super tigre 0.61 tuning difficulty
 

I have a super tigre 0.61 on the nose of my big stik 40, that I've been flying for a few months. I actually more or less learned to fly on it .. anyways, I can't get it to maintain a reliable idle, it always loads up and bogs down under power or will not stay running at all. It's about as old as I am ( 16 ), so is it an age issue or am I just a poor tuner ?

Either way, does anyone have some advice to offer ?

super tigre 0.61 tuning difficulty
 

Practical Needle Setting

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.

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 to Bill Baxter, our service center manager, for this and many other great tips for r/c engine operation!)

super tigre 0.61 tuning difficulty
 

SuperTigre

To properly set up your carburetor, there are a few steps...

Make sure the spraybar is set so that the fuel slot is pointed straight down the center of the carburetor. You will have to look through the carb from the bottom, with the venturi opened to full. Loosen the two screws next to the high-speed needle valve to rotate the spraybar so that the slot is centered.

The idle needle can be seen in the slot of the spraybar. It looks like a piece of wire that has the end squarely cutoff. It should be less than one-half way across the slot when the venturi is opened to full.

The high-speed needle should be opened about 2-1/2 to 3 turns out from closed.

All of these settings are very rich. You'll have to start the engine at about 1/4 to1/3 throttle. Once the engine starts, advance the throttle to full. You can then lean the high-speed needle until the engine is running just rich of peak RPM.

Once you have the high-speed needle set, you can retard the throttle a bit and use the idle needle to adjust the engine. Retard a bit, and adjust. Keep doing this until you have reached the desired idle RPM and mixture. Remember, since we started out with an intentionally-rich setting, the idle mixture will have to be leaned.

Finally, the midrange can be adjusted by rotating the spraybar a hair. Just loosen the two screws next to the high-speed needle and rotate the spraybar just a tiny bit. Either direction is OK. This will help you get a good transition and midrange.

We use an O.S. #8 glowplug, although a lot of people have had success with the O.S. Type F glowplug. We recommend you try both to see what works best for you.

Many people like to use larger volume fuel tubing to feed these monsters to avoid the chance of insufficient flow. This works quite well and is also recommended.

Sincerely,
Mrs. AnnMarie Cross