Hovertechnics Hovercraft - Hovercraft Maintenance

Single Fan Hovercraft Maintenance

Hovercraft Safety and Maintenance Must Do's and Dont's

The hovercraft maintenance procedures on our web page are an introductory guide and not a complete set of maintenance instructions. It is important to read the Maintenance section in the Operator's manual which is more detailed and is specific to each hovercraft model.

For Maintenance and Operator's manual prices please see the Training section.

Principles of 2-Cycle Engine Jetting

The jets in the carburetor serve to control the amount of gasoline going into the cylinders. Jets come with different hole sizes which are indicated by numbers stamped on the jet. The larger the hole in the jet, the higher the number (e.g. 152.5 is larger than 150 and allows more gas into the cylinder). Jets can be changed easily by undoing the float bowl. Consult the engine manufacturer's handbook for more details.

The amount of gasoline entering the cylinder has an important affect on cooling the piston. The essence of good engine performance is to have the correct air to gasoline ratio. Having the wrong ratio can produce the following effects.

TOO MUCH GASOLINE (JET TOO LARGE)
(rich mixture)

Engine hesitation during acceleration;

Engine will not reach normal maximum r.p.m.;

Spark plugs are black and/or wet.

TOO MUCH AIR (JET TOO SMALL OR AIR LEAKS INTO FUEL SYSTEM OR CYLINDERS)
(lean mixture)

Spark plugs are white or gray in color;

Overheating causing burnt piston with loss of power;

Engine seize-up

The affect of ambient temperature and altitude on the fuel/air mixture is important. As the ambient temperature or altitude increases, the oxygen content of a cubic meter of air gets less and it is necessary to reduce the fuel amount correspondingly by using a smaller jet.

As the ambient temperature goes down or you move the craft to a lower altitude, it is necessary to change to a larger jet to avoid burning pistons.

When making jet changes it is advisable to reduce or increase the jet size one step at a time. A step is 2.5 or 5 whole numbers (e.g. 155 to 152.5 or 260 to 270). Test after each change by examining spark plug color immediately upon switching off engine after a five minute run. Check for hesitation during acceleration. A little hesitation is safer than none at all.

If you have dual carburetors it is sometimes usual to have one size larger jet in the rear carburetor than in the front one. This is because the rear cylinder usually runs hotter than the front one since the cooling air is already warm when it passes the rear cylinder.

Air leaks can also cause lean mixture and can come from faulty valve, cylinder or exhaust gaskets or air entering fuel lines at connections.

A dirty air filter can also cause rich mixture by reducing air volume.

With climate changes or major altitude changes it is necessary to change jet sizes until the correct chocolate brown spark plug color is achieved.

Jetting charts for engines are available upon request.