Ok because we are all a bit lazy I extracted the interesting part about the difference between a 40cc and 49cc engine (which are usually all misleadingly advertised as 47cc). I just want to say this information is from
http://bcpocketbikeracing.cait is not mine!
I thought others with custom home made project with similar engines would might find this info useful.
How To Figure Out Which Engine Is In Your Pocket Bike
How can you tell if your pocket bike has the 40cc or the 49cc engine in it?
Well there's 2 ways to tell:
1. By Looking
The first way to tell is to look at the 4 fins on the bottom of the cylinder
head. The bottom 4 cooling fins on the 40cc engine join right the way
around the cylinder head, with no break in between them. Whereas the
bottom 4 cooling fins on the 49cc engine stop at the corners and don’t go
all the way round.
Take a look at the picture of both the Cylinder heads below:
The cylinder head on the left is the 40cc engine - look where I’ve circled
the bottom 4 fins, you can see they are joined all the way round the
cylinder. The cylinder head on the right is the 49cc engine - look where
2. By Measuring
etc...