increments) and rev the engine after each adjustment. To lower the idle, turn the
screw counter-clockwise.
TOP END JETTING:
Indications that the engine is running too rich (too much fuel for the air) are:
Engine not revving out or blubbering at high RPMs.
Engine will not ‘clean out’
Wet or black spark plug
NOTE: Before changing jetting be sure that the air filter is properly cleaned and
has the usual amount of air filter oil. An overly dirty air filter can cause the engine
to run rich.
If the engine is running rich on the top end it should be leaned out. Leaning it out
can be done by:
1. Changing the main jet to a smaller number.
2. Raising the needle clip (this lowers the jet needle) one notch at a time on the
slide.
Indications that the engine is running too lean are:
Engine cutting out on top end.
Engine overheating and ultimately seizure.
White spark plug
CAUTION:
It is much safer to operate the engine slightly rich as opposed to slightly lean.
This is because an overly rich engine will just run poorly while an overly lean
engine will seize, potentially causing an expensive top end rebuild and a DNF.
To richen the carburetor:
1. Change the main jet one number at a time (larger).
2. Lower the needle clip (raising the jet needle) one notch at a time until the
engine starts to blubber on the top end, then move the clip back up one notch
or until you get the blubber out.
FUEL MIXTURE SCREW
The left side brass screw is a fuel mixture (air) screw. This screw will also richen
and lean your engine more on the bottom and mid-range. In warmer conditions,
turn the screw in. In colder conditions, turn the screw out. Be sure to keep the
carburetor very clean and make sure you don't have water or dirt in the
carburetor bowl. Use automotive carburetor cleaner or WD-40 to clean the
carburetor inside and out. Turning the screw in richens the mixture at partial
throttle openings. Turing the screw out, leans it.
Cleaning the carburetor:
Clean the carburetor in a well-ventilated area, and take care that there is no
spark or flame anywhere near the working area; this includes any appliance with
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