Modern Vespa

because the fuel feed is gravity fed driven there will be ALWAYS a pressure difference following from the height of fuel weighing down on the tap opening.
The only solution to a constant pressure is an electric fuel pump.

There is a breather hole above the float chamber. When you turn the carb upside down, this is where the fuel runs out from.

You quite right. Absolutely "d'oh" moment. Yesterday I take off carb for cleaning. All was clean inside only very little dirt on the filter.
But...
Here you is little bastrard.

Interesting that when I cleaned carb two times before there was nothing. I went to work today on PK and almost everything was fine.

This problem remains, but now it is not very noticeably - now it appears after 800-1000 m on WOT. I'm absolutely can live with it because I very rarely ride PK in the city on such high speeds.
But I will try to shorten fuel hose because it have loop than I don't like and next step will be change fuel tap.

Normally thing kind of thing is a hair or piece of plastic but that will do.

For the other issue are you sure the main jet is big enough? Works like rough or jerky are often used when talking about lean jetting.

It's impossible to tell from your picture, but is there any point where there's and overhand loop and you could get an air bubble?

Thanks. I will try bigger main jet. Thats what I'm thinking about. It seems that there is place where loop on hose is higher than fuel tap on the tank.

So. New season - old problem.

Today I changed fuel tap, float, needle for one without spring, re-routed fuel hose.

And following Jack221 advice changed main jet for bigger(108 to 115). 115 MJ is too rich. Rides terribly, can't even reach 50 km/h.

So I put in 110 MJ and will test it tomorrow.

Tried with 110 MJ. For sure better than 115, but still rich.
Problem also still present. It seems that 108 MJ is perfect.

It never starts from first kick - two, three or four. Engine works unstable, sometimes feels like spark missing(?). After it gets hot - all turns better. It holds on idle without problems.

Here also video of cold start, after night sitting in garage.

watching the cold start video, seems like you get little to no throttle response when you try to blip it. Towards the end, there was a sag, like it was maybe lean?

I'm going to randomly guess that the idle jet is partially clogged based on that. Very low confidence, but it's an easy enough thing to check.

chandlerman I checked all few times, cleaned carb and jets few times also tried different jets. On video is 52 idle jet and yes it seems bit lean, with 55 I liked it more.
But overall picture of cold start is the same, no matter 52 or 55 idle.

I'm absolutely exhausted with it.
I have two last ideas to check. I will change ignition and if it will not help I will put in other carb(19.19).

It might be that the blockage is in the idle circuit, rather than the jet, and the carb needs a more serious cleaning, maybe an overnight soak in carb dib followed by a really good blow-out, given that changing the jet jet doesn't seem to matter.

I seriously doubt it's the ignition.

Those failures mostly happen if 1) the engine is warmed up (CDI fails); or 2) You're me.

Carb is new. Few thousands of km.
And on previous cylinder it have no problems.
I soaked it and blowed with compressor few times.
Changing the idle jet don't affects on cold start. But it is noticeable - with leaner idle jet the idle is higher(mix screw not touched)
All passages in carb is clear.

agreed. Passages all look clean. Nice macro lens, too

Just iphone 12, captured then zoomed and cropped

108 seems like it's the jet. You try 105? Often two jets between splutter and done.

Agree with lean for the pilot. How you adjusting the mixture screw? Could just be that.

Jack221 I'm not tried 105, but I will also try 107 and then 105. Anyway 108 seems perfect.
About mix screw - on the warm engine I set it so that engine will go back quick to the idle after throttle blipping. With the 55 idle jet it was 3 or 3.5 turns out. Now I think that it is too much, and 55 IJ is lean.

Today I put 109 MJ and 58 IJ.
109 is still bit rich(as I mentioned few times above - 108 is much better if not the perfect)
58 seems more or less ok.

But the problem with "lack of fuel"(how I call it) still present.

Is the idle jet affects the main jet on the WOT?

Everything affects everything in carbs, question is how much. Jets flow by area, so 3 points on a pilot jet might be not even 0.25 point on a main jet. Even if it was that simple, most carbs pilot jets flow progressively less as the slide opens, more than a quarter. In summary, you think it should but makes little difference.

Try setting the mixture screw by opening the screw fully, at least 4 turns.
Increase the idle screw almost fully. If the pilot jet is close, it should be sitting at less than 1800rpm. Close the mixture screw until is suddenly speeds up. This will be somewhere near. Slow the idle to under 2000 and adjust the mixture out to the fastest speed.
How do the turns compare to the blipping it method?

Great advices as always, Jack221. Thank you. I hope I will have time for it on weekend. Vespa also have no tacho, but I have laser one, and will test it.

After good WOT run spark plug was absolutely black. 109 MJ and 58 IJ, mix 3 1/4 out.
Also it was impossible to reach 90+ km/h where "problem of lack of fuel" appears.

I'm still inclined that 108 and 55 was perfect if not count the "fuel problem". Spark plug color was perfect too.

And I'm still thinking the problem is in ignition or in whole carb.

Just put in 107 MJ and will try it tomorrow.

New day - new symptoms.

All was ok in the morning. Starts from second kick. 15 km ride to work was nice.

