Basic 2 Stroke Tuning Tips

TUNING TIPS-GENERAL -

Make sure machine is assembled properly and engine has passed a pressure test. It can be virtually impossible to tune an engine with an air leak. It is imperative that you establish a solid baseline with proper assembly and an air leak free engine. *Note: On a 2-Stroke engine there is absolutely no way to be sure your engine DOES NOT have an air leak without properly performing a pressure test.

- Establish that the engines compression is not weakened. Any loss of compression for whatever reason will give off signs that engines jetting is rich. Consult your service manual or engine tuner for proper compression reading. Any loss of compression on a 2-stroke engine should be followed by a top end disassembly and inspection of piston, rings, cylinder liner etc.

- Compression Test How To: Always use a quality name brand gauge (SNAP-ON Best Choice). Note length of threaded probe in relation to spark plug length. Perform test with engine cold, throttle wide open. Kick machine over until needle quits moving (10-15 kicks normal). Perform 3 separate tests, record results.

It is always a wise idea to perform a compression test on a fresh engine right after break-in to use for future reference.- Spark Plug: To properly tune a 2 or 4 Stroke engine it is imperative to have a good quality spark plug that is functioning properly. This means that the plug cannot be too old or partially fouled. Spark plug gap is essential; an improperly gapped plug (or partially fouled one) can cause the engine to run poorly, sometimes appearing to be a jetting problem when in reality the problem originates at the spark plug. Also make sure you are using the correct heat range.

- Weak Spark: Weak spark is not only detrimental to your engines performance but can make tuning your engine a nightmare. Weak spark will make the engine run rich. When an engine is running rich due to weak or poor spark the machines performance will slowly continue to deteriorate. Some common causes of weak or poor spark can be a failing or faulty stator, faulty plug cap or plug wire, failing coil, improper ground etc.

- Plug Color: Ideal plug color is a chocolate brown. A rich plug will be a darkish brown or black. May be oily and sooty. A lean plug can be a light brown, or gray (some severe cases can be white). Plug color must be checked after a plug check has been run. To perform plug check run engine at specific RPM that reading is desired for at least 5 seconds, then turn off engine without letting RPM’s fall. This test is very difficult to perform at any RPM other than wide-open throttle.

It can take years to learn how to accurately and precisely read spark plugs. For amateurs, plug color should not be the only piece of evidence used to adjust jetting. Plug reading should be evaluated with other jetting evidence to achieve a proper conclusion on tuning.

- Fuel: The fuel used in your machine is very influential in tuning your engine. Nothing jets better or more consistent than a name brand Race Fuel designed for the specific engine in question. Things to stay away from are pump fuel and aviation fuel. Both can cause inconsistent jetting feedback and make your engine run hotter than normal.

- Silencer: 2 Stroke silencers must be functioning properly. A worn out, poorly maintained, silencer can cause the engine to run funny making tuning difficult. An excessively packed silencer can also cause a tuning difficulty, making the engine lose power and run rich.

- Exhaust Pipe: Check your pipe for severe dents in head pipe section or end cone area, dents in these areas may affect tuning. Also check for carbon build up inside pipe. Any carbon build up at all is not desirable. Heavy build up will hamper engine tuning and rob power. Pipes with these problems should be replaced.

- Silencer Color: Always take note of the silencer exhaust color where the exhaust exits the silencer. Inspect the core and corresponding end cap. Colors will be similar to plug color.

- Air Filter: It is highly recommended to do your initial engine tuning/jetting with a new air filter. A used filter will never quite work as perfect as new one. Old, dirty, improperly serviced filters will severely hamper proper engine performance and tuning. When performance is critical use a new filter.

- One Change at a time: When tuning a carburetor, only make one adjustment at a time. This is a good rule to follow so the tuner will not get confused or mislead from false information. Keeping to one adjustment at a time will help ensure that you will always know what effect each adjustment had on the engine.

- Unresponsive?: If during the jetting/tuning process you have made a number of adjustments (especially main jet or needle clip) to the carburetor and the engine has not changed. There is a strong possibility that something other than carburetion jetting is causing your engine to perform incorrectly. Jetting is a constant. When adjustments are made to a machine with all components working properly the engine will respond in some way. Depending on the adjustment made the machine will either run better or worse, but there is almost always some form of change. When changes are made without any response it is a sign of other problems. Things to check out would include; low compression, weak spark, fouled plug, failing reeds, air leak, clogged air filter, clogged or over packed silencer, etc.

- Idle Adjustment: To adjust the idle on PJ and PWM model carburetors it is necessary to turn the knob on top of the choke clockwise to lower idle and counter clockwise to raise idle. PWK models are adjusted by a screw/spring approximately ¾" below the carburetor cap on the left hand side of the carburetor. Screw in to raise idle out to lower. On many models screw must be screwed in most of the way for proper idle speed. PE models also have a screw/spring that manually raises the slide. On PE models idle screw is approximately 2" below carburetor cap and perpendicular to the slide.

- Free Play: It is highly recommended that at least a ¼" of free play is kept in the throttle cable. Failure to run proper free play can cause the throttle to stick.

- Proper Slide Throw: It is always a good idea to confirm that the carburetor slide opens and closes all the way. This should be done with carburetor hooked up but off the machine, as to physically see slide travel thru its complete stroke.

- PWK Cable Holder: The cable holder on PWK model carburetor must be unscrewed to remove needle for adjustment. The only way to properly remove cable holder is with a ¼" ratchet and a 6mm socket. Turn counter clockwise to loosen. During reassembly do not over tighten. Do not put screwdriver in slot to attempt to loosen. This will cause severe damage to cable holder and slide.