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Petrol engines

Published: Wednesday, 08 June 2011 09:12 | Written by The Burglar |

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PETROL {GAS IF YOU ARE AMERICAN} ENGINES AND THEIR FOIBLES

BY THE BURGLAR

These days petrol engines are rapidly becoming more popular, particularly as our models get bigger

and more complex ,and for some very good reasons. They are more reliable than their glo cousins, but

they do have their little idiosyncrasies .The greatest difference lies in the carburettor set up. They have

an inbuilt petrol pump, so you can mount your tank anywhere in the plane, height above the carby

matters not a toss, and with the throttle closed you cannot flood the engine while refueling. Also

because of the fact that you have a spark plug and not a glo plug, the engine can be mounted inverted

with no fears of poor idling or poor running.

The one thing that can be a trap with petrol engines is the little balance port on the pump side of the

carby. If it is in a position that can be influenced by different air pressures, like facing into the airstream

or in a pressure void inside the cowl, erratic mixture settings will result during certain manoeuvres .The

insurance against this is to always when installing a petrol engine, solder a short length of brass fuel

tube over this tiny hole and run a length of fuel tube back into the fuselage,where you will not get

sudden pressure variations. If you are unsure of the location of this hole, ask me or one of the other

petrolheads in the club. Whilst on the subject of fuel tubing, remember that you MUST NOT use

silicon fuel tubing, you must use the TYGON fuel tubing, readily available from hobby stores or from

lawnmower or motor bike shops.Also it is a good idea to put a small cable tie around every junction of

tygon over brass tubing, because the tygon can stretch over time and slip off the end of the brass tube.

Very embarrassing !!Also the stopper in the neck of your tank must be of the gas type and not the glo

fuel type. Most tank brands will supply a gas stopper.

FUEL MIXES. Most makers these days like you to run the engine in on a higher ratio of oil to petrol

mix, usually 25 or 30 to one, using a MINERAL rather than a synthetic oil, so that the surfaces get

bedded in properly. Later when fully run in use a top quality Synthetic oil which you can get from a

Motor bike shop, one of the offroad racing synthetics is the go, and follow the makers advice as to

ratio, usually around 40 or 50 to one. These engines are very frugal as well, you will get about twice to

three times the run time as a glo engine on the same size tank. As you can see they are very cheap to

run.

MIXTURE ADJUSTMENTS. These engines are a bit different to glo in the way you set the high and

low mixture settings. Set the high first, and run it a bit rich for the first hour or so, and remember that

when setting the low speed needle, this usually affects the high setting as well, so if you richen up the

low needle chances are you will have to lean off the high a bit as well. Listen to the transition, if the

motor “dies”on opening the throttle chances are you will have to richen the low speed needle, if it

“hunts “and surges when you open the throttle chances are it is too rich on the low needle. Don’t forget

that as you change mixture settings on the low end your idle speed will vary, so always adjust this after

altering the low needle.

STARTING TECHNIQUE. If your engine is of the Magneto type like a Zenoah,don’t even think about

hand starting, the propeller has to do almost a complete turn before a spark is generated, so just flipping

it over compression is a no brainer. Either use a starter or have the motor fitted with a spring starter,

which spins it over several times quickly. Close the choke FULLY and open the throttle fully, spin the

engine and when enough fuel is pumped into the carby it will “pop” or just fire once. Then open the

choke, put the throttle just above idle, spin it and it will start. If your engine has electronic ignition and

no magneto, then it is possible to hand start because the spark is generated at top dead centre by the

ignition battery without the engine having to do a full turn. However for my money and because I

prefer my fingers to stay attached to my hand, I use a starter even on my electronic ignition engines. In

fact with the bigger engines,say around 80cc up, this becomes a case of prefering my whole arm to stay

attached to my body !!!!

ALWAYS have someone help you and hold the model, those bigger engines can develop a lot of thrust

and power, on full power my 3W80 will almost drag my helper {RON} along the ground with his

heels dug in !!!!

Good luck with your petrol engines !!!! If you need help just ask.

THE BURGLAR

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