If you just bought your first big engine, it probably looks awesome and very complicated. Don't worry, most of the biggies are 2-strokes which have only 3 moving parts so they can't be very tough to figure out. They have a ringed piston like the smaller model airplane engines and also two adjustment needles on the carb. It is a pumper carb, but if you forget that, it won't bother you. They do (most of them, anyway) have spark ignition instead of a glow plug. Your lawn mower runs OK, doesn't it, (better than mine, I hope) and it has spark ignition. And finally, you have to mix oil with the gas, which is a lot cheaper than glow fuel. As a matter of fact, most of the big engines are pussy cats as long as you don't get your hand or anything else in the prop.

Let's go to the carb first and discuss it. The most popular carb is the Walbro. I have 4 engines of 3 different types (Zenoah, Webra Bully, and Sachs-Dolmar) and all of them came with a walbro carb. There are several other types of carbs, but most all of approximately the same size are interchangeable on the same engine. There are 2 needles, usually marked H for high speed (this corresponds to the large needle valve or a regular model engine) and L for low speed (this corresponds the idle needle, usually on the other side of the carb from the big main needle valve of a regular model engine). There is also an idle stop screw to limit how low you idle the engine. This is just like the one on top of the carb of a regular model engine.

Install the engine per the manufacturer's recommendation. Hook up the fuel lines, being sure to use a filter. I don't care how clean and neat you are, you can't keep all the grit out of your tank so filter the fuel just before it gets to the engine. Put on the correct size prop. For the 35cc sized engines, I like the multi-pitch 18/6-10 props. The 20 and 22 6-10 props work well on the larger engines.

To start, I go through the following procedure:

1. VERY IMPORTANT!!! Tie the tail of the plane to a stake or something or have someone hold it. Don't have a rookie hold it, I mean someone that has never heard a model engine before. If you start and they are startled and turn loose, you could get eaten. Just think of your engine as a lawn mower turned sideways with you standing in front of it.
2. Make sure that the kill switch is in the "stop" or the "off" position.
3. Open the carb and choke the engine, turning the prop over 3 or 4 times. Next, flip the prop about 4 times to get some fuel into the cylinder.
4. Close the carb, but run the throttle trim to the high position. Don't try to start at full throttle.
5. Place the kill switch in the "run" or "on" position.
6. Remind your holder to get ready, then flip the prop or wind it backwards and let it go. Two or three flips or spins and it should start.

Some engines with CD ignition have to be flipped very hard or some type of starter used. They don't make enough spark and hand cranking rpm to fire the gas. Quadras and Sachs engines with electronic ignition need a starter, usually the spring type that goes on the rear shaft. The points versions of these two will hand start OK.

Idle the engine down. Don't try for a real slow idle on a new engine. Tell your holder first, then run up to full throttle. Not whether it is rich or lean. Maybe I'm squeamish, but I do all my adjusting with the engine shut down. I know some of the engines have rotated carbs, but that's a big old prop. At any rate, adjust the top end to run slightly rich. Now you are ready for a test flight.

On new engines, I run slightly rich for 4 or 5 flights, then slowly lean the mixture over the next 6 or so flights. I never set the engine for max power before take off. It will lean out some during flight and be too lean at the end. I have found that if I run slightly on the rich side of max rpm (the engine still sounds lean), my engine will normally run flawlessly and last forever. And, this is the good one; you will rarely have to make an adjustment.

I also feel that you can only get a good needle valve setting by flying the plane. My experience from competition in CL rate race and combat and RC pattern and quickie 500 has been that you need to hear the engine in the air after it has flown 6 to 8 minutes. If it runs well at this point, the needle is correct. If not, land, shut down, refuel and make a small adjustment (1/8th turn) and try it again.

Be careful and good flying.