The plane is a Topflight Nobler at 44 oz. and the engine is a Tom Muggleton OS 40FP. It flies great on 63 ft. lines. The prop is a 10 1/2 x 5 Bolly Clubman (not shown). The tank is a 4 oz. metal. The engine runs a real solid 4 stroke and has a soft break in the overheads. Fuel is Power Master 10% nitro, 18% oil at 50%/50% plus I added 8 oz. of Sig Castor.........Example: it does not break when the nose is lifted or pointed up. It doesn't break until it almost reaches the top of the wingover and then as soon as it heads down it goes back into a solid 4 stroke. There is always plenty of power.  "My question is can it be made to break sooner ?"

Yes, but why?? If there is always plenty of power, it's working!

Our PA 61s do exactly what you're describing.  It's not a problem........

is it??

Bill <><

Oh, ok! 

Man, you had me worried there for a minute!

Changing the needle setting, changing venturis, changing compression, changing props, changing nitro.  Any/all of these will affect the break.  Bigger venturi helps to break quicker is my understanding, along with more compression or more prop load.  Randy can be more specific! 

Bill <><

The plane is a Topflight Nobler at 44 oz. and the engine is a Tom Muggleton OS 40FP. It flies great on 63 ft. lines. The prop is a 10 1/2 x 5 Bolly Clubman (not shown). The tank is a 4 oz. metal with muffler pressure. The engine runs a real solid 4 stroke and has a soft break in the overheads. Fuel is Power Master 10% nitro, 18% oil at 50%/50% plus I added 8 oz. of Sig Castor.........Example: it does not break when the nose is lifted or pointed up. It doesn't break until it almost reaches the top of the wingover and then as soon as it heads down it goes back into a solid 4 stroke. There is always plenty of power.  "My question is can it be made to break sooner ?" 
                                                   

Hi Greg

Typically the easiest way to make a motor break faster is too drop the nitro percentage, you then have to turn the  needle leaner to get the power back, this pushed the motor much closer to a 2 cycle,  Natutally the opposite happpens most times, when you add nitro it increases power and you turn the needle out richer, many times this will result in an almost all 4 cycle run, or just a beep in the tops......however it is not at all simple..
Some motors are not happy with a 2 cycle throughout most of the manouvers, some like to 2 cycle a lot some will just beep 2 cycle at the tops of the manouvers. The classic 4-2  is for the motor to break into a 2 cycle at 9:00 and back to a 4 cycle at 3:00.
What you want to be concerned with is the type of run your  engine-plane combos likes, and what type of break, if any your motor works best at.
If your a PAMPA member you can look at the engine article I wrote last summer, it goes into much more detail  about this.
As always if I can help you with specifics  please let me know

Regards
Randy

 Move the tank back (if room permits) about 1/4th of an inch.

  Marvin Denny

Hi Randy,
Is the engine article you wrote last summer on the PAMPA website?  I'm a member and looked for it, but didn't find it.  I too would like to learn more about how changing the variables affects 2/4 break as well as other related things.

Thanks,
Kim Mortimore

HI Kim

I am not sure if it is or not, I will try to find out , in the mean time if you cannot find your copy, let me know and I will try to help.

Regards
Randy

Thanks All,
OK,........ Well I can't move the tank back as it's already agains't a former and I just switched to 10% nitro and it definitly has more power over the 5% nitro. The way the engine breaks and the location of the plane when the motor breaks is still about the same regardless of which nitro I used........SOOooo, I was thinking maybe if I remove the muffler pressure to the tank and make the engine suck it's own fuel that it might increase the break or at least the location of it anyway. If I'm doing an inside loop the engine breaks at around 11:00 o'clock and returns to 4 stroke at around 1:00 o'clock, and the reverse for outside loops. But if I allow the fuel flow to vary more by removing the muffler pressure it might break sooner ?...... I think I'll give it a try.........Whatcha think
                                                 

Thanks All,
OK,........ Well I can't move the tank back as it's already agains't a former and I just switched to 10% nitro and it definitly has more power over the 5% nitro. The way the engine breaks and the location of the plane when the motor breaks is still about the same regardless of which nitro I used........SOOooo, I was thinking maybe if I remove the muffler pressure to the tank and make the engine suck it's own fuel that it might increase the break or at least the location of it anyway. If I'm doing an inside loop the engine breaks at around 11:00 o'clock and returns to 4 stroke at around 1:00 o'clock, and the reverse for outside loops. But if I allow the fuel flow to vary more by removing the muffler pressure it might break sooner ?...... I think I'll give it a try.........Whatcha think
                                                 

Greg, I believe that you stated in your first post that the engine was insensitive to nose up positions so I can't see that changes with the fuel system will give you the results that you want, although it doesn't take much and would be worth trying for the sake of seeing what happens. It really sounds like the engine is just running too cool to respond the way you want.

I would try the following one at a time and see what happens and then go back to your current configuration and change the next thing.

You've tried nitro content and not much change so go back to your standard fuel.

Increase the prop size. Most .40 engines will turn 11" props (maybe an 11 X 5) without much problem. This will increase the engine load and operating temp.

If that doesn't do it go back to original prop and remove a head gasket. (I would bet there are a few gaskets under the head) Increased compression = increased operating temp.

If both changes move you toward your goal but not enough... try both.

It could be as simple as where you are setting the needle to get the lap times you want. You might be too deep (read rich) in the 4 - cycle mode to get a quick response. If so I'd drop to an 11 X 4 (I like Pro Zingers) and lean it out a bit.

All of these suggestions are what Randy has beem saying in his posts.

Thanks Randy, Dick, & Bill,
I will try some of these things this coming weekend weather permitting. It's rather odd that when flying, my engine breaks so late because when I am just runnning the engine I can lift the nose of the plane up and it will break and when I lower it back down it goes back to 4 stroke. From now on I will pay closer attention to the needle and tach settings. I thank you all for sharing your knowledge, much appreciated.