A leakdown test is performed by introducing air pressure to the
cylinder when it is at TDC on the compression stroke. If a wrench
is used on the crankshaft end to turn the engine, it is necessary
for someone to hold the wrench when the test is being performed.
Failure to do so can result in the wrench turning and causing
possible injury. If the bike is in gear when the test is performed,
someone must hold the brake, or the bike can move when air is
Performing the test is very simple. Bring the cylinder to be
tested to top dead center on the compression stroke. Insert the
appropriate adapter hose in the spark plug hole and just snug
it against the o'ring. Do not over tighten. Plug the adapter
hose into the right hand side of the tester. Turn the yellow
knob on the regulator counter clockwise fully and plug in an
air supply with at least 120 lbs pressure. Failure to turn
the regulator down before hooking the air supply can result in
damage to the regulator. We do not replace any damaged regulators.
With the air supply hooked up, turn the yellow knob clockwise
until the pressure on the left gauge reads 100 lbs. If the engine
is in perfect condition, the right gauge will also read 100.
Anything less is the amount of leakdown that cylinder has. Example.
If the right gauge reads 90 psi, that cylinder has 10% leakage.
80 lbs, 20% leakage, etc. 2-3% is usually considered "very
good" If the leakage is 10% or more than you should be
able to hear it. Listen in the carbs or air box with the throttle
open. If you hear air escaping, it is an intake valve. Listen
in the exhaust pipe for bad exhaust valve. In the oil filler
means bad rings, etc.