2 cycle engine trouble shooting guide
2 cycle engine trouble shooting guide
Symptom Possible causes and corrections
No Engine Start #1. Carburetor choke: Choke Lever down if engine is cold, if hot; choke lever up.
#2. Possible flooded engine: Try starting with throttle wide open. If no start go to step #3.
#3. Check spark plug; Replace if black and worn electrode is found. Check spark fire by laying spark plug with wire connected on engine head fins while fast pedaling with rear wheel held up to spin engine over at a fast rate. If spark is now good pedal spin engine over repeatatively to clear a possible wet flooded cylinder. Re-install plug: If no start go to step #4.
#4. If External CDI check blue and black wire connections. If good and tight then go to step # 5.
No Spark #4. If Integral CDI /Mag moduel remove kill wire and see if spark plug now has spark. Check for broken plug wire. Continued No spark; then replace the CDI/Mag moduel with new.
#5. Disconnect kill switch wires and try starting. If spark plug now has spark then look for an unwanted ground in the kill switch circuit. If spark plug still has no spark then go to step # 6.
#6. Check magneto coil with an ohm meter. Look for approx. 300 to 350 ohms across blue and black wires. Check for loose screws and or high corrosion. If open or shorted coils are found replace magneto coil. If magneto coil is known good and still no spark then go to step # 7.
#7. Replace external CDI module. If still no spark replace spark plug and magneto.
Good Spark but Engine will Not Start #8. Check for fuel restriction. Clean air filter: Remove line at carb. and check for fuel flow. Clean filter on tank valve. Make sure gas is not over rich with too much 2 cycle oil. 16 to 1 ratio with a brand new engine and 25 to 1 with a used engine. If Old gas replace with fresh gas/oil mix . If no start > go to step #9
#9. Possible Flooded engine: Go to step #2. If No flooded engine is found; try giving a quick squirt of starting fluid at the air cleaner opening. If engine still does not start go to step # 10
#10. Check throttle cable. Make sure it is moving slide valve up and down in carb. Still no start then go to step. #11.
#11. Check for air leaks at carburetor intake manifold tube. Check for loose manifold nuts, Check for loose carburetor and or damaged intake gasket. If not already done clean clogged or dirty air cleaner. Make sure engine does not have fuel in bottom of crankcase due to unwanted entry of drip down gas from carb with a stuck float. Remove engine and turn upside down to drain any wanted gas from crankcase and reinstall. If no start condition prevails go to Step #12.
#12. Check crankcase for possible air leaks. Check left and right oil seals on ends of crankshaft to see if correctly seated in front of bearings. Push the piston down to lowest position and plug exhaust and intake ports so you can use a hand held compression pump in the spark plug hole to see if any air escapes from crankcase. Be careful to not blow out the oil seals with too much pressure. If the crankcase gasket is leaking and needs replacing it's best to have a qualified mechanic replace the gasket. If no air leaks are found and you have a no start engine condition then go to step #13.
#13. Run a cylinder compression check by removing the spark plug and installing a small engine compression gage. Plug the exhaust and intake ports with a custom made flat plate. Use a hand held electric drill or an air wrench to turn the crankshaft at the magneto nut. Note: If the engine turns over easily with the spark plug installed or a compression gage seated in the plug hole this means you have a blown head gasket, broken rings, or a possible hole in the top of the piston. You will now need to remove the 4 head bolts and head to make further checks. Note: If compression is good and no problem is found then proceed to step #14.
#14. Replace or rebuild the carburetor and correctly set idle speed adjustment. If still you have a no start engine condition then probably it's best to consult with a qualified engine mechanic as somewhere in the trouble shooting process something has been over looked.
Engine backfires and is hard starting. Check magneto Rotor for being on backwards. With piston at Top Dead Center the crankshaft key must be at 1 o:clock position. The 2 Rotor dentures need to be in almost parrellel position with the 2 Magneto arms.. If not this way then remove the Rotor and turn it over. To learn more see the Great Magneto and Crank Mystery at www.grubeeinc.com
Engine does not reach max RPM Check for clogged muffler. Clogged exhaust port. Fuel restrictions, Low compression, Poor ignition spark, Too much oil in gas or improper air/fuel mixture in carb. Clean carb. jets and air filter; Check for a possible crankcase leak or leaking oil seal.
Engine has high rpm but no pulling power. Check clutch gear wheel for worn or greasy clutch pads. Replace worn clutch pads and adjust as required as described in owner's manual.
Engine idle is too fast or too slow Adjust idle screw air fuel mixture settings. Refer to your owners manual. Adjust cable stroke slide valve adjustment at top of carb if possible, some early made YD CNS carbs do not have this feature.
Engine has high pitched squeal Check for bent clutch rod. Check clutch adjustment. Refer to your owner's manual.
Clutch will not release With clutch engaged check for 1/16" slight free play on the left side engine clutch arm to insure correct adjustment. Remove clutch cover on right side of engine and check for possible stuck clutch plate or bent clutch rod.
Engine will not spin over when clutch lever is released while pedaling. Clutch cable may be adjusted too tightly. Check for 1/16" free play in clutch arm on left side of engine. When clutch is engaged the clutch arm on the left side of engine should be setting in an approximate parallel line up with the side of the engine. Remove clutch cover and check to see if the clutch plate is stuck open in the disengaged position.

