Got O.S 55sx for 3D flying. I used 13x4 APC props. The problem is, at full throttle the engine seems to quit, rpm slows down. However, at half throttle the engine seems normal. Tried tunning it thru air/fuel mixture but still the same. It was installed with a pitt muffler.

Please HELP

Run it full throttle on the ground and see if it does the same.If it isn't leaning out,it could be not getting enough fuel at full throttle,indicating a fuel pickup problem.Running it on the ground you will be able to see the fuel flow in the fuel line,or lack of.

Try it with the stock muffler. If it runs okay then you're probably getting too much backpressure from the Pitts or it doesn't provide enough muffler-pressure through the pressure nipple. In fact, check that the pressure nipple isn't blocked or partly obscured -- it happens.

Generally on most of the Pitts style mufflers you need to kink the exits in a little to add some restriction for more pressure.. IF your needle valve is much over 2.5 turns out then you need more pressure or a carb insert. .

Rick

Originally, 50sx is fitted with that stock muff and runs normally. After that, this problem occurs prompting me to replace it with pitt muff and still the same. Anyway will try to inspect the nipple if in deed obstructed. However, Im just wondering why the both types of muff have the same result, its hard to believed that both nipple got obstructed or it's just a coincedence. Is there any possibility of the glow plug to be the culprit?

Thanks

Originally Posted by Rickster

Generally on most of the Pitts style mufflers you need to kink the exits in a little to add some restriction for more pressure.. IF your needle valve is much over 2.5 turns out then you need more pressure or a carb insert. .

Rick

Hi Rickster, what do you mean on a carb insert? Does this mean a separate device?

Hi Guys, i think this case is SOLVED. I remember a few days back ,before this prob, i tried to clean fuel valve assembly. Unknowingly i was not able to put them back properly, the fuel inlet and fuel valve passage should be aligned properly to let fuel pass w/o obstruction, in my case it was almost 90deg misaligned giving limited fuel during full throttle causing the rpm to slow down.
Fixed this by trying to align the inlet-fuel valve-fuel outlet in one direction supplying enough fuel during full throttle and so far its doing well.

Thanks for all the informations.