Ah okay, the ones I'm finding on eBay all want 500+ and don't include power valves, coolant pipes, and some even cylinder heads! I'm going to extend the effort into tracking down the one that was supposed to be with this bike...
I was indeed, the other one I was thinking of was the 3BN which apparently has an extra amount of material protruding from the cylinder head which disrupts the combustion flow or something (they called it a combustion ring when I first read it which made me think it was one of the piston rings they were talking about). Very much new to 2 stroke mechanically, I wasn't quite as interested in engineering when I had my 50cc at 16...
Interesting, why is the 4FU considered better? Is this just down to the Nikasil plating in the barrel or are there other advantages?
I wonder whether the cranks are interchangeable between these, i.e. whether just changing the barrel and cylinder head would work...
If I can get the stock engine back I'll be more than happy running it with a fresh rebuild for quite a while, I'll need some time to get used to the 2 stroke powerband anyways
I imagine I'll end up getting a spare engine to start porting/tuning down the line anyhow.
haha thanks mate I appreciate the welcome!
Love your prev bike section on your profile btw...