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Float Level Setting


Correct setting of the float level is essential if the engine is to run well with good fuel economy.  If the float level is wrong it can make starting difficult and lead to very poor mpg figures.  All carburettor tuning should start with ensuring that the float level is correct.


The Workshop Manual talks of setting the level by measuring the gap between the lid of the float chamber and the bent down the portion of the fork against which the float pushes.  The problem with this method of checking is that it assumes that all floats have the same buoyancy.  In practice some floats float higher than others so a setting method which looks at the actual petrol level is needed.


Fortunately it is quite easy to see the actual level of the petrol in the carburettor.  Remove the dashpot and the piston holding the needle and put these in a safe place, somewhere where the needle cannot get bent. Now look down into the carburettor and you will see the top of the jet with the small hole (90 thou.) into which the needle fits.  You will also see the top of the guide in which the jet slides.  If you pull out the choke so that the choke lever pulls the jet head down, you will see the jet slide down the guide.  Make sure that the choke is working properly and that the jet slides down to its full extent.


With the choke fully in, pump up the petrol into the float chamber until it is full and look down into the carburettor and note the level of the petrol in the jet guide.  It should be below the top of the jet.  Now pull the choke right out and check the petrol level again.  This time it should be level with the top of jet or slightly above.


If the level is too high or too low,  bend the float lever a little at a time until the correct level is obtained making sure that the flat part of the lever which pushes the needle valve remains flat.


If two carburettors are fitted repeat this process on the other one.  You can now go on to synchronising the carburettors and adjusting the mixture.