dur u guys are all derb and hobbit crazy right now. I'll break it down
your number one choice should be peugeot 103
why? cuz its easy to find, parts are plentiful, you don't need to swap many motor parts, and it responds very well to minimal upgrades .ect to make it fast, its easy to step up slowly and easy to work on. also there is a variator and a chain so lots of gearing. the only downside really is the swinging motor if its really a downside, anyone who tells ya a french bike can't match a derbi or hobbit 4 performance doesn't know what they are talking about its just a bit more work to get the uber power outta them.
that being said if you can hold out for a derbi if you are truly looking for the max and getting it with alot of bolt on tech. they are also easy to work on and respond very very well to minimal upgrades. all the models even piston port can go fast, also these bikes are by far the beefiest sturdiest of the choices. but are very rare and parts are also not as plentiful. also like the peugeot it has a variator and a chain, so there is more possibility for gearing. on the plus the motor does not move.
3rd choice hobbit, similar to derbi in many ways stationary motor counterclutch system, however there is no chain drive so all the gearing is internal, meaning more work to change if you desire. the shittiest part about hondas if you have to literally take the whole bike apart to get to the carb, not to hard if your used to it but really shitty if your tuning a super setup. these bikes are also quite rare but no as much as the derbi. Also unless its squeeky clean these bikes run crappy with stock carbs, really crappy cuz it clogs daily.
4th choice is motobecane, almost identical to peugeot in many ways except in the details, motor mounted by he head, crappier electrical that's harder to swap out, comes with a piston port motor and the real power in is the reed av10 euro version so that needs to be swapped for max power, the whole bike in general is much more delicate then the other options and should be treated such. its the easiest bike to access all the parts making it fast to work on once you know the ins and outs. I won't get into all the details that make it the 4th choice but there are alot of small hurdles and $$ to get over b4 you can make one epic fast. thus they don't respond well to minimal upgrades.
lastly the vespa is something you want to steer clear of unless your out looking for a challenge. these bikes have just as much (or more) potential as all the others but the amount of work involved to get there eclipses the other choice 5 times over. the main downside being the stock case intake is not a true rotary valve and has a stock intake port of 13mm that can't be increased really, and most kits (all sold by us moped distributors) have tiny little exhaust ports because the motor has a 3 stud cylinder design and the 3rd one is right where the exhaust port should be, so there is a tiny port even on kits. Meaning it responds poorly to minimal upgrades and super setups are also hard to achieve. the variators are also smaller then those on the derb and honda, and there is no chain drive so its also all internal gearing. There are many more details that make vespa super hard to sup up, but the last and most lame is the fact that you have to drop the motor and basically disassemble it to get to the ignition, hella hard to do if your trouble shooting a cdi or something....like i said want a challenge go vespa otherwise don't touch it.
all other variated bikes are too unsupported to really include in the list, but if you resourceful anything is possible.
Also as others have suggested like honda motors on moby etc. anything is a possibility, and any of the bikes can be made into the masterblaster no mattter what the make/model check it:
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