Modern Vespa

can anyone help ? i have just bought a vespa px 200 1983 , it dosnt run in 3rd gear 1st and 2nd and 4th are fine but in third gear at low revs it starts juttering and cutting out ive already paid 2 different mecanics to fix it and no luck ,, it has been sugested to change the jet ,, any other help would be greatly taken

Welcome to MV. You should ask a moderator to move your query to the NSM (Not So Modern) section. You'll get better responses there.

Is it 'Juddering' (like its cutting in & out.) if so it could be jetting.

Is it only when under load? (coil or stator etc.) If you think it could be electrical start with the spark plug 1st.

Or is it 'lerching'(slipping in and out of gear.) poss. worn crusiform.

yes its juttering like its cutting out,, sounds like you describe jetting ,, how can this be fixed,, if i need a new jet wot size do i need as ive been told its a 120 i should put in but someone else says the origanal size is 116 ?

If it does this at high revs, then you almost certaintly need to replace your shift cros.

no its only at low revs

120 should be fine if you've got a non-standard pipe on it.
118 with std. pipe.

Moved to Not So Modern Forum.

Has the scoot been running ok with the current set-up on, or is it a fault that's developed since you bought it?

You should be able to judge your jetting by spark plug colour. If it's black and oily you're running too rich and you should reduce you main jet, if its normal i.e. a tan colour you should look at your wiring...

Is the earth wire from your CDI connected to your engine casing? as this will cause poor running at higher speeds which aren't noticeable at the lower end - it's not uncommon for these to be snipped off for some reason!

Likewise you may have a faulty HT lead, cap or even the CDI, so try replacing these as they're fairly inexpensive.

After that it may be worth checking the resistance values of your stator (Haynes manual will tell you how).

ive only owned the scoot for 6 weeks and so far ive only been able to go out on it 3 times ,, at first it wouldnt keep running when you slowed down and sometimes seemed as if it had no fuel but when it was running it went great , i then left it in to a scooter mecanic who gave it a service unfortunatly one day later it went back to doing the same thing,, i left it in to another mecanic who cleaned out the carb , after another quick spin it now idles fine but i noticed in 3rd gear it was shuddering and sounded like it was trying to rev itself and cut out,, i have just checked the main jet and its a standard 118 so that seems fine ,, should i try a new jet or should i give up and buy a car lol only joking

Try going for a ride with the fuel cap off, it could just be an air lock.
If this cures it drill a bigger hole though the cap.

Check that theres no air bubbles in the fuel line.

Then its on to the carb.
Clean the carb & the jets, (with an air line if you've got one.)

It's just going to be trail & error really.

+1

could be a fueling issue - breather hole blocked etc. Definitely recommend getting yourself a haynes manual tho. There's no need to change the jet as these don't wear at all and if your scoot's standard then you should be reet on that front. If you can't be arsed checking the stator etc. just try swapping them with someone who has a (working) PX. Unless your mechanic was particularly familiar with geared vespa's all they tend to do is change your oil and clean you carb when you ask them to do a service so you might as well just try and sort it yourself - cheaper and at least you know if something's been done or not!