Engine Model:
Briggs & Stratton
Classic,
450 and 500 Series
Page
17 of 32 B&S Classic, 450 and 500 Series Selfhelp
Guide 2011, Issue 1.0
6 Engine Cutting Out or Running Unevenly
QUICK TROUBLESHOOTING GUIDE:
Problem: Likely
Cause:
Solution:
Engine runs
briefly and stops
•
Engine is starting with the
petrol from pressing the primer
bulb, but diaphragm not
engaging and feeding petrol
•
Change
diaphragm
(refer to a dealer or
see A for instructions)
Engine revs are
very low
Engine hunts
continuously
•
Air filter needs cleaning or the
diaphragm is not feeding the
petrol evenly
•
Diaphragm is not feeding the
petrol evenly
•
Clean the air filter, and
(if necessary) change
diaphragm (refer to a
dealer or see A for
instructions)
•
Change
diaphragm
(refer to a dealer or
see A for instructions)
Diaphragm has
been changed,
but with no
improvement
•
Poor seal (not air-tight or dirt
trapped) between the petrol
tank and the diaphragm
•
Repeat the work
ensuring the tank is
thoroughly clean
where the diaphragm
sits. Otherwise, refer
to a service dealer.
Primer bulb has a
hole in it
•
Mice sometimes chew a hole
in the rubber primer bulb over
the winter period
•
Replace the primer
bulb (see B or refer to
a service dealer.
A: Changing the Diaphragm:
These engines do not have a petrol pump. They have a
DIAPHRAGM
.
When the
diaphragm is ready to be replaced (typically after some 18 months’ use) it leaks air,
and feeds petrol unevenly to the engine causing it to “hunt” (i.e. run unevenly in
surges). This is accompanied by black smoke (excess petrol being burned off) and
an increase in petrol consumption.
The diaphragm can be replaced by an authorised Briggs & Stratton dealer.
This is a chargeable job and NOT a warranty repair.
If a user has a mechanical or practical nature they can buy the part from the dealer
and fit it themselves. If doing this work oneself it is essential to:
•
Work cleanly and ensure no dirt is introduced into the work, and
•
Not stretch or distort the springs in the throttle mechanism behind the air
cleaner
The task has 4 separate stages:
1. Remove the carburettor and fuel tank.
2. Separate the carburettor and fuel tank.
3. Replace the diaphragm and gasket.
4. Re-assembly.
