapter Four for specifications.
Check that the carburetor is mounted snugly and no air is leaking past the intake manifold.  Check that the air filter is not clogged.

You can get a rough idea of ring, piston, and cylinder wall condition by operating the kick starter slowly by hand and noting the resistance felt.  Some familiarity with engine service procedures is necessary to correctly interpret results from this test.  The spark plug can be removed and a finger placed over the plug opening while the engine is turned over to gauge approximately how much compression is being produced in the cylinder.  Little or no pressure will indicate broken rings or piston. An accurate compression check will give a much better idea of the condition of the basic working parts of the engine.

 A compression gauge is needed for this test. With the engine warm, take out the spark plug and clean away any dirt or grease around the spark plug bole.  Insert the tip of the gauge in the bole and hold it securely in place.  With the throttle fully open, crank the engine over several times by hand.  The gauge should read around 125 psi.  A low reading indicates service will be needed for the rings, piston, or cylinder bore.  Your dealer is equipped to check crankcase seals by performing a pressure check.

POOR IDLING

Poor idling may be caused by incorrect carburetor adjustment, incorrect timing, or ignition system defects.  Check the gas cap vent for obstruction.  Leaking crankshaft seals may cause poor idling and severe power loss.

MISFIRING

Misfiring can be caused by a weak spark or dirty spark plug.  Check for fuel contamination. Run the machine at night or in a darkened garage to check for spark leaks along the plug wires and under the spark plug cap.  Any leaks will show up vividly.
If misfiring occurs only at certain throttle settings, refer to Chapter Four for carburetor adjustment and service.  Misfiring under heavy load, as when climbing hills or accelerating, is usually caused by a malfunctioning spark plug.