Had a similar issue with the same motor at our club field here. We ended up putting one of the Iron Bay regulators on it. Motor problems went away. Turned out the motor just was not consistent at drawing fuel. Go to www.ironbaymodelcompany.com and look under accessories. The advantage of this regulator is that it will not let the motor flood. Fuel is forced to the back of the regulator, and sits there until the carb draws it up. Has helped in a lot of U Can do 3D as well where the tank is mounted very high.

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