Diesel Tips

Mel Lyne with his nylon covered Super twister.

Mel Lyne and Remy Dawson.

Diesel Operating Tips for .15 - 19 cu in. engines.

by Mel Lyne

Some Basics:
1. Typically a new diesel will be quite tight, and will need 30 mins or more running rich and under compressed on the test stand before putting in a model. Use a 9x6 or 9x4 for easier starting when new.

2. Diesel fuel contains ether (a strong solvent), and will dissolve most rubber fuel pipe and bottles. Use clear poly type squeeze bottles and pipe or Sullivan Gasoline Bulb #171. Diesel attacks silicone (swells it up) Use P.A.W. fuel tubing, Aerotrend Aqua Blue Diesel fuel Tubing or Prather Gas Line.

3. A good fuel mix is 30% ether, 25% castor oil, 42% kerosene, 3% amyl nitrate. Once the fuel has been in a plastic fuel bottle, it loses some ether. For this reason it's a good idea to put "old" fuel in a separate can at the end of a session. This way the "new" fuel always stays pure. The less ether in the fuel, the harder the starting. Never store Diesel Fuel in plastic containers. Diesels leave a smelly, oily residue. Discard wipe cloths and other "stinky" items frequently. Diesels run at 27:1 compression, so mount them solidly to minimize vibration. Fill up the tank, and put on a thick glove or finger shield. A piece of rubber hose works well.

Starting Procedure:

1. Choke the motor 2 times, set the needle at about 2 1/2 turns open. If the motor doesn't fire in 6-8 flicks, screw in the compression lever 1/8 turn. If it still doesn't fire, give it 1 more choke. Try not to flood the motor. If you do, it will "knock back" or hydraulic when you flick. Back off the compression 1/4 turn per flick until it no longer hydraulics and is starting to fire repeatedly. Slowly take the compression up between flicks until the motor fires and keeps running. Increase compression 1/4 turn to get a slightly smoother run, then lean it out slightly. The motor should pick up rpm and smooth out.

2. For the first few runs on a new motor, run it rich and slightly under compressed. Lean it out to max rpm for a few seconds, then rich it out again. Run it for 5 minutes, then let it cool. A very tight motor may take an hour on the bench like this. Once you feel the motor is loosened up a bit, mount it solidly in a model. The important thing is not to run it too lean, especially when it is quite new. Start the motor on a 8x6 and warm it up to maximum power,

then open the needle 1/8 turn and fly it. It will lean out in maneuvers, and may misfire a lot. Ditch it and try again with a little more compression until you get a smooth run with just the occasional misfire. If at any time in the air the motor starts to labour and sound "Hard", ditch it soon. This is the over compressed condition, and can bend rods or worse in new motors. The motor will be very hot. Start it with chokes or a port prime, and back off the compression until it sounds happy. Then adjust the needle until you have max power, and open it 1/8 turn.