geofferama

this is probably be a stupid question, but how come gas engines (like my weed wacker & chain saw) don't need any kind of spark or heater to get them going?

One of these days i'll rip apart a broken weed wacker and take a look, but can anyone give me the short and simple version in the meantime?

CowboyBob

They do require a spark or ignition to get them going (just like any internal combustion engine). In my limited experience with 1/6 scales and small engines, the Zenoah engine has an ignition module that is located behind the flywheel/engine cover. The ignition module is triggered by the flywheel (I think) as the pull starter is yanked...thus creating the spark to allow the engine to start. Of course, once the engine is running the ignition is continually triggered/activated by the flywheel (or maybe the crank...I'm not sure).

JRexA

The Zenoah has a Magnetic Ignition. just like the Moped I used to ride some 25 years back. It is the same way that Ignition is generated on a Piston driven aircraft, except that piston powerd aircraft have dual Magnets and Dual Sparkplugs.

The big advantage of a Magnetic Ignition is that you don't need a seperate power source/battery for the Ignition.

On my old moped, I had to adjust timing by moving the ignition coil.

Best from Greenland
Land of Santa
Jesper Rex

p.s. IMO: The only stupid question is the one you know that you forgot to ask before going out and doing something the wrong way.

pehter aka ibbe

http://science.howstuffworks.com/two-stroke.htm
Basic about two stroke engines

http://home.howstuffworks.com/chainsaw5.htm
How the spark generates.

ZondaC12

with nitro engines u need a "heater" to start them because that heats the glow plug coil up red-orange hot and that will ignite the nitro fuel, then as the engine is running, the heat from the compression and the fact that the engine actually keeps the plug's platinum coil hot keeps the fuel igniting.

geofferama

hey all
thanks for the responses, the how-stuff works article helped me visualize JRexA's answer.

Does the magneto setup add to the rotating mass? Cause I imagine it robs the engine of a slight bit of horsepower

ibstar

no adding to roatating mass
theres just a small magnet in it which creates the pulse as it passes the coil.
the flywheels there to aid cooling anyway