2 Stroke Trouble Shooting Guide

Having problems with your 2 stroke bicycle engine? Rest assure, by following this trouble shooting guide, you'll be sure to be back on the road in no time!

Symptoms Check

Engine Won't Start


Carburetor choke: If engine is cold, ensure that the choke lever is up. If engine is hot, ensure that the choke lever is down.


Possibly flooded engine (Excess fuel inside engine): This can occur if fuel valve is left open while engine is off for long period. Turn fuel to off position and try starting engine with throttle wide open. In some cases, it is required to remove spark plug and allow fuel to evaporate over night.


Check spark plug: Replace if black and worn electrode is found. Check if spark is being generated from the spark plug. To check: remove spark plug from head of engine and leave connected to the CDI. Ground the spark plug by making contact between the spark plug and the cylinder fins, turn the engine over by spinning rear wheel and inspect to see if spark is generating from the spark plug. If spark is present: Reinsert spark plug into cylinder, turn fuel valve to OFF position and turn engine over repeatedly to clear a possible flooded cylinder. If engine still does not start, go to step #8.  If spark is not present: Proceed to step #4.

Video Instructions Here- Checking Spark

No Spark


Check blue and black wire connections coming from motor to the connections to CDI module. If secure and tight, remove kill switch wire completely and see if spark plug now has spark. To check for spark, remove spark plug from head of engine, with spark plug making contact with cylinder fins, spin rear wheel and see if spark is generating. If spark plug now has spark, inspect kill switch wires for an unwanted ground. If spark plug still has no spark, proceed to step #5.


Check magneto coil with an ohm meter. Set Ohms meter to 2K or 2000 setting. Place Ohms meter positive and negative contacts to contact points on top of magneto. Ohms meter reading should read 300 to 380 ohms across the blue and black contact points. Also check for loose contacts and/or high corrosion. If open or shorted magneto coil is found, replace magneto coil. If magneto coil is good, it is possible that the magneto is not properly grounded to the engine due to the epoxy coating on the magneto. Using fine grit sand paper, lightly sand the underside of the magneto before re-installing the magneto. If still no spark proceed to step #6.

Video Instructions Here- Ohms Testing

Video Instructions Here- Improving Magneto Contact Point

Good Spark but Engine Will Not Start


Replace external CDI module. If still no spark, replace spark plug and magneto. Then repeat steps 1-6.


Check for fuel restrictions. Clean air filter: Remove fuel line on carburetor and check for fuel flow. Clean filter on tank valve. Make sure gas is not over rich with too much 2 cycle oil. Please check your user manual for proper oil:fuel ratio. If engine still does not start, proceed to step #8.


Possible flooded engine: Follow instructions in step #2 above. You can also try to give a squirt of starting fluid at the air cleaner opening. If engine still does not start, proceed to step #9.


Check throttle cable. Make sure the throttle cable has tension and is moving the slide valve up and down inside of carburetor. If engine still does not start, proceed to step #10.


Check for air leaks at carburetor intake manifold tube. Check for loose manifold nuts, check for loose carburetor on intake manifold, check for damaged intake gasket. Check float by removing float bowl from the bottom of the carburetor. Inspect float for any cracks or holes. Check float bowl height, if float bowl height is too low, fuel will not enter the engine properly; if float bowl height is too high, too much fuel will enter the engine. Adjust float bowl plunger fork to adjust height of float. If engine still does not start, proceed to step #11.


Check cylinder compression. (Very rare issue unless engine has been used extensively over many years).- Inspect top and bottom head gasket for any leaks. Remove top four cylinder studs, check for broken piston rings, heavy scouring on cylinder wall or hole in the top of the piston. If cylinder compression is good and engine still does not start, proceed to step #12.


Check crankcase for possible air leaks. (Very rare issue unless engine has been used extensively over many years). Check left and right oil seals on end of crankshaft to see if seals are correctly seated in front of bearing. Put the piston down to the lowest position and plug exhaust and intake ports. Using hand held compression pump in the spark plug hole to see if any air escapes from the crank case. Be careful to not blow out the oil seals with too much pressure. If the crankcase gasket is leaking, replace the gaskets. If no leaks are found and your engine still does not start, proceed to step #13.


Replace or rebuild the carburetor and correctly set idle speed adjustment. If the engine still does not start, it is best to consult with a qualified small engine mechanic as somewhere in the trouble shooting process, something has been overlooked.

Engine Does Not Reach Max RPM


Make adjustments to the carburetor air/fuel ratio (where applicable- some models are non-adjustable). See Video Instructions. Check the following: Clogged muffler, clogged exhaust port, fuel restrictions, low compression, poor ignition spark, too much oil in gas or improper air/fuel mixture in carburetor. . Clean carburetor jets and air filter.

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 the owner's manual. See Video Instructions.

Engine Idle is Too Fast or Too Slow


Adjust idle screw air fuel mixture settings. Refer to your owners manual. Adjust throttle cable slide valve at the top of the carburetor and at throttle handle to ensure the throttle cable tension is not too loose or too tight.

Engine Has High Pitch Squeal


Check clutch gear wheel for overtightened clutch gear assembly or worn or greasy clutch pads. Make adjusts as required.  See Video Instructions.

Clutch Will Not Release


Check to see if clutch arm on left side of the engine has enough tension. The clutch arm should not be completely parallel to the engine block. Clutch arm should be turned into 10 degrees at resting (engaged position). Ensure that when the clutch lever is pulled, the clutch arm is moving past the engagement point. If clutch still does not disengage, remove the clutch cover on the right side of the engine and check for possible stuck clutch plate. If clutch plate is stuck. While depressing the clutch lever, apply strong downward force to the rear wheel and jolt the bike back and forth to release the stuck plate.

Engine Will Not Spin Over When Clutch Lever is Released While Pedaling


Clutch cable may be adjusted too tightly. Check to see that the clutch arm on the right of the engine is not turned too far in at resting (engaged position). It should be resting at no more than 10 degrees at resting position. Ensure that when the clutch lever is released, it is moving past the disengagement point. After making this adjustment, if clutch still does not engage, the clutch pads may be worn and require tightening. Remove the clutch cover, adjust and tighten the clutch per operating manual instructions.

Engine Backfires and is Hard Starting


Check magneto rotor for being on backwards. With the piston at Top Dead Center, the crankshaft key must be at the 1 o'clock position. The 2 rotor dentures need to be in an almost parallel position with the 2 magneto arms. If not it is not positioned this way, remove the rotor and turn it over.