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Peculiar petrol engine idle

Canít figure it out....maybe someone can

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cymaz12/05/2019 06:26:54
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8530 forum posts
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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 blush)

J D 812/05/2019 08:01:53
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1197 forum posts
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Any leaking on a crankcase of a two stroke can lead to problems.

cymaz12/05/2019 08:08:27
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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 p12/05/2019 09:06:00
218 forum posts
3 photos

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 Marsh12/05/2019 11:23:43
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moni g45 carburettor adjustments 0002.jpgWhat 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.

equalization_012.jpg

cymaz12/05/2019 17:23:57
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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

baf0338f-2d52-4640-b275-78591407eb0d.jpeg

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

cymaz12/05/2019 17:59:10
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8530 forum posts
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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 Marsh12/05/2019 19:16:53
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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.

cymaz12/05/2019 21:28:10
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8530 forum posts
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Great ! Will do. And the newly made gasket, I will report back. Thanks

cymaz17/05/2019 06:25:23
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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.17/05/2019 10:29:32
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1267 forum posts
1265 photos

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

D.D.

onetenor17/05/2019 17:04:46
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1900 forum posts

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

cymaz17/05/2019 19:24:19
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8530 forum posts
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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.

cymaz18/05/2019 22:44:27
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8530 forum posts
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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 Watkins19/05/2019 08:59:51
3746 forum posts
179 photos

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 baker19/05/2019 09:39:09
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1338 forum posts
291 photos

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

cymaz19/05/2019 10:30:05
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8530 forum posts
1150 photos

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?

cymaz19/05/2019 18:57:23
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8530 forum posts
1150 photos

Caught the problem on video today....

HERE

Tony Richardson19/05/2019 21:20:16
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601 forum posts
25 photos

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.

cymaz19/05/2019 21:35:38
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8530 forum posts
1150 photos

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 gasketssarcastic 2

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

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