Fuel Jetting Guide

Carburetor fuel jetting can be a confusing and frustrating issue. An incorrectly tuned engine will run very poor and it’s amazing how such a small difference is fuel jet size makes such an enormous difference to the engine running and performance.

All Cycle Pro Road engines are specified with 0.70mm jets as standard. All CPM15 carburetors are specified with 0.70mm jets and come with a 0.65mm, 0.60mm, 0.55mm and 0.50mm jets as extras so the operator can fine tune the engine running.

Engine size, fuel type, oil mixture, engine spec, exhaust type and many other things affect what the optimum fuel jet size is. Please see the guide below to help you get your engine running at its best.

1. Engine is hard to start, needs a lot of choke, dies when throttle is opened, no power

Solution: Fuel jet is too small, fit larger jet

2. Engine runs a bit slow, smokes a little, top speed is not what it should be and engine make a ‘flutter’ sound and full throttle

Solution: Fuel jet is too large, fit smaller jet

3. Engine runs very slow, smokes, engine will need reach full revs

Solution: Fuel jet is too large, fit smaller jet. Also check that the air filter is not blocked.

A Note About Oils

It is very important that correct 2-stroke oil is used and is mixed at the correct rate. Please ensure that the fuel mix used is as stated here:

2-Stroke oil must be rated at either TC, or JASO FB, FC or FD (FA oil cannot be used). Any oil that is not rated or does not meet these ratings cannot be used.

Fuel/Oil mixture is 4% (40mm of oil / 1 Litre of fuel)

Failure to abide by this recommendation may result is very poor engine running, engine failure and also voids all engine warranty.