I have a 3500 that I have been using occasionally for eight years. This engine is sensitive to tank placement and to a smaller extent, nitro content. Use the smallest tank you can, I use 16-20oz and make sure its mounted on center with the spraybar. It will run fine on 5% with great fuel economy, BUT the needle setting will change a lot as the tank empties. 15% makes the needle much more steady throughout the flight and during high G maneuvers. Setting the needle is different from smaller engines in that it MUST BE ON THE EDGE OF FOURCYCLING with a full tank!!!! If you lean it beyond that it will get hot and sag in flight. The low speed needle is adjusted for low idle because it is a little rich in the mid range, just keep turning it in until it tries to die out at idle then open it a little. The slow idle will be choppy but is reliable. Starting this engine is super easy, if its cold load it up with fuel and flip it backward, if hot flip forward. Do not flip through compression when cold because it can bite hard. Prop for 7500-8000rpm, it runs out of steam fast above 8000 and looses fuel draw below 7000. It will take 5-10 gallons of fuel before its fully run in.