c_locklair wrote:True Dave, one head bolt was completely loose out of the box. I'll take it off the plane and break it down to look at it. I am getting a little black goo where the pitts meets the exhaust too, can't get it any tighter. Can you use a little gaskicinch there or some other sealant? I'll tighten everything down good, when I put it back together. I'll do that over the weekend and give a report. Dave, do you think I should plug one pitts pipe or not? Again my avitar thanks you.
If one head bolt was that loose, then I'm betting there are lots of other loose parts on that engine too.
Black goo almost always means metal is wearing against metal. Some high temp RTV or silicone between the engine and the pitts muffler should cure the problem.
Most pitts mufflers don't produce enough backpressure, so the high speed needle ends up being opened a lot to compensate for the lack of muffler pressure. In a vertical climb the engine goes lean, and in a vertical dive the engine goes rich. At half throttle it's even worse. The 55AX won't stay running if the mixture gets too lean or too rich, and having the needle too far open only aggravates the problem.
To find out for sure if the pitts muffler exhaust tubes need to be pinched down or plugged, first run the engine with the stock muffler and set the high speed needle valve, then count exactly how many turns open the needle needs to be. Remove the stock muffler and install the pitts muffler. Pinch down or plug the exhaust tubes until the high speed needle ends up open the same amount as with the stock muffler.
I always keep the avatars turned off, so that's the first time I'd seen it.