The knob
settings on the Pregen (1988-2007) petcock are: OFF, ON, and RESERVE.
The OFF setting will shut the flow off completely regardless of the
engine running status. There are two intake ports on the Pregen
petcock. One is higher than the other. The purpose of this is to
provide reserve fuel that is hopefully enough to get to the nearest
gas station. The ON selection takes gas from the upper intake.
RESERVE takes gas from the lower intake. Both ON and RESERVE require
a vacuum from the engine to allow any gas to flow.
The
Newgen (2008-2012) has only one pickup at the bottom. The knob
settings are: OFF, ON and PRIME. The PRIME selection is a special
selection that bypasses the vacuum cutoff and allows gas to free flow
regardless of engine run status. PRIME is used to prime the
carburetors if they are dry. You should not run the bike when set to
PRIME. The ON and OFF selections work the same as the Newgen. There
is no RESERVE selection on a Newgen.
Symptoms
of a Bad Petcock
The most
common symptom is fuel dripping from the carburetors or the crankcase
filling up with gas. This is caused when the petcock fails to shut
off the gas when the engine is off. This can be caused by several
things. The diaphragm o-ring could be bad or the spring that pushes
it into its valve seat could be weak. Sometimes the diaphragm itself
could be bad allowing gas to leak through the vacuum port and into
the carburetor.
A less
common failure is when the petcock becomes clogged somehow and the
gas wont flow at all or at a reduced rate. This will cause a
no-start condition, a poor running condition or a situation where the
bike starts fine, but then stalls a few minutes later. The clog can
be anywhere from the intake ports to the vacuum port.
The
diaphragm itself is a very thin membrane that can tear easily. When
it goes bad, gas can be sucked into the vacuum line to the
carburetor, or you could also see gas dripping from the petcock body.
In some
cases, the rubber gasket under the knob can wear out. When this
happens, the knob selections can operate incorrectly such as the ON
position drawing gas from the RESERVE intake port or the OFF position
allowing the gas to flow.
Caution
If the
petcock has allowed gas to run into the crankcase, then you should
not run the engine until you have repaired the petcock and changed
the oil. Gasoline is a very poor lubricant and your engine could be
damaged if you run it that way.
Testing
the Petcock
To test
the petcock to see if it is operating correctly, you can do the
following procedure:
- Turn petcock to ON (with plenty of fuel in tank).
- Remove big hose. Gas should NOT come out - except for maybe a few drops that might be in the hose. There should be no continuous drip, but have a glass jar handy to catch any gas just in case.
- Remove the small hose. There should be absolutely no gas come out of the small hose and port - not even a drop.
- Attach a 3/16" diameter test hose, about two feet long, to the small petcock port.
- With your mouth (or syringe if you have one), apply suction to the small tube (again, there should be no gas in the small tube). Gas should flow out of the big tube in a nice thick stream.
- Stop applying suction. The gas should cut off.
- For Pregens, switch to RESERVE and repeat the test.
- The gas that comes out should be free from any debris. If its clear, you can pour it back into the tank.
- Lastly, switch to OFF and apply suction to the small tube. This time there should be no gas come out.
If the
petcock does not operate as described, then you need to remove it and
repair it.
Rebuilding
If your
petcock is bad, you can either rebuild it or buy a new one. I don't
recommend buying used ones because they could be just as bad as the
one you are replacing. If you rebuild, be advised that the parts
aren't cheap.
There
are some rebuild kits out there, but generally, its cheaper to buy
just the parts you need from the dealer. Be advised that the Oldgen
(1986-1987) used a different diaphragm so rebuild kits for it will
not work with the Pregen (1988-2006).
Whatever
you do, don't be tempted to use RTV to seal any part of the petcock.
RTV is not gasoline resistant and will clog up the works and/or leak.
Finally,
if you remove the petcock from the gas tank to rebuild it, be advised
that the washers on the bolts that go into the tank are special
washers that have been coated with a special gasoline proof rubber.
These are sometimes not reusable and should be replaced. If you
replace them with hardware store washers, expect them to leak. The
main petcock gasket is usually reusable, but occasionally, it has to
be replaced as well.
