@randomshenans rather than clog up the youtube thread, I'll respond in here.
First off, you'll need to remove any restrictors. The most common ones will be in the exhaust and will be one of two types, a false breather which looks like this piece of dead pipe on this photo:
As per the photo, you'll need to cut it off and weld it shut. We used to just cut them off a few cm away from where it Ts of the exhaust and hammer it shut, we never kept stock exhausts for long anyway. The next one will be in the actual "header" (or flange rather) which could be a washer welded in to restrict airflow. This could be in the mouth of the exhaust, or the flange bit in the photo above.
After that you need to look for restrictors in the inlet manifold, carb and airbox itself. You're basically looking for a big hole which has been intentionally made smaller. Here are a few examples:
That'll allow the engine to operate as it was intended. The next step will be to open up the CVT and look for a washer in the variomatic part (the front part of the transmission). These transmissions work by sliding up and down the crankshaft, an action which is often restricted by inserting a little ring to prevent it sliding too far. Removing it looks a bit like this:
Crack on with that first, going by the sound in the video you posted it's very clearly restricted somewhere, or it has a teeny tiny little carb which doesn't feed the engine nearly enough juice. Get loads of photos of the carb and engine and I'll see what your options are. Start off by determining the size of the carb, it'll be written in mm somewhere on it
