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I am not a carburettor expert and there are many more reasons why carburettors overflow at times, but others are welcome to add their knowledge to this thread.
There are many threads on this forum on leaking carburettors especially after they have been cleaned. These leaks usually are due to leaking float needle and seats (which showed no noticeable tip wear at the time), plus a faulty petcock or an after market (non vacuum) petcock.
Disturbed rust or debris are blamed, petcocks are suspect and some are 'cured' by replacing the petcock with a new one and the underlaying fault may still be there. In many cases the needle and seats although not showing any wear are also replaced and miraculously the problem is cured! But read on...
Some of these problems are unknowingly caused by the person cleaning or rebuilding the carburettors. After 30 years the brass seat with a the little filter on the top also needs to be removed for cleaning and replacing the o-ring around it.
The method advised and used is to grip the brass seat with a pliers and just pull it out. Some can be stuck and need quite a bit of force, the pliers then distorts the rear end of the brass seat and the inner clearance that allows free up and down movement of the needle is compromised. Due to the needle being triangular it may not be noticeable in some positions and in others it may stick closed or open, causing the float bowl to overflow or to run dry.
A special tool is needed to remove these or a new drill bit (chuck side, no burrs) that fits snugly in the opening to limit such distortion and some overnight penetrating oil beforehand can be used. Penetration oils will not seep past the o-ring and loosen it!
In the case of actually damaging the seats, it would only be the rear (open end) and some carefull hand reaming with 1200 sandpaper wrapped around a hex key can easily correct this. Testing can be done by using the above mentioned drill bit.
Otherwise budget to replace all four of them to be safe!
Hope this helps some out there.
There are many threads on this forum on leaking carburettors especially after they have been cleaned. These leaks usually are due to leaking float needle and seats (which showed no noticeable tip wear at the time), plus a faulty petcock or an after market (non vacuum) petcock.
Disturbed rust or debris are blamed, petcocks are suspect and some are 'cured' by replacing the petcock with a new one and the underlaying fault may still be there. In many cases the needle and seats although not showing any wear are also replaced and miraculously the problem is cured! But read on...
Some of these problems are unknowingly caused by the person cleaning or rebuilding the carburettors. After 30 years the brass seat with a the little filter on the top also needs to be removed for cleaning and replacing the o-ring around it.
The method advised and used is to grip the brass seat with a pliers and just pull it out. Some can be stuck and need quite a bit of force, the pliers then distorts the rear end of the brass seat and the inner clearance that allows free up and down movement of the needle is compromised. Due to the needle being triangular it may not be noticeable in some positions and in others it may stick closed or open, causing the float bowl to overflow or to run dry.
A special tool is needed to remove these or a new drill bit (chuck side, no burrs) that fits snugly in the opening to limit such distortion and some overnight penetrating oil beforehand can be used. Penetration oils will not seep past the o-ring and loosen it!
In the case of actually damaging the seats, it would only be the rear (open end) and some carefull hand reaming with 1200 sandpaper wrapped around a hex key can easily correct this. Testing can be done by using the above mentioned drill bit.
Otherwise budget to replace all four of them to be safe!
Hope this helps some out there.
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