RE: Opposed twin cylinder engines.
RJ:
That nipple below the cams is the crankcase vent. It should have a length of fuel tubing stuck on it and run out the bottom, it needs to be at least 4" long to keep the engine from sucking trash (dust) back up through the vent.
Some people prefer 20% nitro fuel, but I've had very good results using 15%. One place I differ with many though, is in the use of pure synthetic oils. The 18% is fine, but 3-4% of the fuel should be castor oil. Even Horizon/Saito recommend a castor blend, specifically suggesting Omega or Powermaster fuels for maximum engine life. My choice is Omega, but I'll admit it's because I have a good source for Morgan fuels.
If you have a supply of fuel with straight synthetic oil just go to your local food or drug store, USP castor oil is easy to find. Dump 2-4 ounces in each gallon you have, all is then fine.
Saito engines want to be slobbery wet with prime for a cold start, and they (for me) start best at about 1/4 throttle. Start with the HS needle 3 1/2 to 4 turns open, when the engine is running let it warm a bit, then go to full throttle and peak the HS needle, then richen it to get 300-400 rpm drop. Check the transition from idle, if you have to adjust the LS needle any amount recheck the HS. The LS needle (on the two needle carbs) has a large effect on the HS.
If yours isn't one of the last of the FA-270T engines it will have an air bleed carb. Saito AB carbs are different from most in that they incorporate a fuel regulator valve in addition to the needle valve, it sets the low and mid range mixture. The smaller carbs have no adjustment on this valve, the larger ones do. There's an index mark for the starting point. See pictures. Leave it on the index mark unless you can't get it running right with the use of the HS and air bleed adjustments. I'm not going to try explaining its adjustment (too long an operation) but usually it's fine at index.
HTH. At least a little.
Bill.