Modern Vespa

I recently bought a Zip as bit of a project. Previous owner said it got hard to start then wouldn't start at all.
After cleaning the carby, checking air filter and changing plug I could get it to start with throttle and run but then it would cut out after about 5 minutes and not start again.
Now I have put a secondhand carb on and cleaned it but despite multiple adjustment's and tinkering with the air mixture and idle screw it will start and run fine on the stand but die at load on full acceleration or going up a hill.
It seems to run best with the air mixture screw only about 3/4 turn out whereas most say around 1.5 times out is about right.
Probably worth noting it has a malossi air filter in it too which may be relevant?
I am starting to lean towards an air leak as the problem and wondering if there might be potential issues with the inline vacuum filter which is in the air hose running from the fuel tap to the carb?
Wondering if its ok to run the scooter with a new vacuum hose and without the filter as a trial as I am not really sure how important/useful that filter is?

The vacuum line as you call it is what turns on the fuel flow so if it has a decent leak....no fuel. Which maybe why it doesn't start.

The vacuum line shouldn't have a filter on it. I have seen ones with an inline filter on the fuel line (although there is already one on the petcock).
Replace the vacuum line and see if that helps.
Mixture screw 3/4 turn out, if everything is attached properly and the inlet manifold doesn't have any cracks, I wouldn't worry about it. My et2 is set to around 1 turn out and runs fine.
I'm assuming your filter is a direct replacement and still uses the air box and you have oiled it.

Thanks for your reply. Definitely a filter on the air line and you can buy replacements but not really sure if they are necessary.
No shops open here today but will buy some vacuum hose and give it a try in the next few days.
I have already replaced the manifold inlet but the air filter may be an issue as I don't think it is stock and it certainly isn't oiled.

Buy a can of Starting Fluid. If it fires on that then the problem is not electrical.

I was given a Chinese 50cc two-stroke that would not run. Turned out a mud wasp had built a nest in the silencer/muffler. I discovered it after I disconnected the exhaust and it ran fine.

Thanks. It definitely fires on starter fluid.
Hadn't thought about the possible muffler issue but its another option I will check out.

Update. I have put the bigger main jet (65) from the old carb and the air gauger from the replacement carby (see photo). into the replacement carb and it runs fine now but the air mixture screw is still only about 1 turn out.
I assume the bigger main jet is required to match the malossi pink air filter.
Only problem now is that the scooter is very hard to start when cold.
After several attempts it seems to chug over and finally keep going and then its as if the auto choke kicks in and it revs really high then dies down to normal as it should.
After that it will start and run fine but cold starts are a problem.
Any ideas on this one?

Problem solved. It turns out that the older style Dellorto PHVA Carb which I put on the scooter has a choke jet in the carb bowl. So I had previously cleaned all the carb side jets and the bowl but didn't know there is a small jet for the choke embedded in the carb bowl. Once I cleared the tiny hole in that its starts first go and just needs a little tuning now. Hopefully this is helpful for someone else in the future.

Good catch! That one is a gotcha on old Honda 2T 50s as well.

I think I have a similar problem, are you saying to remove the vacuum filter entirely?

It started with easy start sprayed down the spark plug hole, but otherwise won't.
I'm can't find any info about what it does?
This is filter, I've replaced the fuel line since this photo

I took my vacuum filter off all together and it didn't seem to affect it at all. Once I cleaned the little jet which is inside the carb bowl on the older models it runs well and I haven't put the vacuum filter back on.

I am still having issues, have read a lot of how to guides, and threads but am now stuck.

Symptom: Stood for 5 years, and would not start

Vespa 50s, with PHVA carb

Work so far:

Replaced ignition switch.

Brand new battery which I keep charging after all the false starts.

Replaced fuel and vacuum lines
Striped carb and cleaned it, replaced:
Main jet
Idle Jet
Bowl gasket
Float and needle jet

Petcock was old and not working, so I replaced with cheap one, which leaked and did not operate correctly. Now on second one, different make, which definitely works and pulls fuel from carb when attempt is made to start.

Flushed petrol tank, new E5 fuel

Replace in line vacuum filter, have tried it with and without that

Original E choke not working, tried an aftermarket one, but didn't seem to do anything, so tried a manual choke, which I have switched back and forth.

It has started, but revved very high and I think it was because the throttle cable was not installed correctly on top of carb. Have corrected that, still wont start.

I have tried fiddling with mixture screw, 2 - 3 turns out, and idle screw too.

Any ideas?

Hi guys
I always read articles / comments of people simply removing their carb and cleaning etc. I have pulled all the plastic off mine and still find it daunting. Is it that easy? Did you remove the carb and completely clean each and every part of it?
So far, I am the same in that I can only get mine to start with starter spray.
Thanks in advance

There should be some useful you tube videos about cleaning carbs. You just need to remove the carb and apart from general spraying with carb cleaner you need to specifically focus on cleaning the small brass jets which are usually the source of the problem.