RE: Desert Aircraft - Super!!
DA are lovely engines and id agree even in the UK service is excellent, though the model for service delivery is rather more convaluted than in the US. However, I would point out that customer service in the US is generally better on most things than in the UK so our view of things tends to be rather different. More and more these days there is not so much to choose from between the engine manufacturers and what wins the sale and customer loyalty is actually after sales support and service (it certainly works with me, ill gladly pay 20%+ more if the service backup is there to compliment it). What has often turned a nice model/engine combo with potential into a nightmare for me in the past has been poor information, support and service. In europe generally we need to learn this more... (incidentally, I know a 3W dealer well in the UK and there service is also excellent!)
On the 75-80cc question, whats wrong with the DA-100? I fly an 80cc CAP on a DA100 and it works well, it needs the extra weight (though the DA100 is alight engine for tis size anyway), the 100 twin is nice and smooth with plenty of torque. If I were DA i dont know that id bother making a 75cc single. I guess the only reason to go for a single would be cost.