50 Special Tuning

Im thinking about tuning my 50 special. Can anyone give me some suggestions for 115ccm kit. Best value for $$$. What are the best combinations, cylinder, carb, crank, reed valve, exhaust?



Realistically you have no chance,epecially if they're tweaked.However,I digress.

I've looked around and SIP don't stock full circle cranks for a 43 mm stroke motor so you've 2 options,either stay rotary or go with a 51 mm crank.The former will be cheaper.It's your choice.

I'd use these.






Remenber to get new bearings,seals,gaskets and an uprated clutch too.

Hi to all,
actually i found out that my engine is an original 1967 Vespa 50S 50 cc .
Already changed carburetor to Polini 19mm, exaust - Polini raicing.

Aiming for a Polini 115cc Kit - is it a right choice or to powerful for my engine?

The kit 130 Polini is very good! If you want to go fast it's th better! But you have to change the clutch!



OK. Link does not work, It`s a Polini 19mm carb kit.



Your vespa shouldn't overheat in your current configuration. Many times things are not done correctly. First of all a lot of kit are mounted like that without ever checking the ignition timing. Other times you find not the correct spark plug heat range. Other times is the carb. that has not been set up and just left as come from the box.

If a 75 is well set up would not overheat even in climbing hill all day.

To get more power and torque you can go to a 102, (112 are more delicate).

With a 19mm carb. set up right, ignition set up right and a gearing ratio of about 3.00 you have a nice climbing machine.

If you can spend more you can go with a 130 kit.

All these kit has proven to be extremely reliable over the years and if you have any problem is not the fault of any of the "classic" kit, but they come from a approximative fitting.

good luck




In my opinion, if you do the following, your firends with modern scooters would see just your backlight :-)

130cc polini racing GT

Shaft 51mm mazzucchelli AMT160 (compared to the standard 43mm V50 shaft, you gain a lot of torque!)

27/69 gear box

carburator 19:19 with Polini Filter (nicer would be 24:24 carburator but carburation is trickier to adjust, it obviously consumes more and you need to rework the carter to match the bigger carburator manifold)

Faco "banana" exhaust"

you need to have also better clutch (minimum the reinforced spring and good quality clutch disks)

Probably more acceleration than top speed. Something to come close to new age scooters. 



I was thinking pretty much the same actualy, the only difference would be the carb.

I would take polini because it`s got reed valve included.


I`ll keep you posted, what I`ve decided to do.



how to tune Vespa 50cc (75cc kit) to real world performance ( less overheathing) rather than the top speed?



Before we get into this,what are you aiming for?Top speed or real world performance?

Reed valve won’t work without a full circle crank,stick with a rotary set up.