Thank you guys for the replies, as always great tips. Is one still able to find new rings for the Homelite 25 cc to give it a little more pep? How easy are these engines to hand start? or an electric hand starter will do the trick? Or perhaps I should forget about this engine (which needs a lot of metal cutting and finishing) and convert a 31 cc Ryobi instead, which having rear carb and exhaust makes it ideal for R/C use as everything stays inside the cowling (and with no metal clean up). Which other engine with larger displacement, like 45 cc or so do you recommend for conversion, where the necessary attachments are being offered in the market already for such purpose? I hear about the Poulan, is it one of the better ones, I'd like those that hand starts easy or a spring starter can be attached to the rear shaft. What say you?