Fixing Dripping Carbys on an Airhead

Symptoms?

I have an R80 G/S that has suffered from fuel leaking from the carburettors. There are many possible causes of this, some have been treated else where but not all of them brought together. So here it is - all of them, seven in total. If you have a cause that is not listed here then I want to know about it!

Finding the cause

Turn off the fuel.
Remove the float bowel on the carby that is leaking the most.
Look at the fuel in the float bowel.

If there is no dirt or water in the bottom of the float bowel then go to the next section titled "Clean Fuel".
If there is dirt in the bottom of the float bowel then go to the second next section titled "Dirty Fuel". Water - well you wash the bike too much? - go to the next section.
Note that the observation is subjective and you may not see the bit of dirt doing the damage... or the dirt may be let over and not the real cause of the problem.

Clean Fuel

OK - possible causes

Needle has worn, gone hard (the rubber tipped variety) or needle seat scored. Check that raising the float / needle actually shuts off the petrol
Float sinks in the petrol - check that the float does actually float in petrol
Float bowel gasket faulty - replace it
Float sticking - either on the pivot pin, or on the sides
Float tang worn by needle so that needle sticks - smooth the tang
Dirt between the needle and seat... see the "Dirty Fuel" section next

The easy one first - empty the float bowel you have removed, then hold it under the carby. Turn the fuel on, and check it is now flowing out of the carby, push the float up and check that the fuel shuts off. Turn off the fuel from the tank before the float bowel overflows, empty it back into the fuel tank and repeat. Check for dirt in the discharged fuel, no dirt means you are in the right section. If the fuel does not shut off then you have found the problem. For some reason the needle and seat are not sealing. Check that jiggling the float does not clear the problem. If jiggling works look at the needle valve for ware, tang for ware marks from the needle.
The other possiblity here is the needle seat itself is worn. Good luck with this, I've only had one report of this.
If the needle and seat are working then you need to check that the float floats in petrol. Simple enough. Some people say the styrofoam looking floats are not good with modern fuels, my 1981 model styrofoam floats still work... maybe I only get old fuel? New floats are hollow black plastic? I remember the hollow brass floats that were soldered together, a pin hole leak is all that is needed to sink the old brass floats.
If none of the above are the problem then may be the float is getting caught on something, possibly the gasket, sides of the bowel or the pivot pin. Good luck.

Dirty Fuel

I Think this is the most frequent cause. OK - the source for the dirty fuel is your fuel tank. Either that or the fuel hose is deteriating or if equiped the fuel filter/s then they are. Simply cleaning out the fuel in the float bowels may finish this trip, but you need to clean out the system. If the source is the fuel hose or filters then replace them. If not then I hopefull your fuel tank is not rusting. Remove all the fuel from the tank, you need somewhere to put it, and it may come out dirty, filter it in some way. I let it settle in an ice cream container, the dirt goes to the bottom. Empty the clean fuel into a jerry can and repeat untill you have only half a container full and nothing in the bikes fuel tank. Now remove the fuel petcocks. There should be fine copper screens on top of the petcocks, if not take a look at the tank and see if you can find them. Clean the petcocks and screens in the petrol. Done? Well you will still have dirt in the tank! You need to poor the clean petrol into the tank and let that drain out into another container, it will come out dirty! Repeat this untill it comes out clean. Take a look as to why all this dirt was inside, fuel tank not rusting? Paint not seperating from the inside of the tank? If it is rusting or the paint eperating then you need something like "Kreem", a fuel tank inner paint. Go see your local expert, or do a web search. Reassemble, you might like to include an external fuel filter in your system to stop the dirty fuel getting to the carbys. Note that the 'dirt' could come from some petrol station. Take a look at the petrol you get when filling your bike.

Why does only one carby leak when the cause is dirty fuel?

Well you only use one petcock at a time, or one side of the tank is dirty, the other clean. The dirt is heavy and flows downwards, so a "T" piece may send the petrol in 2 directions but the dirt will go to the lower side. So only one carby will tend to collect the dirt. However if you do find dirt in one side, clean both sides to avoid doing the second side later.

Most of my leaks have been dirty petrol, but then mine is a G/S travelling in remote places where fuel can come out of a 44 gallon drum by hand pump.

You can e-mail me at Yahoo. Back to my home page Dated 30 March 2002