Modern Vespa

Hi just registered

having starting issues with my year 2000 et4 125
once running it's good no misfiring or fueling probs. but
have changed the coil, spark plug, stripped the carb removed bits of crud
reassembled put an in line fuel filter in , renewed fuel & vacuum lines , fuel tap..
checked valve clearances & cam timing , spins over great good spark , but not starting.. thinking it's fuel as with a small squirt of easy start she will reluctantly start , doing my head in as bought to commute to work on , sorry for long post
probably going to be something daft but ..
getting bored of taking apart the cv Keihin carb , & raising/lowering the needle

Once it's running spray around the carburetor with WD-40, or the UK equivalent. It might be a cracked of loose manifold. If the engine picks up speed or changes somehow you will have found the problem. Also, and excuse me for stating the obvious, see if you hear a hissing noise somewhere that indicates a vacuum leak.

Once it starts does it stay running? ..if not, its your fuel tap or float..sounds like you replaced the tap

if it stays running then ..i am wondering about the pilot jet...or if it has an autochoke that might be sticking...

take that pilot jet out and be sure its clean...hold it up to the sunlight and be sure you can see clearly thru it....i use a nylon bristle from a small brush and ream the jets with it....its possible that you need a slightly larger pilot jet in there.....its that or that choke isnt working right

thank you for your replies..

yes tried wd40 on the inlet manifold before no luck unfortunatly.

did strip out the pilot jet , ( & the rest of the carb too) that was where i found some bits of plastic , cleaned it all out and blew through the pilot jet , & the carb body as well

good point with the auto choke will check that as it's electric resistance type.

when i bought it had a 104 main jet in with a cone filter & wrong plug
plug was very rich .
i returned it to standard jet 82 , then put on a standard airbox & intake
put the needle to the middle grove & a standard plug
trying to use the standard settings as a datum to get it running correctly
as it's a ZAPM19000 seems it's an early version of the et4
so carb bits seem less available ?

wondering if the float level is set too low
maybe preventing starting ? , would it run enough vacum to keep running when it does start , or am i barking up the wrong tree ?

it really sounds like it might be a choke issue...the choke is supposed to add more fuel into the carb when its cold to aid with starting...its either that or a pilot jet thats way too small...i have my money on the choke....


i had to connect a manual choke to mine to test when i had this issue

I'd check the auto-choke hadn't seized shut. It's not a common mode of failure, they usually go open-circuit, so the mixture remains starting-rich, which is very easy to diagnose!

Just take it out and test across a battery. If it closes (extends needle) and opens again when it cools then it's OK.

Good luck hunting this down!

thanks i will give ita look when i am off shift , thanks for the input

Welcome to Modern Vespa.

Thank you for all the help
Thank you for the welcome too
I think i have it sorted at last
I took the electric choke off & connected it direct to the battery perfect
BUT it won't work connected to the plug on the loom...
ah ha , two plugs next to each other one male one female
the aftermarket choke it has fitted has the wrong plug , so it was plugged into
the other plug

because it was set up so rich with the wrong jet etc. when i bought it
it must have started off the over rich mixture

always helpfull to have other brains to help solve problems
cheers great forum
Thank you

This is a good find.

I might be wrong, but I would think a disconnected choke would lead to running problems (too rich because the because the choke would never close). But you said you have starting problems, with running being fine.

So if I understand correctly, you are thinking the starting problems are actually from incorrect jetting? And the jetting was setup incorrectly because of the autochoke problem?

it's been a long & winding road to be honest Berto

no it was originaly over jetted running a conical filter cheapo thing
the wrong plug & plenty of neglect thrown in too I was trying to get it back
to standard looking for commuting rather than tunning for speed
I bought it for £100 , just as a fixer up , to get to work on
I have stripped the carb several times found bits of plastic crud etc. in it
adjusted float hight put an inline fuel filter in ,renewed fuel lines , fuel tap, vacumm lines , checked valve clearances timing etc.
replaced the duff battery which was struggling to turn it over
changed jets , needle hights , plug, coil, gone down the rabbit hole with the carb
but like all things you get annoyed , but enjoy the challenge & when you get there in the end , it's a feeling of acheivment