pelham,

The tank position is a possiblity but you may need to a little more diagnosis.

If it is only on takeoff then I would think the low speed needle is a little rich.

Try this. Make sure you are holding the plane really good

Start the engine and let it warm up. Now throttle up quickly to only 1/4 to 1/2 throttle. Does the engine hestitate, and spit fuel out of the muffler?

If so the low speed needle is too rich

If doing the above and the engine hesitates, does not spit fuel and dies or almost dies then it is too lean.

In a too rich setup turn the low speed needle 1/8 turn clockwise and try this test again

If it is lean turn the low speed screw counter clockwise 1/8 turn.

Keep doing the above until is goes to half throttle smoothly and quickly.

Once that is done then go from idle to full throttle, again if it spits fuel and hesitates the high speed needle is rich, it it tries to die it's lean

Based on your description, it sounds as though the low speed is rich...