Starting Difficulties; Fuel Mixture; Compression; Ignition - Wisconsin vg4d Repair Manual

2. Good compression in the cylinder.
3. Good spark, properly timed, to ignite the mixture.
If all three of these conditions do not exist, the en-
gine cannot be started. There are other factors which
will contribute to hard starting; such as, too heavy a
load for the engine to turn over at a low starting
speed, a long exhaust pipe with high back pressure,
etc. These conditions may affect the starting, but do
not necessarily mean that the engine is improperly
adjusted.
As a guide to locating any difficulties which might
arise, the following causes are listed under the three
headings:
Fuel Mixture, Compression, and Ignition.
In each case, the causes of trouble are given in the
order in which they are most apt to occur. In many
cases the remedy is apparent, and in such cases no
further remedies are suggested.
STARTING DIFFICULTIES
FUEL MIXTURE
No fuel in tank or fuel shut-off valve closed.
Fuel pump diaphragm worn out, so pump does not
supply carburetor with fuel.
Carburetor not choked sufficiently, especially if en-
gine is cold. See 'Choke', Page 8.
Water, dirt; or gum in gasoline interfer:ing with free
flow of fuel tc carburetor.
Poor grade or stale gasoline that will not vaporize
sufficiently to form the proper fuel mixture.
Carburetor flooded, caused by too m u c h choking,
especially if engine is hot. See "Chol~e', Page 8,
Dirt or gum holding float needle valve in carburetor
open. This condition would be indicated if fuel con-
tinues to drip from carburetor with engine standing
idle. Often tapping the float chamber of the carburetor
very lightly with the wood handle of a screw driver or
similar instrument will remedy this trouble. Do not
strike carburetor with any metal tools, it may cause
serious damage. Also if the mixture in the cylinder,
due to flooding, is too rich, starting may be accom-
plished by continued cranking, with the carburetor
choke open.
If, due to flooding, too much fuel should have entered
the cylinder in attempting to start the engine, the
mixture will most likely be too rich to burn. In that
case the spark plugs should be removed from the cyl-
inders and the engine then turned over several times
with the starting crank, so the rich mixture will be
blown out through the spark plug holes. The choke
on the carburetor should of course be left open during
this procedure. The plugs should then be replaced
and starting tried again.
To test for clogged fuel line, loosen fuel line nut at
carburetor slightly. If line is open, fuel should drip
out at loosened nut.
COMPRESSION
Compression check with a commercial compression test gauge
can show whether or not an engine has faulty compression. TYP
does not consider it practical to publish a PSI compression figure
because of the variables involved: engine condition, method of
testing, and RPM of test. Our recommendation is that whatever
gauge test is performed, a 10% variance between cylinders would
indicate leaking rings, leaking valves or any of the following:
Cylinder dry due to engine having been out of use for some time.
See 'Restoring Compression', Page 15.
Loose spark plugs or broken spark plug. In this case a hissing
noise will be heard when cranking engine, due to escaping gas
mixture on compression stroke.
Dzunaged cylinder head gasket or loose cylinder head. This will
likewise cause hissing noise on compression stroke.
Valve stuck open due to carbon or gum on valve stem. To clean
valve stems, see "Valves', Page 22.
Valve tappets adjusted with insufficient clearance under valve
stems. See "Valve Tappet Adjustment', Page 24.
Piston rings stuck in piston due to carbon accumulation. If rings
are stuck very tight, this will necessitate removing piston and
connecting rod assembly and cleaning parls. See "Piston and
Connecting Rod" Page 21.
Scored cylinders. This will require reboring of the cylinders and
fitting with new pistons and rings. If scored too severely, an
entirely new cylinder block may be necessary.
IGNITION
See ',tlagneto Ignition Spark' Page ll or 'Distributor-
Battery Ignition', Page 1.3. No spark may also be at-
tributed to the following:
Ignition cable disconnected from magneto or spark
plugs.
Broken ignition cables, causing short circuits.
Ignition cables wet or soaked.
Spark plug insulators broken.
Spark plugs wet or dirty.
Spark plug point gap wrong. See Page I5.
Condensation on spark plug electrodes.
Magneto or Distributor breaker points pitted or fused.
Magneto or Distributor breaker arm sticking.
Magneto or Distributor condenser leaking or grounded.
Spark timing wrong. See 'llagneto Timing', Page 12,
or 'Distributor-Battery Ignition', Page
ENGINE MISSES
Spark plug gap incorrect. See Page 15.
Worn and leaking ignition cables.
Weak spark. See 'llagneto Ignition Spark', Page II,
or 'Distributor-Battery Ignition', Page 13.
17