Bruce

Well, I got to the bottom of it, for those interested Turned out to be a pin hole sized leak on the inlet manifold! Took it off, cleaned it, loads of silicon, torqued it down. Sorted!

My grandsons ST125 has developed what I can only describe as a squeak! The last week has been a bit of an adventure. While out practicing last Friday (16-09.20) the bike, for absolutely no reason revved its head off. It did this once before 3-4 months ago, but was fine after, and couldn't find any reason for it. Well this time, when the bike was restarted it rattled badly. so straight back to the workshop and off with the head and barrel. There didn't seem to be any play in the little end, and the barrel looked OK. But the piston looked completely knackered. So I replaced Piston, Rings, Gudgeon, Little end bearing and gaskets. Upon rebuilding, the engine sounds a little bit rumbly (but that could just be me being overly critical) but it has a squeak! similar the noise a 4 stroke makes if a valve seat is blowing. except it goes away when revved, buy comes back when the engine returns to idle. I have tried bunging the exhaust to see if that is blowing, but (odd in its own right) this has no effect, doesn't even load the engine at all. So I've checked the exhaust for leaks, NO. I've sprayed the inlet with WD40 to see if its drawing air, nothing! So I'm now at a loss! does anyone have any ideas? TIA Bruce