Navy_Guns

I have a Hangar 9 Alpha 60 and have installed the supplied 3-blade prop on my Fox Eagle .74 engine. I have not flown it yet because I have a concern when ground testing the engine. When I open the throttle to about 3/4, it sounds great and has plenty of power. It idles fine and everybody's happy. When I open the throttle all the way up, the revs start to die off almost like it's too lean, but even after backing out the high speed needle A LOT, it is still behaving like this. The usual "is it too lean" test I'm familiar with is to run it to full throttle and point the engine up and see if it starts to die, but this does it no matter what the attitude and just doesn't sound like a "too lean" scenario. I'm starting to suspect that the really flat pitch of the prop (I think it's a 12x4) may be ok for a .61 engine but is too flat for my .74. Does this sound plausible, or is there something else I should look into?

carrellh

From the Fox site, the engine should turn around 12,700 rpm with a 11x8 two blade. Do you know what it turns with the evolution prop? I've read that the trainer props are very low pitch so it may not be enough for the engine.

dant-RCU

My Feedback: (3)

I have run numerious Fox .74 engines and always used a 13x6 two blace (per Charlie's advice a number of years ago) and also had very good
luck running a 12x6 three blade. I suspect that your "flatter" pitch is not helping you. From MY PERSONAL EXPERIENCE, if you want to run a
three blade then go up to the 12x6.

Dan

jester_s1

The prop shouldn't cause the kind of trouble you're having. A 2 stroke engine can turn a lot of RPM's with light loading. Given that the needle valves can be opened up enough to make the engine blow raw fuel out of the exhaust at full throttle, there's no way you're turning so many RPM that the needle valve can't supply the engine with enough fuel. I'd suspect one of two things based on what you're describing. The first is an air leak, either in the fuel line or in the engine at the carb inlet or the front bearing. The second is an obstruction in the spray bar (the passages are really small so it doesn't take much). For the former, watch for bubbles in your line going up to the carb to check the line, and put a new o ring on the carb. For the latter, unscrew the needle valve and gently push a piece of wire into the spraybar to clear anything out that's in there.