Hi Guys. I just found this thread and I must say it is very informative. I would like to share some experience I had with my ST-2300 in hopes that I am adding some useful information to this very informative discussion. Last year I purchased a used Excelleron 90 with a ST-2300 up front. The plane came with a uniflow tank system in it, and this was my first encounter with this type of fuel feed. I read every thing I could find here and elsewhere on this type of fuel system. After extensive research on uniflow tanks I thought I understood the concept very well. However after many attempts of trying to get a good needle setting on the 2300 I was stymied. The engine would go lean and then rich without me touching anything. I checked everything I could think of for air leeks and found nothing wrong.

The plane also had a KS canister muffler with a pressure tap on the input pipe just before the large diameter of the canister. When I disconnected the pressure line from the muffler and opened the top vent to the tank, the problem changed to a lean top end and a rich idle and a rich low to mid range. I thought that muffler pressure was the problem but had no way of measuring this pressure. I had heard that GOOD muffler pressure was between .5 and 1 psi, which is not much at all. Not wonting to spend $500.00 plus for a micro-manometer I made a simple U-tube manometer using a wood yardstick, fish-tank tubing and fittings from Wal-mart. Total cost about $10.00. This simple manometer will read up to one PSI, is calibrated in tenths of a psi and reasonably accurate to within one-hundredth psi. I use a T-fitting between the muffler and tank to read the pressure. It works better than I expected. I now can read and see what muffler pressure I actually have.

With this new ability I found the exact problem. The fitting at the input pipe of the muffler was perpendicular to the high-speed hot exhaust gases and sometimes causing a positive pressure and sometimes causing a negative pressure. I removed the fitting and cut the end on a 45 degree angle so that the hot exhaust gases would go into the fitting and pressurize the tank. Much like an air ram. It work very good and I now have a steady .4 psi at WOT and about .05 psi at idle. I am still having a somewhat rich midrange. The reason for passing this along is that if you take an accurate reading of muffler pressure with the stock ST muffler and then pinch down the tubes on the Pitts muffler to obtain the same pressure reading the engine should perform as designed.

So, with a new carburetor that sucks more fuel and higher muffler pressure to push more fuel we will get these ST 2300s to run like the high dollar engines.

I still cannot get the uniflow tank system to work to my liking, but I learnt a lot trying.

Old Bob