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There are several sites out there that tell you how to modify a Ryobi 31cc
engine for flight use. Refer to these to fill in the gaps in my explanation as I will
be covering some of the more confusing aspects.
Despite what you might be thinking now, it is very easy to do with a few
basic tools. The first step though is get yourself a gas powered weed eater to
modify. Used ones can be picked up for next to nothing at your local small
engine repair shop but will probably require some TLC to get running well.
Once you have a motor, dig in and start removing the shaft and any plastic
parts that are easily removable. Your engine should look like this when it starts
to get interesting. The next step is to remove the bell housing from the front of
the motor assembly. Easiest way if you don't have a small screwdriver is to cut
the end of the housing off with a hacksaw. This will expose the screw the holds
the housing in place. Keep the engine from rotating when removing this screw.
Remove the housing and the clutch pieces underneath. This will leave a large
nut behind that simply is unscrewed. Keep the nut just in case. Also, carefully
remove and keep the fuel bulb from the back. This comes in handy for priming
the motor when you get ready to start it. I have found that making the primer
bulb part of the fuel system makes for an engine that likes to run inverted.
Next remove the rest of the plastic cover which leaves only the fuel tank
and the backplate of the engine that the carburetor mounts to. The motor looks
like this and this. Remove the carburetor and then the four screws that hold the
backplate in place. Slowly remove the backplate so that you don't tear the
gasket.
Slowly remove the gasket from the backplate so that the backplate can be
cut to size. You want to trim the piece along the ridge that runs around the
fastener pattern. While the backplate is off, take the time to modify the reed
valve retainer's gap. This will allow more fuel into the engine for more power.
Bend the reed valve retainer until an 1/8inch allen key can just slide between
the retainer and the reed valve.
engine for flight use. Refer to these to fill in the gaps in my explanation as I will
be covering some of the more confusing aspects.
Despite what you might be thinking now, it is very easy to do with a few
basic tools. The first step though is get yourself a gas powered weed eater to
modify. Used ones can be picked up for next to nothing at your local small
engine repair shop but will probably require some TLC to get running well.
Once you have a motor, dig in and start removing the shaft and any plastic
parts that are easily removable. Your engine should look like this when it starts
to get interesting. The next step is to remove the bell housing from the front of
the motor assembly. Easiest way if you don't have a small screwdriver is to cut
the end of the housing off with a hacksaw. This will expose the screw the holds
the housing in place. Keep the engine from rotating when removing this screw.
Remove the housing and the clutch pieces underneath. This will leave a large
nut behind that simply is unscrewed. Keep the nut just in case. Also, carefully
remove and keep the fuel bulb from the back. This comes in handy for priming
the motor when you get ready to start it. I have found that making the primer
bulb part of the fuel system makes for an engine that likes to run inverted.
Next remove the rest of the plastic cover which leaves only the fuel tank
and the backplate of the engine that the carburetor mounts to. The motor looks
like this and this. Remove the carburetor and then the four screws that hold the
backplate in place. Slowly remove the backplate so that you don't tear the
gasket.
Slowly remove the gasket from the backplate so that the backplate can be
cut to size. You want to trim the piece along the ridge that runs around the
fastener pattern. While the backplate is off, take the time to modify the reed
valve retainer's gap. This will allow more fuel into the engine for more power.
Bend the reed valve retainer until an 1/8inch allen key can just slide between
the retainer and the reed valve.
