Dellorto main jets fit all Dellorto carburettors and replicas. The following sizes are used in the individual carburettors:
12 mm - 17.5 mm / 6 mm Jet size
19 mm - 24 mm / 5 mm Jet size
From 25 mm on / 6 mm main jet
The jets also fit the standard Mikuni carburettors on CPI or Keeway scooters.
A change in the main jet is most crucial when fitting an aftermarket exhaust or a 70cc overbore kit. It is generally a good idea to increase the jet size by 10-15 % with sports exhausts or 70cc overbore kits. This is however only a recommendation. Always start the tuning process with an oversized main jet. If the engine starts to stutter, the engine is running too rich and you should jet down incrementally until the engine runs smoothly. A good sign that the main jet is correct is the colour of the spark plug.
Light brown = Ideal
Dark to black colouration = mixture is too rich (main jet is too big)
Grey to almost white = mixture is too lean (main jet is too small) and there is a danger of seizure or other engine damage.
12 mm - 17.5 mm / 6 mm Jet size
19 mm - 24 mm / 5 mm Jet size
From 25 mm on / 6 mm main jet
The jets also fit the standard Mikuni carburettors on CPI or Keeway scooters.
A change in the main jet is most crucial when fitting an aftermarket exhaust or a 70cc overbore kit. It is generally a good idea to increase the jet size by 10-15 % with sports exhausts or 70cc overbore kits. This is however only a recommendation. Always start the tuning process with an oversized main jet. If the engine starts to stutter, the engine is running too rich and you should jet down incrementally until the engine runs smoothly. A good sign that the main jet is correct is the colour of the spark plug.
Light brown = Ideal
Dark to black colouration = mixture is too rich (main jet is too big)
Grey to almost white = mixture is too lean (main jet is too small) and there is a danger of seizure or other engine damage.
