Nearly all RC engines use fairly simple, suction type carbs. A few of the very expensive engines use fuel pumps and/or regulators.

The OS .61FP is an entry level engine with a very simple, "air bleed" carb. The large needle valve controls the fuel mixture for high speed running. As you throttle down, air is closed off reducing power. There is no mixture adjustment as you throttle back as there is on more expensive engines. You do get some since the reduced carb throat size gives less suction for less fuel draw. DEspite this, the mixture is too rich at idle for the engine to run well so an additional port for more air was added to the carb. This is called the "air bleed" hole. As the rotating carb drum gets very nearly closed, it opens the air bleed hole making the idle mixture leaner. You adjust the size of this hole to set your idle.

Looking at the front of the carb, there is a small hole right in the center. This is the air bleed hole. The screw on the side with the spring on it is the adjustment screw. A good rule for a starting setting is the screw should cover half the air bleed hole. You need to look in the hole and change the screw so it is half way across the hole.

You will need good fuel and a good glow plug. RC fuel contains alcohol which absorbs moisture fron the air. Old fuel may not run well. I have had people come up with fuel they have had in their garage for 3 years. If yours is like this, toss it and buy a new gallon.

Make sure the glow plug is good. Just because it glows does not mean it is good. It is platinum and is a catalyst just like the catalytic converter on your car. The element can become coated and contaminated and will not ignite the fuel after the battery is removed. if your engine has been sitting a long time, get a new plug. An OS A-3 or some other sport RC plug will do.

Next, open the high speed needle, the big one about 3 turns. Set the carb about a quarter open and try to start the engine.

Given a good plug, fresh fuel and the air bleed set half way, it ought to start. After you do get it running, leave the battery on and run it up to full power. Turn the big needle valve in until the engine peake, then open the needle about a quarter turn. That is a good flight setting if you have no one to help you.

You really need to check with the local club and get some expert assistance.