My favorite 2 stroke. Mine lives on 10 percent with added caster. Some SF’s had a reputation for peeling the liner. Mine is good to go after 3 gallons. I use 4 oz of extra caster for a total of 20 percent oil. 12x6 APC nets me 11,000 peak.
Years ago i had a 60 fp i thought it ran really good. I wished i still had it, its cool you trying motors out, and i love the throttle handel you made thats cool.
I love the SF61. I have 3 (ABC and ring) and they run really great. Great power on pipes at relatively low rpm. I have one ABC SF61 achieving superlow idle of about 1200 rpm. Peak rpm is 11500 at 12x8 on a pipe (test with 13x8 was 10000 but pipe was set up too short so I took a smaller prop for flying).
The superlow idle was on a 14x6 APC. Even my 4-strokes did not achieve such a slow stable idle. May be the Laser 100 on a 15x7 Robbe prop idles as low at 1300 rpm.
@@davidsai Sounds like the setup I fly on my low wing trainer. If you want speed you should use an APC 12*8 but every pipe setup is different. Ground rpm 11-12000. If the model is not really going fast (stick may not go realky fast) you can try 13*6 or 13*7 as long as the engine is happy and the pipe setup is long enough to support lower rpm.
There is no one ideal prop size. Props are one thing you need to experiment with. 60/61 size engines generally use a 12x6 but other props should be tested based on the type of flying you do. All engine instruction manual will list the recommended prop sizes for the particular engine.
I'm very interested in the function of the carb, I've never experienced that type before. Just got a .46 sf myself, i'll have to start looking for a .61 sf to add to the collection!
The OS 61FSR has a bore of 24mm and a stroke of 22mm making it over square. The OS 61 SF has a bore of 23mm and a stroke of 24mm making it under square hence a square bore/stroke would be equal measurements. These measurements along with port timing and pipe configuration will determine where the usable power delivery (powerband) will exist in a 2 cycle engine. Over square engines are noted to rev more freely and have a greater concentration of power near its peak. Under square engines are noted to produce more usable torque lower in the rpm scale. There is much more that goes along with 2 cycle theory, but that sums up your question in a nutshell. The 61SF makes its peak torque 1000-1500 rpm lower than a 61FSR but swings a larger prop.
