I was out yesterday flying my Enya SS35 - powered Chizler  ( . ).   What I had was a nice 4-cycle in upright flight and inside manoeuvres, but a break into a 2-stroke when inverted or during outsides.   Now this is great for vertical eights and during the 3rd loop of the clover, but obviously not ideal overall (though I was still having plenty of fun with it).  

My first thought was that the tank obviously needed to be lowered a bit - but if that is the case, wouldn't the thing also have been breaking into a 2-stroke when climbing vertically, due to the much lower fuel head? (It wasn't.)  Might it instead be something happening with the fuel/air mix inside the crankcase?  

Would muffler pressure be likely to help?  Or should I just stop mucking round with 4/2 breaks and run the thing in a wet 2, which is how I expected to be running it in the first place?

Cheers
Steve

How is your tank vented, standard or uniflow?

With uniflow, you should be able to fix your problem by moving the tank.

I'll try that then - but I'm still a bit mystified why it doesn't break into a 2-stroke when pitched into a vertical climb, considering the position of the fuel relative to the engine.

   Because the breaks don't have much to do with the fuel pressure (or the mixture, for that matter).

    Brett

Which would mean that the tank height isn't the issue here, Brett?

(Edit - just read your comments on the 'Wet 2' thread.)

I "might be wrong" (it does happen once every millennium or so), but I don't think that's what I read from Brett's post.

I think a change to the tank height is needed.  The "break" will be determined by other factors, like "load".

And I am sure Brett will correct me if I am wrong!

Big bear

Has anybody tested  to see if muffler pressure significantly increases fuel temp? Since there's no real flow of hot exhaust through the tank, I can't see it being a big increase. A minute flow into the tank is all that happens...same amount as the fuel volume what's leaving via the NV. Probably a bunch less temp increase than would be caused by a header or muffler installed in the same compartment, I bet. In fact, I'd be so bold as to bet a dollah that it's less.   Steve

Has anybody tested  to see if muffler pressure significantly increases fuel temp? Since there's no real flow of hot exhaust through the tank, I can't see it being a big increase. A minute flow into the tank is all that happens...same amount as the fuel volume what's leaving via the NV. Probably a bunch less temp increase than would be caused by a header or muffler installed in the same compartment, I bet. In fact, I'd be so bold as to bet a dollah that it's less.   Steve

Hi Steve

Yes it does raise the temp inside the fuel tank, You can put a running engine setup on a bench with a clear plastic tank and see how much hot gas goes back into the tank. I had this setup and when you look at the fuel on suction it is clear and you can see the fuel level,,hook up the muffler pressure line and the tank will immediately go into a seething mass of white foam, you cannot tell the fuel level and all you can see is bubbles everywhere into the tank. I was surprised on how much flow goes into the tank from a tongue mufflers, Even more from a tube muffler...and a pipe puts even more flow back into the fuel tank. I will also unfortunately put debris back into the tank from things like dirt ,sand, bugs, grass or whatever gets into the intake of the motor, and some times burned hard carbon bits from the exhaust system,as well as burned hot oil.

Randy