I have run 3 tanks through at 2 1/2 open nedle valve at 4000 +/- rpm as recommended. had to leave glow started on. what reduced needle valve setting should I do next? what would be a typical full break in setting? Do not have a rpm meter so will go by sound. thanks for the help..

Practical Needle Setting from Bill Baxter at Great Planes.

Any model engine, once it can be run on the test stand while leaned out to peak RPM, can be used in any application. When used in an airplane, the needle is leaned until the engine is at peak, and then richened somewhat. This extra bit of richening is done because the engine will have a tendency to lean a bit as the fuel tank is drained.

The engine leans as the fuel tank is drained because a full tank has a higher fuel pressure than an empty tank. The difference in the height of the fuel between a full and an empty tank causes this. It's called a change in the fuel's "head" pressure. As the tank drains, the head pressure will decrease. High-"G" maneuvers will also cause fuel pressure to lower. The high "G's" will pull the fuel away from the engine, which leans the mixture.

Running an engine just rich enough to prevent it from going past peak is the goal. That way, it will never run too lean in the air. On a four cycle, you should make sure there is a smoke trail left by the exhaust.

As different weather patterns move across an area, atmospheric pressure will change. Therefore you cannot rely upon an engine to keep the same needle setting from day-to-day. It must be checked every time the engine is run. Sometimes, the setting can change dramatically during the day, as air temperature and humidity change. It's a never-ending battle to keep the engine properly-set and healthy.

You can always tell if an engine is leaned to the rich side of peak RPM by using the "pinch" method. Just give the fuel line a pinch and quickly let go. If the engine's RPM increases, you can lean the engine further. If the RPM remains the same or drops, you must immediately richen the engine…it's too lean. Generally, you want to have a slight increase when you pinch the line and the engine's running at full throttle.

If you cannot get to the fuel line because the engine's cowled, the best way to check for proper leaning is to run the engine at full throttle with the fuel tank about 1/4 full. Lean the engine to the desired point and then pick up the model and hold the nose straight up. The engine should pick up in RPM. If it picks up a lot, you can lean the engine a bit more. If it stays the same or drops, you must immediately richen the engine.

Because the engine tends to lean as the fuel level in the tank drops, adjusting the engine for conditions near the end of the flight will keep you from damaging your engine.

If you then fill the tank and your engine runs very rich at the setting you just found, then you have a fuel tank location or fuel feed problem. Large mixture changes during a flight are not good. You'll need to find out what is causing the problem.

Thanks for the imput. have gradually reduced high speed needle from the break-in 2 1/5 open to 1 1/3 for good top end rpm. with 300 rpm drop as you suggest with richening a little. very rough idle that stalls if below 3500 rpm. should I start the low speed needle adfjustment now.? spec. says rpm from 2000-12000. is it realistic to expect a 2000 idle?

2,000 is do-able, the low speed needle will have to go in quite a ways, do it 1/8 turn at a time until you get what you want. About every other time you lean the low speed needle check the high speed needle again, the two needles effect each other somewhat.

Hobbsy of course is right. 2000 rpms is do-able but depending on the nirto content may be a bit difficult to obtain on a new engine. Shoot for 2300-2500 till you get a gallon or so through it and then start to fine tune the low end. You've chosen a great engine. You'll be happy.

Yea you are going to have to go in a bit on the idle valve screw. I have that same engine and was kinda frustrating. Kept stalling under3200 rpms. Then I started to really turn in that screw, looking at 2800 rpm. I liked the faster idle just cause I was worried about it stalling, supose I could go lower. Youl know when youv gone to far too, the engine wont transision well at all. Im not so sure the smoke thing works so well on the motor, as your throttleing up if its too rich you will see a lot of smoke?