[jonathan150cc]

Usually, there are 3 main points of restriction.

On the variator bearing, they install a little metal washer that won't allow the variator to slide all the way into top gear. This, of course, limits your attainable top speed. They do this because most 50cc scoots are supposed to be limited to 35mph. Once you slide the variator off, this ring will just come off with a little force.

Also, the stock CDI is programmed to limit revs. Most of them can easily be tricked into simply not limiting revs by unclipping one of the wires. Or, you can simply replace the CDI with a non rev-limiting kind. Those aren't very expensive, if you go that route.

Finally, they have two ways of restricting the exhaust. They either tap weld a small diameter washer inside the exhaust right up near the head. These washers, or plugs, can simply be drilled out. I've also seen these strange pig tail devices which look like a second head pipe coming off the main pipe except that they are closed off. You saw those pig tails off but you'll have to find someway to seal off the place where it was attached. Most people just weld over the hole.

You don't have to change carbs. They are pretty spunky in stock forum. My sister-in-law just got one a couple of weeks ago. I've been pretty impressed with it. Total cost, shipped, was $854. I do plan on removing the autochoke. These are nothing more than a big black plastic fuel waster. They enrich the circuit when the engine is "cold" and they sometimes don't turn off, causing you to run way too rich for way too long. The autochoke on my 150 was removed and I've never had a problem starting my bike, warm or cold. Removing that will undoubtedly save fuel. And, combined with the other things I've mentioned, you can get a pretty good top speed right out of the box. She's on 87 miles right now and it looks like she still has a 1/4 tank. These things only hold like 1.1 gallons. So her mileage is looking pretty good.