Motor Trouble Shooting


Well-Known Member
Dec 13, 2015
Will it help?Not if the sky gods are against you, you still ain't got a chance.
Engine Won’t Start #1. Carburetor choke: Choke Lever up if engine is
cold, if hot; choke lever down. (NT carbs)
#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 repeatedly to clear a possible wet
flooded cylinder. Re-install plug: If no spark, go to
step #4. If spark is good and looks strong go to step
o Spark #4. Check blue and black wire connections coming
out of motor and connections to CDI. If good and
tight then remove kill wire and see if spark plug now
has spark. 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 # 5.
#5. Check magneto coil with an ohm meter. Look for
approx. 300 to 380 ohms across blue and black
wires, .25 to 3.25 ohms across white 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 # 6.
#6. Replace external CDI module. If still no spark
replace spark plug and magneto. Then repeat steps 1-
Good Spark but Engine will ot 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. Check float height and
make sure float doesn’t have any cracks. 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 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
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 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 parallel 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
Symptom Check
2-Stroke Troubleshooting Guide
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.
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