;
Install the rubber block off plate between the muffler gasket and the engine and
install a flange adapter in place of the carburetor. Be sure to block the impulse
hose.
;
When checking the crankcase for leaks, pressurize the crankcase to a reading of
positive 0.5 bar, or about 7 pounds per square inch. The pressure should not leak
down to positive 0.3 bar, or about 4 pounds per square inch, in 20 seconds. If it will
not hold pressure or leaks down too fast, locate the leak with a soapy water
solution.
To perform a crankcase pressure and vacuum test the intake port and exhaust port must
be sealed with the proper blocking tools.
STIHL 4-MIX
®
engines need to also have the
valve cover installed.
Gauge readings.
;
If the crankcase holds pressure, then apply a vacuum of negative 0.5 bar, or about
negative 7 pounds per square inch. The vacuum reading should not leak to above
negative 0.3 bar, or about negative 4 pounds per square inch, in 20 seconds.
;
If the engine has a vacuum leak, but no pressure leak, the fault is most likely a
crankshaft seal. Expose each seal and position the engine with the seal facing up,
spray some light penetrating lubricant on the seal around the crankshaft and apply
a vacuum with the tester to see if any of the liquid is sucked into the seal.
Vacuum
Range
Pressure
Range
Impulse Line
Check impulse line for blockage.
;
One method to check the impulse is to use a small carburetor pressure tester, and
hook it to the impulse hose.
;
When you pull the starter rope, the needle on the gauge should bounce back and
forth indicating positive and negative pressure. If nothing happens, the impulse
line or impulse passageway is restricted.
