I am hoping that someone can help me out.... I just purchased a Seagull Decathlon powered by a Evolution .46 with a Bisson Pitts style muffler. I think I am having a fuel delivery problem. The plane runs like a champ on the stand, however, when I pick it up and put in a nose high attitude, the engine leans out and dies. (Yes, we have tuned the engine)

I have checked everything I can (with out modifications) i.e. checked fuel tank for leaks, replaced all fuel lines, ran with and without the cowling etc.. but this thing just won't run right. One evening at the field, it ran like a champ but the next day, I put the cowling on and the same symptoms occurred. I called Horizon to ask if they have heard of this problem before and they say they have not. It is hard for me to believe that I have the fist case of this. I have read that sometimes pitts mufflers don't push enough tank pressure. I would like to try to fix this problem WITHOUT a perry pump or plugging one of the exhaust ports. Does anyone have any suggestions? Comments??

Thank You!!

A Perry pump or Cline regulator or close up one of the exhaust ports or put the stock muffler back on are the only options.

Enjoy,

Jim

I put a perry pump on my moki 1.35 in a funtana 90 with a bisson pitts muffler due to this problem. It did instantly solve the problem and transitions as fast as you can move the throttle stick now. You can also put a check valve on the pressure line from the muffler to the tank so only pressure goes into the tank and does not escape, you just need to put a fuel T between the check valve and the tank with another line hanging with a plug in the end. This will allow you to release the pressure in the tank after flying and can be used as an overflow line as well. One other thing you can do is block off one of the down tubes on the muffler to create more back pressure, creating more pressure to the tank. Hope this helps

let you engine come warn at the ground with a little rich set (high end) put your plane nose up and open full throttle to see if your engine come lean nose up, if it come lean ,make your high end more rich
if that way does nt work you have to close one exhaust port.
using a check valve is a good idea to keep pressure when the engine is slow and this way the transition wil be much better

to post from Jim and lafus maximus they are right , I just comfirm

let me know if your problem is not fix after you try this

Gilles

Thanks for the input guys! Problem has been fixed.

Tell me if you have ever heard of this.... My buddy at the LHS said he read some where about a "double clunk" method of pressurizing the tank. Basicly, the exhaust pressure line is fitted with a clunk inside the tank with slightly shorter tubing than the fuel pick-up line. Exhaust pressure is exited into the fuel (pressurising the tank from the bottom instead of the general top method) I thought is was a pretty stupid idea to be honest with you, but I figured what the heck! I would try it before I tapped my crankcase.

Well, I don't understand it, but it worked like a champ! (sitting here scratching my head)

Let me know if you have heard of this before.