what does putting a fatty on a 4 stroke do? anything? is there a way to make one work on a four stroke?
Dude, what are you talking about? What is a ‘fatty’? Never heard of it.
I’ve been tinkering with mechanicals all of my life and I also have no idea what a fatty is.
Is it an overweight girlfriend or a type of large chambered muffler; possibly from a 2 stroke?
Neither one is going to aid performance though. 
It’s a pipe they put on 2-strokes, and no, there’s nothing good that would come from putting one on a 4 stroke bike. I don’t know enough to be specific, but the reason for the chamber on a 2-stroke bike is the fact that they have an exhaust event every other stroke.
yes, it is an expansion chamber in an exhaust pipe on 2 stroke dirtbikes. creates a vaccum and pushes air into the cylinders much like a turbo, this is the reason 2 strokes have huge powerbands.
No, in fact it would be detrimental to a four stroke bike’s performance. Think of it as a cause for greatly increased back pressure. That’s how the engine would see it.
It’s been a while since I studied this. I welcome corrections for errors or omissions, but here’s how I remember it:
The opening of the exhaust valve creates a shock wave in the exhaust pipe. That wave ‘bounces’ back and forth in the pipe causing some amount of interference for the main volume of gases trying to exit the pipe. A “tuned exhaust” is designed to have all those shock waves primarily aligned to be rushing toward the exit of the exhaust at a certain RPM range. The synchronizing of the shock waves will help to ‘pull out’ or ‘scavenge’ the exhaust from an opening exhaust valve - creating opportunity for a denser intake mixture.
The OP asks if it will work on a 4 stroke. Yes, but I’m not in the industry enough to know how much of a noticeable difference it will make. I’m sure bike manufactures already do some tuning on their exhaust systems for their performance 4 stroke bikes. Someone in the trade will need to comment on whether the after-market exhaust systems will outperform the factory exhaust on the performance 4-stroke bikes.
well i dont know how your girlfriend would react to being called a fatty. JUST KIDDING EVERYBODY GET OVER IT. you should find a forum for your bike or quad, it would surely make a difference but might not be wrere u want it.
i did, its called dirtrider.net, it sucks, people are smart alecks there noone will answer your question