Peculiar petrol engine idle

[cymaz]

i have an RCGF 30cc petrol engine. The engine is inverted. Starts well, idles well.....until you put the nose down whilst holding it. It slows and dies! However, invert the plane ( so the engine is upright) and do a nose down it’s a smooth steady idle.

The plug is tan brown and shows no oily residue. The mix is 32:1 with fresh fuel and good quality Castrol oil. There are no carb leaks, metering needle is set correctly. There is a small leak in the crankcase around the casing halves. It’s a 3 line plumbed tank.

Its got me ! Anyone know the cause ( apart from the usual joke , the wrong letters are on the crankcase )

[J D 8]

Any leaking on a crankcase of a two stroke can lead to problems.

[cymaz]

That’s what’s puzzling me. Up right it will run strong and steady in any position. If it was stopping upright or playing up then I would reseal all the mating surfaces. As it’s only in one tiny spot.

I’m afraid I might introduce more leaks reassembling it. I’ve got some high temp gasket sealer when I took it apart 6-8 months ago...it been reliable up to now.

[alan p]

Leaks in the fuel supply chain, has the tubing developed pin hole leak in the tank , tipping nose down could be exposing it to pulling in air?

[Paul Marsh]

What aircraft is it in. I have a RCGF 30cc in a Yak 54 and had to modify the carb to get it to run right - by adding a pressure equalization pipe.

[cymaz]

I’ve got one on Paul but it doesn’t go all the way into the fus. The engine is being run in the fuselage in the back garden at the n moment. It still shows almost the signs of fuel starvation or the plug getting swamped with fuel, can’t make up my mind! Very worrying.

i need it done soon, I hope to take it to Wings and Wheels

Edited By cymaz on 12/05/2019 17:34:26

[cymaz]

The two halves of the crank case have no gasket and I can’t seem to find one in the parts pictures. Therefore gasket paper ordered.

[Paul Marsh]

That was the symptoms i was getting, no fuel, then a full load swamping it and making it wet.

Cured by the above mods. Extend the pipe via fuel tube into the fuselage.

[cymaz]

Great ! Will do. And the newly made gasket, I will report back. Thanks

[cymaz]

Purchased a sheet of 0.4mm gasket paper. Cut out a gasket for the mating halves of the crankcase. The surfaces where quite fine like machined bit obviously not good enough for a tight seal as some fuel leaking was seen on engine run.

The diaphragm air bleed modification I did has now been extended into the fuselage.

Now all is needed is an engine run

[Dwain Dibley.]

Fingers crossed here, Cymaz.................

D.D.

[onetenor]

IDEALLY BOTH ENDS OF THE BALANCE PIPE EMERGE TOGETHER imho IN THE SAME SPACE This irons out the ripples hopefully..

[cymaz]

Came in from running the engine. No leaks anywhere on the crankcase or carb. Nose down there is no sudden cut. It will idle for at least a minute. It’s very sensitive on needle adjustments.

Will fly it at the field Saturday.

[cymaz]

Well it had a couple of runs. Fine tuned the needles and all was well......until........

it started to idle roughly, hard to start and poorly. After some research it seems the Hall effect sensor could be playing up. Changed the sensor, now waiting to run it up again.

[Denis Watkins]

You have climbed a mountain and back again Cymaz, with this one

The sensitive needle is usually an indicator of Plumbing ! ! !

So somewhere from the fuel to the cylinder

Is a leak or blockage

Is there any chance, on the bench, of running another supply in tandem, directly to your carb nipple

Removing your present fuel installation from the equation.

I have done this by banding on another tank and pipes on the fuz side bypassing the model installation entirely for the test

[bert baker]

It may be worth checking that all the battery leads are a good fit and do make a good contact across the connector rather than a tight plastic connection,,,,

and the battery is there a possibility one of the welded terminals has or is failing under vibration and loads,

I had similar problems and that was what cured mine

[cymaz]

Cheers Bert, will look into that. There’s not much that’s been checked and double checked. Now it’s a process of elimination all over again.

By the way, are you on for Wings and Wheels this year again?

[cymaz]

Caught the problem on video today....

HERE

[Tony Richardson]

Cymaz, are you sure its not the throttle servo, I had a mini digital - spektrum 5030 - on an NGH38 and the vibration caused it to keep trying to find neutral and it would "hunt" eventually stalling the engine, just a thought.

[cymaz]

I've changed the servo to a Hitec, that's what I thought the problem was originally.

Off to order a new carb rebuild set and carb gaskets

Edited By cymaz on 19/05/2019 21:36:46

[Tony Richardson]

Do you have a spare CDI unit you can try?

[cymaz]

I changed the CDI box about 9 months ago..... I will have a look but I doubt it.

[Tony Richardson]

Cymaz do you have a switch -opto coupled - that you can turn on/off from your transmitter, if so is it in conjunction with a manual switch? you may want to check all the wiring and connections, I have a clubmate who had similar issues and traced it to a failing opto switch, the switch was fine on startup bur after running for a while tended to heat up a little and made for erratic running. I"m clutching at straws here and am inclined to think it is a fuel feed problem but you have checked all that and it appears to be fine. When you find the answer - as you certainly will - please let us know what it was and the solution I hate unsolved mysteries..

[Martin McIntosh]

I have an RCG (not RCGF) 30 which is fine, also a similar RCG 50. The 50 started to quit after 2.5 mins in the air or on the ground. Someone spotted a tiny piece of black crap in the fuel line just by the carb. It could not be sucked out due to the diaphragm being closed but I got it out in the end. Could be a similar problem with yours. Hope you sort it before W&W.

[cymaz]

Carb rebuilt kit has arrived, the gasket set is in the post. I’ve also ordered all the fuel tube, bung, brass pipe and barbs to completely rebuild the fuel system.