Questionmy honda fourtrax is sputtering when i hit the throttle and the carb is good and clean all spark plugs are new so i dont know what it is.
AnswerHello William,
The number one cause for sputtering is
moisture in the fuel tank.
If even one drop of water forms inside
the tank it can plug up the carbs jets
instantly.
Remove the fuel petcock valve
from the tank and check the screen is clean
and the rubber seals are usable.
Then install the petcock valve and
add some fresh fuel.
Open the drain on the carb float bowl and
let some new fuel run through.
Close the drain and run it a bit with the
new fuel. See if that helps.
Then run it awhile at the sputtering speed
with a clean spark plug.
Stop the engine quickly.
Do a plug reading to find out what the
fuel mixture is like.
Refer to this chart:
http://verrill.com/moto/sellingguide/sparkplugs/plugcolorchart.htm
If the spark plug is black then check the air filter.
If the plug is light colored you may have an air leak
around the carb or intake tube.
If the plug is oily then check if the engine compression
is low, under 120 psi. Maybe it needs a minor rebuild.
If the plug is a light tan or brown color
as in the chart then it may be just some dirt
or water has entered the carb from the fuel tank.
Changing carb jets is a last resort as it can
damage the engine unless the spark plug color
is observed closely.
The main jet is the one in the carbs center and
controls high speed fuel. Smaller is less fuel.
The needle in the carb slide can be lowered to
lean the fuel and raised up to increase the fuel
at mid throttle openings.
Spark plug caps should have about 5000 ohms resistance.
Use the proper spark plug and I recommend NGK brand.
Luck!
Wayne S
----------------------------------------------------------------
