So your old petcock is leaking...

For many of the petcocks on these old bikes, you can buy petcock repair kits, or some of the key components to repair your petcock.  The repair kits vary in what is included from a small number of o-rings, to a comprehensive bag of parts. 

Make sure the petcock kit is for your petcock.  One of the challenges with 20-30 year old bikes is many parts get swapped out over the years - so it is best to try and visually assess whether the parts in the kit match the shape and style of your petcock.  Additionally, some of the OEM (Original Equipment Manufacturers) modified designs part way though a year - in these cases it is very difficult to be sure parts will fit.

Generally, there are two main types of petcock - manual and vacuum.  With the manual petcocks, you have to select between off, on and reserve.  With vacuum petcocks the choice is prime, on or reserve.  These vacuum petcocks are 'opened' by a vacuum hose leading from the carbs.  Once a suction is produced in the tube by the engine running, it opens the petcock and fuel flows.  Prime is used to initially fill the carbs and after that should not be used

Will the repair kit fix my leak?

Generally, the kits fix 50%-75% of the petcock problems.  Unfortunately wear inside the petcock is not confined to rubber o-rings and diaphragms - often the problem is wear in the form of scrapes and gouges caused by rust particles making their way into the petcock and acting as a grinding paste when the lever is moved.  Additionally, corrosion inside the petcock causes a deterioration in the cast metal of the petcocks and no amount of changing o-rings and diaphragms can compensate for these problems.

"I give up, my petcock is never going to work properly - now what?"

Several options exist to replace leaky petcocks.

In some cases complete replacement petcocks are available for bikes, but in many cases you have to choose from a variety of aftermarket 'generic' petcocks and adapter plates/nuts.  This means knowing whether you have a vacuum style petcock or a manual version, and know how many fuel feed nipples come from the petcock. 

Just make sure you do not confuse a vacuum hose for a fuel hose.

There are limited choices to replace vacuum petcocks, on most bikes you can replace the vacuum petcocks with a manual petcock providing you cap (block) the vacuum feed from the carbs (this is crucial as leaving the hose open WILL cause a lean condition with the risk of holing a piston)

Fitment varies from make-to-make and model-to-model.  Generally they are either threaded on (bung style), or bolted on. 

With threaded, you need to know the diameter of the thread to determine petcock choices - 22mm is found on Kawasaki 900 & 1000 motorcycles from the 1970's.  The example to the right is a Pingel single-outlet petcock with 22mm threaded nut and the outlet nipple pointing backwards across the motorcycle.  To measure you get a reading across the thread - expect the reading to be slightly smaller than the size stated on the petcocks.  For example 22mm will measure 21.87mm with a dial caliper.

With bolt-on, the majority are similar in design, but the bolt-to-bolt spacing varies considerably.   You will need to measure from bolt center to bolt center to know what will fit your bikes fuel tank.  Generally most bolt-to-bolt spacing is 34mm, 44mm, 46mm or 50mm.  The example to the left is a vacuum style petcock with a single outlet nipple pointing  to the side.

Be advised that some of the aftermarket petcocks come with a larger diameter filter than stock and different shapes - this means you MAY have to enlarge the hole in the tank for the filter to fit or remove the filter.  Additionally, the length of the main feed pipe going into the tank may be different from stock, so the reserve capacity may / will change.

Do not forget to consider the direction of the fuel feed nipple leaving the petcock.  Most come out the back - but some come out the sides.  It is very important to make sure fuel hose is routed AWAY from the engine and is not touching hot engine components.

Pingel adapter plates - Pingel makes a variety of adapter plates that allow 3/8" NPT threaded petcocks to be used on a variety of tanks.  You do not have to use Pingel petcocks with the adapter plate, just petcocks with a 3/8" NPT thread.  Pingel also makes offset and blank adapter plates for custom applications.

NPT thread is National Pipe Taper thread, this is a tapered thread that tightens the further you thread the male Petcock into the female adapter plate.

Pingel adapter nuts - Pingel makes a number of different thread size adapter nuts that allow 1/4" NPT threaded petcocks to be used on a variety of tanks.  You do not have to use Pingel petcocks with the adapter plate, just petcocks with a 1/4" NPT thread. 

If your carbs have dual fuel hose feeds, you can use a Y or T 'splitter' to feed both sides.  Fuel flow through the aftermarket single outlet petcocks IS sufficient to put a Y or T 'splitter' in the hose on all but the radical larger cc motorcycles (many stock 1000cc motorcycles use only one fuel feed to supply all four carbs)

One last consideration is fuel flow.  Most of the aftermarket petcocks will flow enough fuel for street use.  However, if you have high-performance parts in the engine, you should look at the Pingel fuel valves as they 'pass more gas'...

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