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ASP 61 Four Stroke

Strange happenings

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Clive Moore26/06/2008 00:37:00
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150 forum posts
28 photos

Hi all,

I have been running an ASP 61 4 stroke (series 3) for about a season. Its had about a gallon+ of fuel through it. I ran it in as per instructions on the recommended fuel (and still fly on this, MT Irvine sport 5%)

Issues are,

1) It runs with the needle valve set at 11/4 turns open, open it much more (a couple of clicks) and it stops due to being over rich.  This was not always the case, it used to run on 2 to 21/2 turns open.

2) When running at full throttle the engine has started to emit an occasional loud crack sound which is only momentary.

3) After all the flying the engine has done I have not had one dead stick until yesterday when it stopped with three quarters of a tank of fuel whilst in straight and level flight at just over half throttle.

4) I've checked for air leaks in the entire fuel system and there are none (including inside the tank)

My questions are, Why has it changed to run on such a lean setting? (even the instructions say two to two and a half turns on the needle) and whats causing the noise? and should I worry about it?

Any ideas 

YakMad26/06/2008 09:19:00
517 forum posts
1 1/2 turns is usually the optimum setting for these engines, I have had and still have many ASP.61 FS which have been reliable once run in but can suffer from the O ring in the main neddle and idle needle failing, you should not have had to run it at 2 to 2 1/2 turns open this would point to the idle needle O ring leaking air. The simple solution is to order the main and idle needle from Just Engines which should solve your problem. The loud crack is probably pre-ignition as now the engine is running very hot as there is air leaking into the the mixture.
Ultymate26/06/2008 09:53:00
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1690 forum posts
57 photos
Clive it sounds to me like it may be time to reset the valve clearances (tappets) the cracking noise you're hearing could be a backfire in the exhaust due to the valve clearances being tight when hot giving  a leaky valve(s) and poor compression. The clearances are usually quoted in your manual in thousandths of an inch or fractions of a mm and are usually adjusted when the motor is cold.
Clive Moore26/06/2008 17:03:00
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150 forum posts
28 photos

Thanks guys. I've done the valve clearances, one was spot on the other was a mile out so have adjusted that back down.

 I think it is proberbly worth changing the needles so I'll get a set from just engines.

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