Setting carb float levels is still considered a black art – but getting it right can make a significant difference to your bike’s economy and performance. Rod Gibson explains all.
So what is a float level, and why does it matter? Deep within the confines of your carburettors lurk a number of jets, whose job it is to draw in fuel, mix it with the air and send it to the engine to be burned. Those jets need to have a readily available reservoir of petrol, so each carb has a chamber fitted at its lower end that is fed with petrol from the fuel tank.
The amount of fuel in the chamber has to be controlled – too much and the surplus fuel will run out of the overflows, too little and the jets will only have air to suck in, and the engine won’t run. So far so simple, but it’s actually a bit more subtle than that, for if there’s insufficient fuel in the float chamber the bike can run weak at full throttle when there’s not enough petrol in the carb to keep up with the demands of the main jet. Conversely, having too much petrol in the chamber can make the bike run rich – but an excess of petrol usually leads to flooding problems.
To read the rest of this article, download the pdf: Setting Carb Float Levels