This morning I made several fast-taxi runs in my Lanciar 235/O-290-D2. The first few runs were with empty wing tanks and it got real squirrely. The plane would veer from side-to-side with a period of about 3 seconds and it was all I could do to keep it on the runway. I got scared at about 50 KTs, pulled the power, and applied the brakes heavily to keep from going into the weeds. I never could get going fast enough to lift the nose wheel.

I taxied back to the hangar and added 5 gallons of 100LL in each wing tank and repeated the test. The results were much better but the side-to-side oscillation was still there and it was easy to get into a P.I.O.

Is this normal behavior for the small Lancairs? Could this be due to something in the oleo strut? (I don't have the centering mod)...Tire pressure?...Dragging  MLG brake?...Any other ideas?

FWIW, I added a 5" ventral fin and extended the rudder 5" to avoid just this sort of thing with the larger engine. Apparently, those mods don't work at low speeds.

Help!