Steve Campbell,

The specs on the Wild Hare site are:

.91 to 1.20 2 stroke,
1.10-1.25 4 stroke, 26cc gas

Unless your referring to the airframe being maybe to light there should be no problem with a 26cc gasser on a plane this size. I had the older Brillelli 26cc SPE engine on a CMP Giles 202 that is the same size and there was no problem at all.