Inverted Engine Problem

[Cenk Tugcetin]

Hi,
I have just completed building my new model, Ultimate 40S from World Models. This one requires installing the engine inverted.
I used my reliable OS 46 LA, which ran perfectly well on a previous model (sitting up right though). The problem I have is that the engine will not start at all inverted. I start the engine by turning the model upside down. This way, it will start OK but as soon as I turn the model over (i.e. when the engine is inverted), the engine will stop.
I can keep it running by keeping a very high idle but I believe it is not a good solution. BTW, I checked the tubing and I have the correct connections with the tank. I also replaced the glow plug with a new one (A3) but it did not help.
Many thanks in advance for your help.

[Allan Jordan]

Hi. Cenk, If your engine runs OK when upright I would suggest you check the clunk
in the tank,it sounds as if the problem is
fuel starvation. Is the clunk tube going
hard? Hope this helps. Regards Allan J..TTFN

[Danny Fenton]

Hi Cenk,
An inverted engine can be difficult to start if the prime is even slightly over-exuberant as the fuel will quench the plug. I often had to start a Tiger Moth I had years ago inverted, then once running flip it over. It did however idle fine either way up. Is the centreline of the tank in line with the carb? Perhaps a hotter plug might help with the idle??

[Cenk Tugcetin]

Hi Allan,
Many thanks for your advice. I checked the clunk, it seems to be moving freely.

Regards,
Cenk.

[Cenk Tugcetin]

Hi Danny,
Many thanks. I will check the centerline of the tank. I installed the tank as shown in the building instructions but you never know. I will also try a hotter plug.

Regards,
Cenk.

[Myron Beaumont]

Dear Cenk
Have always had problems with upside down motors & avoid the arrangement like the plague .Obviously in many many cases its the only way to make a model look like the real thing (scale) but the real things i.e .Chipmunks had an engine designed to run inverted (Cirrus) please correct me if i'm wrong . Do you build for flying & no fuss or build scale ? Like I said life is so much simpler if you keep it upright !With exhaust pressure the tank position i've found is not that critical to within a couple of centimeters or so Just like the CG with or without a full tank but thats another subject of controversity.Have just though of some thing -& i'm not inslting your intelligence but are you sure that your exhaust/tank system has the necessary gap in the tank to pressurise the tank?Cos really o0nce the motor is running then any change of orientation should not make any significant difference >inother words it's not the motors fault Advice --If possible mount it on it's side Thats what I do then you know it will behave it's self no matter how you fly !Let me know how you get on .

[the unmagnificent man]

Hi Cenk, having read the previous threads I have to agree with Allan and Danny and say that the clunk is the most likely candidate. Although you said it was moving freely have you checked that when you turn it over that it is actually dropping from the bottom of the tank to the top and not just hitting the rear of the tank and stopping. This would still sound like it is loose but would not fall into the fuel. This method only applies if you do not have a full tank of fuel however. Another thing to listen for is when you start the engine normally and then turn it over does it splutter to a stop (too rich) or does it seam to speed up just before it stops? a sure sign that it is fuel starvation upside down. Also what Danny said about the tank level compared to the carb could also be a contributing factor. Good luck. Al

[nasa_steve]

cenk
i've had exactly the same problem with the same engine i reverted to starting it the right way up then flipping it over and as the other guys have said it is down to clunk position and the tendancy to have the clunk in inverted set-up models higher than the carb thus flooding the engine
regards
steve

[Cenk Tugcetin]

Hi,
Many thanks to all of you for your invaluable advice.
I removed the tank yesterday, shortened the clank tube a bit to guarantee free movement. I noticed the pressure pipe was almost touching the top of the tank so re-adjusted the angle to allow some more room.

To answer Al's question, the engine is spluttering to a stop so I beleive it is more of a flooding problem rather than starvation (may be what I did so far will not improve the situation).

I will give it another go this afternoon and let you know how it went. If it still refuses to run, I will probably have to go down to the model shop and grab a hotter plug.

Regards,
Cenk.

[geoff dales]

ive had the same model myself and had a 52 fs in it theres a couple more of these models where i fly also both fitted with 4 strokes. i try and avoid inverted 2 strokes wherever possible because as your finding they can be troublesome

[Cenk Tugcetin]

Hi,
I tried to run the engine inverted on Friday again, following all the advice I received in this thread (I did not try a hotter plug though as I could not get one easily). No luck. So, I refitted the engine horizontally. Although this meant some unused holes in the cowling and late hours into the Friday evening, the engine now runs perfectly. I had four good flights in Saturday's fantastic weather and I am very pleased with my new model now. I managed to cover the original holes in the cowling with Solarfilm and some of the decals provided with the model.

So, lessons learnt:

1. Try to avoid fitting the engine inverted (well, I don't have any experience with the 4 strokes but this is true at least for the 2 strokes).

2. Do not fit the cowling until you make sure the engine is running OK in its intended position. This would have saved me many building hours and I would end up with a much better looking cowl.

Many many thanks again for all your help.

[Colin Hostler]

Next time you fit an la inverted put "Type F" plug in, worked for me.

[flytilbroke]

This same question was asked recently perhaps on another forum, I also suggested a Four stroke plug "F" as that cured one of my inverted engine problems

[Aero120]

I had exactly this problem with My Hangar nine mustang. The problem was not the plug, or the fuel but the bottom end mixture. I had to start mine with the engine the right way up and like yours it wouldn't idle at all with the plane the right way up.  I leaned the bottom end off by over a turn and now it will idle for over two minutes and pick straight up. My engine is an OS 91FX and initially ran fine but as it ran in the needle settings seemed to go their own ways. The top end went lean and the bottom went rich. However its sorted now. If your engine runs fine at full throttle then the plug isn't too cold, if the revs bog down at idle but pick up when you reconnect the glow, the plug is drowning. If there's plenty of oil coming out of the exhaust as it idles then its a too rich mixture drowning the plug rather than the plug coolling too much on its own.

[Gary Vinten]

Hi

I agree with the last post , you need to set the slow running jet may be one turn but bdo it small amounts at a time untill the engine runs at low revs, then adjust the needle valve for your top end , this will give you a perfect running inverted engine. But remember when you put it in a normal position it will have to be re callabrated again. I run 3no engines inverted and all set up this way and all run fine.

Good luck