I got 40 mph on flat with a complete 100$ stock 103, just 2mm exhaust porting.
In my opinion keep your peugeot stock right now, I mean do some research to get the best out of it with mild porting, variator 3 balls, etc.. without spending a dime, especially not in a malossi reed block.. and save your money for when you're ready to do the real upgrade for 50+ mph top speed.
When your ready with the right budget do this:
Spend the money where it counts
Get an er3 variator the best for peugeot, the variator is EVERYTHING on those french bikes
dont be cheap and dont get the er2 you'll regret not buying the er3
locticte the guide threads, grease all the moving parts, maybe add a shim inside so the belt seat almost all the way down to regain a little low end
get the malossi belt little wider and little more range than the doppler belt
(moby get the doppler belt)
keep ur stock clutch system
might need a 2nd clutch trust washer with 70cc kit that runs hotter and makes the clutch sticks at idle sometimes
keep ur stock crank
keep ur stock cases
Get a gila 70cc kits for easy case port match (dont port the kit)
(it's hard to make a peugeot 50cc rip, 70cc rips out of the box but keep it low rev, reliable, you'll be happier with the torque than with a 50cc kit, moby 50cc kits are toruqy and rips because of the ports and different stroke
get a malossi reed block
get a 17 or 19mm carb (clamp style cause not much room with sub frame, 15 or 16 will run if you worry about gas mileage but won't be as powerful
cut some of the sub frame to create room for ur carb and filter, dont be afraid it won't break
get a good high comp no decompressor head 70cc like polini and plug both decopmp holes the big and the tiny one.
peugeot head gasket always leaks there no matter what when is gets hot especially with 70cc kits, air always gets suck out.
also tap and plug the decomp hole in the cylinder with 1/4" allen socket screw, should be tight and bottom out almost all the way down to the exhaust port wall
use a malossi 70cc aluminum gasket + rtv red silicone on both side
(always check for leaks though with peugeot kits hot due to small air fins, and re-tighten the head if needed or change the gasket)
get a motobecane stock cdi at treats (easy conversion for peugeot, may need 2 spacers between the stator plate and grind 3 spots to clear the cases bolts) dont get the gold tapper stock cdi version from 77mopeds the trigger mark to set the timing is off.
there's NO perfect spring on the market = cheap, right tension and good quality
lose ur stock spring and get a doppler spring, little expensive but better quality than polini aluminum mounts that breaks or falls off and spring too soft needs to be combined with stock one.
find a way to replace the ball joint type nut that tends to come off the bracket making the spring lose and potentially losing it when riding or removing the belt, with a rod end ball joint + screw through the sub frame, much safer.
doppler spring a little too strong sometimes for low revving engines that needs all stack of weights on the variator to be tuned for take off and top end. If you struggle tuning it you can always go to a spring store and replace the strong red doppler spring with softer smaller gauge one.
pipe I would say doppler for good all around power and top speed but u'll lose the pedals
if you have the money get the new polini pipe good mid top end, should clear the pedals
less budget get the simo circuit pipe low mid range but it often cracks with peugeot vibrations, gotta be rubber mounted but sill no guaranty to last
I think that's it.
you'll be very happy with that set up with 50 mph guarantied that should be reliable, but I don't know lots of fast peugeots reliable blasting everyday :)
there's always some little things going wrong that you gotta keep an eye on, lose pipe ball joint if you didn't secure it with extra bracket, cracked pipe, lose baffle, clutch disc broken (especially after market ones china), head air leaks, I guess common stuff on kitted mopeds in general but more on peugeot because of the vibrations (no rubber bushings), swing engine, and super tiny cylinder fins.