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G-3250 (SUPG0268) Tech Notice

Breaking in the SuperTigre G3250 and Setting Its Carburetor

Some customers have complained that the G3250 runs too rich in the midrange, or has other operating difficulties. That's due to an incorrectly-set carburetor, or the type of fuel used. Setting the carburetor is not difficult, but several steps must be performed properly.

A new engine should be broken-in on a test fixture. We use a 20x8 Zinger prop, a high-oil fuel with 5%-10% Nitro (we like Omega 2-stroke, don't use Cool Power, the engine likes castor oil), and the stock SuperTigre muffler for the S3000K (which works great!).

Break in

Break-in running should be performed on a test fixture, up off the ground. Don't use your model for a break-in platform.

Use a good quality 2-stroke fuel with 5%-10% Nitro content. Castor oil in the oil blend is highly recommended. Use a 20x8 prop and a muffler. Start the engine with the high-speed needle about 2-1/2 to 3 turns out from closed. Start at 1/3-1/2 throttle. Don't even try to start at idle because the engine probably won't run that low at this point.

When the engine starts, don't remove the battery from the glowplug yet. The engine is probably running very rough, cutting out and surging. Open the throttle to full. The engine will still be running very roughly. Slowly lean the high-speed needle until the engine just stops cutting out and surging (at full throttle, remember). The engine should be running fairly smooth at this point, but still very rich. The RPM should be in the low 6,000's (or high 5,000's). Let the engine run this way for about 24 ounces of fuel, or about 15 minutes, all at full throttle. Adjust the high-speed needle to keep the engine running at this speed.

After the first 15 minutes, or so, of running, you can start to lean the needle towards the peak RPM setting. Have the engine running as in the first 15 minutes. Lean the needle about 1/8 of a turn. Listen to the engine. If it picked up a bit, that's OK. Did it sag? Then richen it again. It should pick up. After about a minute, lean it some more.

The procedure isn't really cut and dried. We usually lean a bit, richen a bit, lean a bit, richen a bit, gradually getting leaner and leaner, but never allowing the engine to sag in RPM as we lean. It should take about 15 minutes or so for you to lean it to the point where the RPM will level off as you lean. Don't go leaner than this point. If you lean to the point where the RPM sags, richen immediately. If the engine gets too lean, it will heat up rapidly and become damaged. Once the engine can run out a full tank of fuel while leaned to peak RPM, it's ready to have the idle mixture adjusted.

Setting the Idle

The idle needle should be open far enough so that it blocks no more than one-half of the slot in the spraybar at full throttle. The slot in the spraybar should be aimed directly down the center of the carburetor. Some modelers have turned the spraybar to move the fuel nipple to a better angle. DO NOT do this...it greatly affects how the engine will run.

Once the fully-leaned-out, peak RPM setting has been found on the needle valve, slowly close the throttle to locate the idle mixture setting. Adjust the idle mixture setting until an idle of 2,000-2,200 RPM can be easily sustained.

Open the throttle. If the engine hesitates and blows out a lot of smoke before it comes up, or it just quits, it's too rich. Stop the engine. Lean the idle mixture 1/4 turn, open the high-speed needle 1/2 turn, and restart the engine. Open the throttle and lean the high-speed needle to peak RPM. Close the throttle to idle. You may have to adjust the position of the throttle arm with the idle stop screw or your transmitter trim to get an idle speed that will hold. Throttle up. If the engine is still too rich in the midrange, just repeat the process. Eventually, you'll get a good setting.

If the midrange is too rich, then the idle mixture is too rich. However, leaning the idle mixture will affect the mixture at full throttle. Both high-speed and idle needles affect each other. If you lean one, you'll likely have to richen the other. That's why the high-speed needle is richened when you lean the idle needle. You then re-set the high-speed needle to allow for the change you've made in the low-speed needle. The top-end RPM may change a little, usually dropping about 100 RPM or so, but that's normal.

It can take about 15-30 minutes to get the engine setup once it's had enough running to allow it to run out 16-24 ounces of fuel at full-throttle, leaned out to peak RPM. If you've spent less than an hour running your SuperTigre G3250 before putting it into the air, it's probably not ready to fly.


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