Petrol Newbie

[GrumpyGnome]

Good afternoon

I am just Dipping my toe in the world of petrol and have a couple of questions....

1. my glow powered models use three lines to the tank.... fill, carb, and pressure. My petrol engine does not provide exhaust pressure - do I leave a line 'open' to allow air to the tank to replace burnt fuel?

2. the engine runs nicely with power to the ignition supply only; when I switch on the radio, there seems to be a ton of interference, with all servos moving, including the throttle, and the motor stops. I assume this means there is a problem with my electronic ignition ? Can I replace it with any unit or are they bespoke? The motor is an RCGF 15cc..

Thanks in advance

Mark

[Shaun Walsh]

No expert on petrol engines in model aircraft but it might be useful to know what type of radio equipment (2.4 GHz or 35 MHz) and the make/type of the ignition system, is it CDI etc?

[john stones 1 - Moderator]

Put a photo of installation on, could be anything, might be ignition unit too close and causing interference.

[Bob Cotsford]

Check that the HT lead is well connected to the plug cap and that the plug cap is on the plug securely. When I ran petrol models I only had problems when the plug cap was loose or the HT lead faulty.

[GrumpyGnome]

Piccies later.

Layout as follows, from nose:

RCGF15cc rear induction side exhaust engine on standoffs

Fuel tank and tacho

Electronic ignition unit

Throttle servo - metal pushrod to carb, running alongside ignition unit

Switches (RC & ignition)

Satellite receiver

Batteries - RC and ignition

Spektrum AR6200 Rx (2.4)

Rudder and ele servos in tail, on extension leads.

HT lead to cap seems good. Cap to plug seems good. Have found plus a little loose ........... probably won't help!

Cheers, Mark

[Engine Doctor]

Are your Radio and ignition batteries together . if so serparate and try to keep ALL ignition wiring separate from radio with exception of lead to Rx from ignition cut off , Rexcel or similar.

Make sure you have plug cap securely fitted to plug . It may feel like its secure but a gentle tap down may sit it properly onto the plug . They can feel like they are attached but sit just off the plug and cause a spark to jump that will cause radio interference . re earthing the ignition . The plug lead should earth the engine to the unit . Their should be a light coiled spring tha fits into the bottom of the plug cap and presses on the cyl head around the plug area.

Servo leads especially long leads can act as an aeriels for interference so try to run then away from ignition circuit or fit ferrite rings to them.

I had a similar problem with my first ever petrol job that turned out to be a faulty ignition module .

Hobby king sell a replacement module costs around £28 - £30 its a good replacement unit have used a couple .

Edited By Engine Doctor on 27/08/2019 12:33:09

[Gary Manuel]

Mark,

1. Yes - leave the vent line open, but create a loop in the vent pipe that extends to the REAR and the TOP of the the tank to prevent syphoning when diving

2. Best advice I can offer is to keep ALL ignition wiring and components as far away from ALL receiver / servo equipment as possible. Run wiring for receiver down one side and to rear of fuselage and ignition down the other / front. Any wiring from either system that runs in close proximity can create interference problems. This includes battery and switch wiring.

It's also worth experimenting with fitting a ferrite ring onto strategic points in your receiver wiring if separation doesn't fully cure the problem.

Worth repeating that all HT leads connections, especially the plug cap need to be well connected as the spark created by a tiny gap in an HT lead is a very strong source of interference.

[GrumpyGnome]

Gosh, cannot believe this topic is so old! An update.......

 

Could never get rid of the interference so put it 'on the shelf' for a while.  In the meantime, I made the jump from Spektrum to FrSky for various reasons. Put an X8RPro rx in it - the recommended rx for petrol engines. Went off to the field to run it in. Could I get it to start? Could I heck!

 

In the meantime, I acquired a very low use Saito 82 - looked like it had never been run tbh. Bunged this in the Ultrastick and put the petrol back in the box for another project.

 

Eventually, the voice in my head forced me to take it out of the box. So I did and bunged it in an old Black Horse Yak 54 designed to 10cc 2-stroke.

 

Back to the field. Would it start? No. So, I checked ignition with one of those little gizmos. Fine. Checked that the plug sparked. Fine. Cleaned the filters. Checked the carb diaphragm and needs, fine. Got rid of all the old fuel. Tried again. Nope. Changed the plug. Bingo! Lovely petrol power with no interference, and a rock-solid radio link.

 

Not perfect of course as I have a few things to : 

 

a) move the throttle servo as it makes screwing the wing retaining screws in difficult

b) move the ignition unit as it's temporarily located on the engine box and prevents the cowl being used

c) put the cowl on once it's run in and final settings achieved

d) replumb the tank as, rather stupidly, I set it up as I would for glow.

 

It's been an interesting voyage of discovery. Thanks for all the help and suggestions.

 

GG

 

[Denis Watkins]

Just a quick note for storage from now on GG.

Store the model/ motor with the carb " wet ", with some fuel in.

Unlike glow, where we run the carb/motor dry,

With petrol, the diaphragm can dry out.

[GrumpyGnome]

Cheers Denis - will do.