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engine getting no fuel

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stuart macrory31/12/2007 17:27:00
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110 forum posts
hello all,hope someone can help me.i have a blackhorse super with an os 46la engine in it,problem is everttime i start doing acrobatics with it the engine cuts.(most of the time 3-5 mins in to flight)this means i have to land dead stick everytime and as i am pretty much a beginner this is making me more and more nervous of flying.this have happened about 6 times now and everytime on closer inspection of the plane i can see that the fuel line is empty??i am pretty sure that the tank is plumbed correctly(1 line for the clunck which is moving freely inside the tank and 1 breather tube which is attached to the muffler)anybody any ideas????
Tim Mackey31/12/2007 18:04:00
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Are you SURE the clunk is not touching the tank bottom when inverted /rolling whatever. Also, ensure that there is enough fuel actually loaded to be able to do manouveres after 5 mins of flight, maybe the level is very low by then? - have you tried these as soon as you have taken off and reached a safe height?
stuart macrory31/12/2007 18:14:00
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110 forum posts
thanks for reply,i took the tank out of the plane and the clunk does touch the tank by a fraction but the hole in it is clear of the bottom(its only the edge of the clunk touching),the fuel level is probably about at about 1/2 when this usually happens.would it be an idea the put 2 clunks in the tank with a y connector?
winchweight31/12/2007 18:21:00
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Running a bit too lean perhaps?
Tim Mackey31/12/2007 18:25:00
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NO, forget 2 clunks....the system should work with 1.

There are several potential reasons, including Shauns suggestion of being too lean. I take it you always do the "nose up" high throttle test before flight?

I always ensure my clunk line is short of the tank bottom by around at least .25 Inch, and insert a piece of rigid tube in it also to stop it folding over.

stuart macrory31/12/2007 18:55:00
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110 forum posts

yes i do do the nose up test before flight and its ok i think ill try shortening the tube on the clunk a fraction and see if that makes a difference.

timbo, with the rigid tube up the line does that not cause you problems when the fuel is down a bit when flying inverted?or is the rigid tube quite short and still allows the clunk the move freely?

Eric Bray31/12/2007 20:48:00
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From that, I'd say that you have put the tank into the fuz incorrectly. The neck of the tank should face the engine, so that the clunk weight can draw fuel whichever way up the model is. It sounds as though you have put the tank in with the neck facing up, when the model is on its wheels. As a result, the clunk weight cannot fall to where the fuel is, as it needs to bend the fuel line into a u shape inside the tank!

I may be wrong in my reading of your comment. 

If you put two clunks into a tank, on a 'y' connector, should one get stuck, it will allow the engine to suck air, and not fuel, because air is lighter than fuel. 

Tim Mackey01/01/2008 16:13:00
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It is only a short length of tube, still allowing full flexibility of the tube to "scavenge" around the tank as required, but long enough to prevent it folding over itself.
stuart macrory01/01/2008 18:45:00
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110 forum posts
going on what shaun says,as a beginner how do i know if the engine is to lean(its sounds to be ok and its putting out a good bit of oil on to the wing after each flight)
Tim Mackey01/01/2008 19:08:00
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If it starts to labour / slow down when nose up, it may be too lean. Lean running means overheating, and its always wise ( IMO ) to find the highest RPM by turning IN the needle valve, listening carefully for the engine slowing off slightly as you pass this crucial point, and then back off the valve to get it ever so slightly rich.
Paul Adams18/07/2008 16:09:00
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How flexible is the tube inside the fuel tank?  Have had experiance in the past where coming out of a spin (nose down) the engine has cut. On investigation I found that when the model was nose down the cluck tube kept the clunk at the back of the tank. I changed to a very flexible tube and it curred the problem.  

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