1
8
Check Carburetion
Before making a carburetion check, be sure the fuel tank
has an ample supply of fresh, clean gasoline. Be sure that
the shutoff valve, if equipped, is open and fuel flows freely
through the fuel line before starting engine. Inspect and
adjust the idle needle valve. Check to see that the choke
closes completely. If engine will not start, remove and
inspect the spark plugs.
If plugs are wet, look for
−
Overchoking
Plugged air cleaner
Excessively rich fuel mixture
Water in fuel
Float needle valve stuck open
If plug is dry, look for
−
Inoperative anti-afterfire solenoid.
Gummy or dirty carburetor, fuel line or tank
Float needle valve stuck shut
Inoperative fuel pump
Leaking carburetor mounting gaskets
A simple check to determine if the fuel is getting to the
combustion chamber through the carburetor is to remove
either spark plug and pour a small quantity of gasoline
through the spark plug hole. Replace the plug. If the engine
fires a few times and then stops, look for the same
conditions as for a dry plug.
Check Compression
Briggs & Stratton does not publish any compression
pressures, as it is extremely difficult to obtain an accurate
reading without special equipment.
It has been determined through testing, a simple and
accurate indication of compression can be made as
follows:
Remove both spark plugs and insert a compression gauge
into either cylinder (one cylinder at a time). Turn engine over
with engine starter until there is no further increase in
pressure. Record this reading. Repeat procedure on other
cylinder and record that reading. The difference between
both cylinders should not exceed 25%. More than 25%
indicates loss of compression in the cylinder with lower
pressure. See example.
Example:
Cyl. #1
Cyl. #2
Diff.
% Diff.
Eng. #1
65 PSI
60 PSI
5 PSI
7.6%
Eng. #2
75 PSI
55 PSI
20 PSI
26.7%
If compression is poor, look for
−
Loose cylinder head bolts
Blown head gasket
Burned valves, valve seats and/or loose valve seats
Insufficient valve clearance
Warped cylinder head
Warped valve stems
Worn bore and/or rings
Broken connecting rods
Cylinder Leakdown Test
The cylinder leakdown tester, Tool # 19545, may be used to
test the sealing capability of the compression components
of each cylinder and quickly identify the problem compo-
nent.
Cylinder Balance Test
If the engine is hard starting, runs rough, misses or lacks
power, perform a cylinder balance test to determine
whether both cylinders are operating to their full potential.
Tools Required
1. Tachometer, Tool #19200 or 19389
2. Two #19368 Ignition Testers
3. Screwdriver with insulated handle
Attach ignition tester, Tool #19368 between the spark plug
lead and each spark plug, Fig. 8.
Fig. 8
#19368
TESTER
SPARK PLUG LEAD
SPARK PLUG
Start and run engine running at top no load speed and note
spark at ignition testers. If the spark is equal at both ignition
testers, the problem is not ignition related. A spark miss will
be readily apparent. Now note RPM of engine. Ground out
one cylinder with screwdriver by contacting alligator clip on
ignition tester and a good ground on engine, Fig. 9. Note
RPM loss. Then ground out the other spark plug and note
the RPM loss. If the difference between the two cylinders
does not exceed 75 RPM, the amount of work the two
cylinders are doing should be considered equal.
TSM
Summary of Contents for 405777 Series
Page 1: ...TSM ...