Why is my air filter covered in fuel?

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Q. The fuel on my Kawasaki ER-5 is flowing straight through into the air filter box and it sounds like it is only firing on one cylinder, too.
Quilley, MCN forums

A. The ER-5 has a vacuum tap which uses a diaphragm sucked open by a vacuum via a thin black pipe from one of the inlet manifolds to allow fuel to flow when the engine is running.

It also has a prime position that by-passes the diaphragm and allows fuel to flow under gravity, for times when the carbs have been emptied – after a strip-down or when it’s run out of fuel.

It's possible for the vacuum pipe to perish and split or become dislodged, or the diaphragm to stop working. In these cases the petrol would not therefore reach the carbs.

You must have the fuel tap on ‘prime’, and if one of the carb needles has stuck or there’s a bit of crud lurking that’s holding a carb float down, that will allow fuel to well up from the float bowl and dribble into the air filter box.

If it’s been doing it for some time, say over the winter, then that fuel could have seeped down the crankcase breather pipe into the gearbox and clutch.

If it’s done that there’s a possibility that the petrol will wash all the lubricating oil off components down there and you could have a real problem.

An easy way to check this is to unscrew the oil filler cap and stick your beak in there for a good sniff, if there’s a remote whiff of petrol you’ll need to change the oil and filter too.

But before you put fresh oil in, strip the carbs down and check the floats are moving freely and as they do so, the thick little needle moves too.

A toothbrush, Q-tip and carb cleaner spray are what you need. You might find you need a new air filter and I’d be inclined to change it anyway once you’ve cleaned all the fuel out of the filter box.

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