The ETHANOL 101 Home Study Course

What you need to know about Ethanol fuel when used in small engines;

      Outdoor power equipment dealers and mechanics are finding themselves dealing with a flood of frustrated owners experiencing engines not running right or having gummed up carburetors only to bring them back a month or so later with the same complaint. What the customer does not realize is that the problem is not the engine! It’s the fuel!!!!

      The introduction of ethanol, otherwise known as alcohol, into the fuel has caused a wide range of problems. While ethanol is regarded as a fuel, blending it with gasoline results in these 4 conditions.
  • Rough idle:
  • Hard starting after leaving the engine sit idle, ( not used ), for several weeks:
  • Gummed–up carburetor jet:
  • Loss of power:
      Ethanol in gasoline breaks down and forms gums very quickly. Ethanol and Gasoline do not chemically bond with each other, instead they are held together in a loose colloidal suspension much like you would see in an oil and vinegar salad dressing mix. The fact is ordinary fuel adjustment additives developed 50 years ago and still on the market today do not correct these 4 ethanol problems.

      1. Debris in gasoline caused by Ethanol.
      Varnish Gums form in the fuel tank and in the carburetor bowl as E5, E10 & E15 ethanol fuel ages. These particles can clog Filters and Needle Jets. Modern day fuel additives break down the enzymes into sub micron sized particles that can be easily burned during the combustion process.

      2. Excessive water in the fuel and phase separation.
      Ethanol attracts moisture from the atmosphere and forms a ethanol and water mix in the gasoline. Ethanol blended fuel will naturally hold 0.5% water in separation, but when water levels exceed this threshold, or when fuel cools significantly, the water/ethanol mix drops out of suspension which is called phase separation. Excessive water in the fuel causes engines to run rough, stall and can lead to internal engine damage. A good fuel additive allows the water to mix with the fuel and get burned off to create a dried out tank result.

      3. Ethanol fuel breaks down quickly.
      As ethanol evaporates the fuel looses octane and becomes what is known as “stale”. This causes hard starts and engine rattle as well as loss of power and engine damage. A good fuel additive will enhance correction to fuel break down for up to 2 years.

      4. Ethanol causes lost power and lost performance.
Ethanol added to fuel does not allow as much energy as traditional gasoline. This results in poor engine performance. A good adjustment additive will break apart large clusters of fuel molecules, creating more surface area. This in turn allows additional oxygen to react during combustion which results in complete fuel burning and reduces toxic exhaust emission.

      The laws of some states in the USA do not require the gas station to tell you how much ethanol is in the gas they sell. E-10 or 10% is supposed to be the legal ethanol limit but up to 50% has been found in some off-brand gasoline. Adding a dry gas additive is not the answer either as these products contain more alcohol which now you know is really Ethanol and will just accelerate the problem into the realm of the third kind.
Having said all the bad news here’s some good news! There are some additives on the market that will in fact correct the short comings of having Ethanol in gasoline and will allow easy starting even after extended long periods of not running the engine. These additives must contain enzymes that allow more oxygen to bond with the fuel hydrocarbons thus allowing a more complete combustion burn of the fuel charge. This translates into these advantages. 
  • Easier Engine Starting:
  • Better throttle response:
  • Decreased exhaust emissions and decreased visible exhaust smoke:
  • Prevention of varnish gum deposits:
  • Increased fuel economy:
  • Helps prevent Phase Separation that can occur in stored fuel when water and ethanol bond together and then falls out resulting in degraded fuel that prevents good engine performance.
      The best policy is to avoid using any gasoline with Ethanol in it. We do not recommend any specific brand of additive for Ethanol correction, however here’s a list of brands making claims to have benefit;