I think the ES-55 pipes are a little small for the 62cc cylinders of the GP123, coupled with the fact that I've been really beating on this combo... The pipes have started to leak exhaust through the epoxy/weave of pipes and have turned brown.
I was talking to Lorne and he has some new no-name pipes that look very, very similar to the SmoothPipes at a whicked price.
Here they are next to the ES pipes. Over the next week I'll be testing these on the Gp123 at various header lengths to see how they perform