Then rain starts, Vespa was outside but under the roof. It even wasn't almost get wet. After 8 hours it starts very bad. Lot of kicks but then seems ok.
Warm it for few minutes and go home.

After maybe 500 meters it starts to bogging hard even with WOT, engine works very unstable and then died.
Spark was ok and then new spark plug was in. Nothing changed - spark was ok on both spark plugs.
After lot of kicks it starts for few seconds and dies. With WOT it dies even quicker. Then all repeat: lot of kicks and few seconds alive.

Sometimes it shoots or sneeze into exhaust really hard and loud. Playing with mix screw made not big difference. Dancing with for maybe 15-20 minutes and it suddenly starts and idle. Very bad throttle response but still idle.
I fully turn in idle screw and after few minutes it idle somehow and I turn idle screw back. It works. Ride home and near the garage it sneeze again in the exhaust and died.

It turn me mad.

Definitely female. But more clues as to how she's feeling.
Electrics or pressure test. I'd go with seal leak first.

I thought "electrical" from this: unless something got lost in translation.

broken stator plate, maybe?

Thank you Jack.
I need to learn more about leak testing.
On the other side - engine is dry and more or less clean everywhere. Flywheel side crankshaft seal is dry too. And gearbox oil has no even a hint of the smell of petrol. My bad.
"Spark was ok with both spark plugs. But nothing changed about engine starting" .

Finally Snowball is on the road again.
The problem was in bad ignition.
First I ordered new "original Piaggio" stator plate, Grade 1 - faithful restoration.
And it was defective. There was a spark but engine won't start, shooting hard and loud into exhaust, misfires very hard.
I messaged to SIP and they put some money on my SIP account so I order another stator plate. This time it was RMS part. And all turns good. After two months sitting engine start from 3rd kick! Done short ride to the tire shop today and all was nice.



Original part




Also gave it a really good wash.

What do you guys think - what did I do? Yes, I bought another PK 50 S.

The previous owner wanted to sell it for metal recycling. And when I saw the photo I couldn't pass it up, especially since the price was symbolic.

Yes - terrible condition, crankcase even have no any studs that holds halves together, some other parts is missed...
On the other side it have nice original 125cc speedo, dashboard lamps is in better shape than on the Snowball, original model correct seat(but new cover is needed), etc...

I don't know what it fate is yet, but it's definitely better than being recycled.

The photo I'd got from owner and thought "oh another poor rusty and abandoned Vespa without papers and in unknown condition? YES!! I. NEED. IT."



Traditional photo:


Got it - 1982 PK 50 S:









I already steal tail light lens for the Snowball - it is in better shape than it current one. And I like this SIEM lettering. BTW front indicators also have same lettering and it is pity that one is broken.


CEV lens what was on the Snowball.

$1 for the reflector, 1 hour for good cleaning, few days soaking in silicone and Stilmotor rear bumper is back to life.

I didn't know this is possible... 🤔 Please do elaborate, for the uninitiated.

Rikko nothing special here. Old plastic parts can be refreshed with cheapest silicone oil.
I'm using silicone spray. Give it good clean, degrease and good spray of silicone and left it overnight or two, or three. Then wipe out silicone with clean cloth.

I never used but I'm sure that special dedicated plastic conditioners and renovators will give even better result than silicone spray.

This autumn come so fast and hard. Very cold and rainy almost the month...

On red PK 50 S there was original seat. Ripped and rusty. I'm thinking a lot what to do with it and decide to give it for renovation.

It was sandblasted, powder coated, new cover and filler was made. Seat belt remain old one.
The main idea was to got close to original look. I even want left original rear panel with Piaggio lettering but the material turned out to be too old and fragile. So I decide to put there original badge from my P 150 X seat. Of course I will also give it attention later. I also put new lock cylinder.

Now the Snowball have model-correct original(almost) seat.

Finally I got sticker for seat badge. I like the look.

That seat came out great! 👍🏻👍🏻👍🏻

Suddenly speedo start to show +20-25 km/h from the real speed. Needle don't jumping, it moving smooth as always...
So I borrowed speedo from the Red Rat. Very pity as it looks worse, also needle is crooked and don't seems like it will last long.
I'm absolutely don't like new repro items... I don't understand why they can't make a 99% similar speedometer? Well, okay, maybe without the Piaggio emblem and/or the inscription "Veglia Borletti"...
On the other side $160 is too much for me for the original NOS speedo

Maybe you can get a new repro speedo and transfer the faceplate? Or sometimes opening the speedo and greasing the 43 year-old internals can help.

That stilmotor mudflap is pretty cool. Stilmotor made some questionable accessories for vespas, but I still like the thought that went into some of the stuff they made.

I am guessing that needle return spring is at fault, assuming everything from the wheel up the cable is ok.

Good idea! I'm not even thinking about it!

The Snowball in the snow.

Any driving vids?

No mate. Circumstances force me to use scooter for commuting to work and on business. So I have neither the time nor the desire to set up the GoPro.
I didn't even have much desire to just take a photo.
I already done near 700km of this daily riding. OFC not all 700 in so hard snow but also not in very pleasant weather conditions. The biggest problem is the cold, quite often down to -10...12º C.

Yikes!!! When it's like this it's less fun. I do commend you nonetheless.