Maybe take a look at Toni Clark's website. He has adapters, both cast and fabricated for 2 strokes using Walbro carbs. Perhaps not to buy from him, but to get an dea of what is available and what works. Again these are for two strokes, but I think four strokes are less sensitive to intake and exhaust header length. I could be wrong, though. I have several Ryobi 4 strokes, I am going to convert for plane use and I am looking for a Stihl 4-Mix to convert. Good luck.

http://www.toni-clark.com/ftp/cat_11..._1_2010_en.pdf pages 84 and 85

Sincerely, Richard