Jetting for Vespa 200

Hi folks:

I just bought a Polini exhaust for my Vespa 200. I also had my cylinder re-bored to 67,5mm diameter, so now, it´s a vespa 204cc [;)] .

Before this, it had lack of compression and it seemed to have a rich mixture.

I imagine I should now change, at least the main jet, ¿or shouldn`t I?

I would thank any information and/or jetting settings for my configuration.



Vespa racing

the exhaust is already bulit into the bike.

The sound is very metallic; is this the way it has to be?

I started the bike with the regular main jet (116). When the bike is heat-up, I put the choke on and it stalls; can I assure that the mixture is not lean?

Nevertheless, on monday I will put a 120 main jet and start the running in

advices, warnings?



ref pollini exhaust, do u see the 2 mounting brackets at the rear of the pipe where bolts to engine? cut one of them off!!! will let you mount onto the stud easily as it is more flexabile, but still strong enough. make sure it is bolted to the engine!!! or it will break at the down pipe were it joins the chamber within 2 weeks!!!


I am from madrid, and I din´t do any of waht you did!! If you come again, don´t hesitate in contacting me.

I am more „racing style“ than scootering rally.

see you



I guess that in the following cut-out drawing of my carburetor,

the air tube is nr 11 and the atomiser nr 12.

is it right?

by the way, do this parts have some effecto on the fuel consumption?



Original von BEERACE: Just a thought on this one. Why do you think it was running rich, Miguel? Was it running rich always? did you change anything that made it run rich? did you think it was rich because of plug colour? More info required.


My thoughts about being rich were not from the plug colour ( I have heard that with new fuel aditives, „reading“ the plug´s colour is not as good as it was some years ago). I think this because of the „feeling“ of the bike.

When I go at mid-rpm´s and accelerate, the bike first falls and then revs up. Also without the filter, a lot of gas is pored to the outside through the carb.

I think it is rich because of that, but it can also be a lack of compression. I will start with 122 an lowering as well as reading the plug. Mi intention nevertheless is to do the run-up with the 122 (the cylinder is re-bored) and then start carburating. Of course, the run-up will be done with Castrol TTS, I don´t wan to be messing aruond more time with the cylinder.

Thanks for your advices and if you think about anything else. please tell me



the bogging down when you accelorate could be you need to change the atomizer tube.bigget cylinders need a good mist of gas vapour ,a smaller air tube wont atomise the fuel properly til the revs pick up so it bogs down.try a 190 air tube and be5 atomizer,youll be suprised the difference if thats the problem.polini pipes do sound quite tinny because they use cheap quality metal.if youre worried about it being lean with a 116 jet go up to 118 min,better too rich than lean,finally retard your timing to 16 degrees btdc(swing stator plate clockwise till it stops) for a cooler running engine,oh yeh,and the fuel blowing back out the carb with no filter is the back pressure in the crank housing caused by the rotary valve inlet closing interupting the flow of gas so the only way it has to go is out the way it came.has that covered everything for you???

stroud valleys(midnight hour)sc est 1984

MIGUEL. Did I miss you last summer? Where are you in Spain? I did a big tour last June/July. Did the Madrid Scooter rally at Alcala and everywhere from Barcelona (did the Moto GP) Then everywhere from Zaragoza, Valencia, Denia and on down to Murcia. Met many great scooterists and drank lots of BEER. Had an amazing time.

you need to keep off the throttle for 150miles in total miguel.definately for first 100 but then some more gas for last 50.sip have all the bits you want so why waste time.when you get bored of the setup you have go balls out malossi,you’ll love it

stroud valleys(midnight hour)sc est 1984

try a 120 if its a px200 or a 122 if its a p200e as a start but may need one up from that .alternately port the bugger and use a 125/130

stroud valleys(midnight hour)sc est 1984

Just a thought on this one. Why do you think it was running rich, Miguel? Was it running rich always? did you change anything that made it run rich? did you think it was rich because of plug colour? More info required.

3 tanks at a steady pace you need 150 miles of steadily increasing pace.once youve done 100 miles rip the old girl wide open in 1st 2nd 3rd then take it cool in 4th.enjoy!!

stroud valleys(midnight hour)sc est 1984

I have had some problems fitting the polini correctly, nevertheless, my friend Mr Dremmel will help me in my job.

About the carb spares, in this almost-third-world country that is Spain, I haven´t found yet theese dell´orto spares. I will keep on searching and if not, I will bring them from sip. Hope by mid next week everything is running.

Doc, you talk about 100 miles and then 50 miles. Does this mean 150 miles of running in?

or just sweet first 100 miles and a little bit mor strong 50 miles afterwards?




I will try to understand logically everything you told me with the cut-out scheeme of the dell´orto 24 [;)]

Thanks for everything; I will keep on asking and hope you keep on answering my doubts.



Thanks doc!!

loved the burger!!!

i will start my running in; 3 complete tanks is enough? with a rich mixture and with the new air tube and atomiser and then, I will start leaning the mixture checking it with a new spark plug.

I will post pics!!

And I will keep on asking [;)]



thanks stubbsy!!!

I will cut it ASAP, I hadn´t thoug about that and I was going to mild the corners.

once again, thanks for you advice


you got it miguel, 11 and 12 it is.if anything the only effect it can have on fuel consumption is to make it better,although not noticable.because it changes the mixture into a perfectly atomised mist so making it perfectly combustible it can do its job easier and better so the engine wont have to work so hard to process it.its like buying a cheese burger and getting them to put it through a food blender first.its the same burger,no time to chew,easier to swollow and easier to pass out the other end and every mouthful has the same amount of bun,burger,salad and pickles.the first bite isnt all bun or all burger.if the fuel is perfectly mixed with air and atomised finely,the engine doesnt get a squirt of fuel surrounded by a big vortex of air,its all mixed nicely and can displace itself throughout the squish chamber for optimum combustion.hmmmmm fooood now im hungry

stroud valleys(midnight hour)sc est 1984