Dan, not sure I fully understand. Are you saying you have had good luck with 4-strokes (on a CL application) with the throttle maybe 66% open (to simulate a venturi restriction), then adjust the needle for desired full speed?
Or if the engine is not running well at full throttle (due to air leakage), test and start to close the throttle to see if the engine performance improves?
Thanks in a advance.
That is exactly correct. Search out threads on here by Bob Reeves. He and some others did a lot of research and experiments into this. You could also go to the Tulsa Gluedobbers web site and a lot of it is posted there. Bob has since passed away but he left a lot of information behind. Bob advocated for the low RPM/high pitch prop method of running 4 strokes. If you happen to have a C/L venturi on an engine, he came up with the idea t add a screw to the throat of the venturi that goes in on one side only, and by running the screw in and out, you effectively change the venturi choke area. Running it in makes it smaller and draws more fuel, out makes it bigger and draws more air. Not really a new idea, the speed limit combat guys have been doing the same thing for a long time to get their engines to run a constant speed.. As you turn the screw in, you turn the needle in next to get a max RPM setting just above 8000 RPM. That is what he said to do for a Saito 56/62. props are in the 6 and 7 inch pitch range. If the weather gets warmer, you can screw the blocking screw out just a bit to let more air in and reset the needle. When it gets cold out, you do the opposite, screw in in to let in less air and reset the needle. It will kind of go against everything you already know about engines and props for 2 strokes, but it works. With an R/C carb, the barrel takes the place of the screw. Just play with it and get familiar with it. For a 4 stroke that small, i don't know if you need a new RPM range or not, but just experiment, go by lap times and line tension. before you try any maneuvers. The engine might not sound like it will pull your hat off your head, but just ignore that and go by lap time and feel. This set up with muffler pressure will make the engine run very consistently where ever it is flying. You will have to get used to that and if you have been flying 2 strokes for any length of time it will sound foreign to you. The 4 stroke is a different animal, and resist all temptation to run it like a two stroke. This low RPM set up lets the engine get plenty of fuel, and thus it runs cooler. I have run several gallons of fuel through my Score and Saito .56 and all of the chrome is still shiny. I ran all of this by Gilbert Berringer from France. He is one of the top stunt pilots in Europe and helped bring the 4 stroke engine along. He has a large manufacturing company that makes aircraft wheels and brake systems, and comes to Oshkosh every year, along with Sun and Fun in Florida during the winter. He flew my Score several times and was impressed by it. He sets his engines up with a very small venturi to start with, no bigger that 6mm, he told me, and when you put a spray bar through that, the choke area is pretty small. I run Powermaster YS-20/20 for the most part, and it's getting pricey now, but i only use about 3.5 ounces per flight, so it lasts a while. Try some of the Powermaster synthetic blends in the 15% range. It would not hurt to add some extra synthetic oil to get the total oil content up closer to 20% like the YS blend. I have been trying not to add any castor, as there are a LOT more and smaller moving parts in these engines, and even smaller yet for your .26. If it sets up and runs the lower ROM ok, it might not be necessary. It will take a lot of attention on your part as you go through the motions. Everything from starting them to picking props and setting the needle will be different and again, the big thing is DO NOT run it like a two stroke!! The closest thing I have to your engine is a Saito Black Knight .30 but I have yet to pick a model for it.
Type at you later,
Dan McEntee