there are yellow 4 stroke GTX (03 or 04 I think...) , but from what I can tell by looking at that its the 951 the giveaway clue is the hood the 4 stroke hoods are different than the 2 stroke.
cant you just look inside gas cap and if there is an oil/gas mixture ratio, then it is probably a two stroke, 4 strokes there is no fuel oil mixture....