I hope someone can shed some light on this for me im running a MacC 28cc weedwakeer engine with a airtronics radio gear nothing fancy ...the question is Im still getting what I believe to be e.m.i. interferance to my servos ...Ive grounded the engine to the landing gear wich is a good chunk of metal and the batterie pack is about 18 inches away from the motor ...reciever is about the same but im still getting a little glich wile field running ....is there somthing else I could do to help eliminate this glich??........planeless in Chamainus

You are running a resistor type spark plug, right?

Look at all your linkages to make sure there is no metal on metal anywhere.

steamer401 ,

You don't want any metal, such as push rods,servo and battery leads between the engine and radio. The plug has to be a resistor type. Plug gap 0.020 to 0.025. Usually has an "R" in the model number. The plug cap has to be tight. Don't ground the engine to the gear, it may act as an antenna for RF.

Dave

AAHHH !!!I am not running a resister plug ....and its not a good idea to ground to landing frame of aircraft ??

no.. that is not a normal practice

R plug is needed for sure!

One should never provide an additional ground conductor path... One ground wire/cable from the ignition module to the engine ONLY.... Typically plug cables provide the connection between the engine block and spark module.

Typically the ground braid is attached to the base of the sparkplug (sometimes with a hose clamp). The other end is attached to the aluminum case (internally). This is the (only) correct configuration.

No extra ground leads should be attached from the (aluminum) ignition box to the engine.

One can ground at the sparkplug base (best), or from the aluminum casing to the engine block. You can have one, or the other, but not both.

The best is the shortest distance to GND, which would be the braid attached to the metallic plug base or right nearby. A shorter length of braid is resonant at higher frequencies. Making the braid as short as possible has merit (just enough slack to act as a strain relief against engine pulses) and crimp a HD eyelet on. I then drill the nearest cylinder fin (close to the main cylinder head mass) and bolt it on using Loctite. (This eliminates the hose clamp provided with some ignitions and associated problems)

Never solder the eyelets to the braid, as this has just defeated the strain relief right where it is needed most (right at the junction where the braid enters the crimp area).

thanks mglavin I will read through your reply a few more times to fully understand your explanation....and i have purchased a "R" plug from a local small engine place in Victoria and have tested it tonight in the back yard and i did about 10 laps and not a glich ...looks good so far ....the other question is what would be a good starting point for a prop for this engine the 18.5 I have seemes to bog the engine down ...maybe ile try a 16.5 or somthing ...what about rapping the spark plug wire with aluminum foil just an Idea?

A 28cc Mac likes a 16x8 for a go fast, and an 18/6 or 18x8 for a floater. With a basic stock engine prop for 7000 rpm