You have tried new plugs?
If not, the next cheap check is to go round all the connectors (esp. the earth / ignition ones), pull them apart, squirt with your favoutrite water dispersing spray, and either open the bullets up slightly with a small screwdriver or squash the recepticales slightly with pliers to make sure they have a good contact and give each one a good tug to make sure it's still firmly connected to it's wire. Any with corrosion, clean thoroughly.
Next stop is probably a recoil starter-ectomy & see if you can get in to check this lot http://store.brownspoint.com/pdf/DT2...T28(80-82).pdf
(page 13 of the PDF) and see if anything has come adrift / fried in there. Looking at the Ignition coil etc, are those cables integral to the coil unit? Those multi- part plug caps look like another potential failure location to me!
No idea on the theoretical comp on those engines - but that's almost a 9% difference. It's premix, so in theory both cyls have similar oil content. Right now it's a bit irrelevant without the spark! If you can get a replacement gasket, pulling the exhaust cover off will give you a basic visual of the state of a section of the pistons & rings. The damage on a 2- stroke is mosre likely on the exhaust side.
If you are totally stuck, I have a DT25 (or 30) of the 1993-> version (3 pot, auto mixing longshaft) which I am now happy enough with the Merc's running to sell. But I bet making yours go again is doable and probably cheaper.