Last week I succumbed to a spot of eBay therapy and accidentally bought a little OS 10FP 2 stroke. It was listed as good condition, but apparently the owner had never made it run properly. I’ve always quite liked the idea of a small glow engine and figured maybe trying to get it to run OK would be a bit of a challenge, so I placed a bid and won the auction. I think I got it for a good price considering it was essentially a non runner so if I could make it work I’d have a bargain.

When the thing arrived I was impressed by how clean the casing was and found it turned over ok, with good compression. The carb. seemed to move fine and there were no visible blockages, so I wondered what could have caused the problems the previous owner had experienced. While inspecting it I discovered both the silencer and the cylinder head screws were absolutely buggered, somebody had clearly been at them with a screwdriver and now a Philips head driver was just happily spinning in the heads. Right then, clearly some filling action was going to be needed to get them out and new ones would need sourcing. After a bit of a struggle I got all of them out, measured them and ordered new ones (M2.5 x 10mm for the head and M2.5 x 25mm for the silencer).

While inspecting it with the silencer off I noticed the transfer port in the piston was facing the exhaust port, not the matching ports in the other side of the cylinder casting! Somebody had taken it apart  and put the liner back in the wrong way round which would have caused the fuel to be pushed up into the upper cylinder right next to the open exhaust port, almost certainly causing it to either run very badly, or not run at all! If I had to guess at the problem, this would be it.

New screws have now arrived, I’ve put it back together and yesterday afternoon I mounted it on my test stand and gave it a flick, I’m pleased to say the little 2 stroke now runs really nicely, throttle response is smooth, WOT sounds fine and it happily idles at a very low RPM.

Quite pleased then! Just need to find something to build to put it in.