Modern Vespa

I noticed that leaking appeared on the stud and to the ignition area.
I knew about the possible weak spot but hoped for the best. So 10-12K km later it finally happened.

Engine again on the table.

I noticed lot of play in primary basket. So I took my old DRT Cobra primary and used it as repair kit.


I need to enlarge springs pockets for 1 mm from each side - SIP springs is longer than DRT ones.


And grinded down springs ends so them fit proper.


No any play now.

One good guy gave me his old XL2 clutch. I decide to put it on.
Not an easy game but in the end I won.
DRT clutch plates stack is too high and springs is compressed fully, the clutch don't work. I decide to use 3 three DRT corks and two standard steels.
Now all my four Vespas have nice and soft clutch levers.

Finally received the XL2 clutch cover and spent few hours with dry building and adjusting here and there.



Cover requires 1mm spacer. Happy that I have one in the spares.


And file a bit on the brake plate.


I also need to change the spring as new one jump out from the slot when lever is engaged.


In the end all works very smooth and soft.


It will be nice if Malossi springs will hold the power(no luck with my other PK with 144cc) because it will be super to have such soft clutch on the daily scooter.

Despite SIP states "Grade 2" for this clutch cover I'm really impressed how it looks and finished. I expected worse. Long lever with two lugs as a nice bonus.

I have the Crimaz cover and it didn't require a spacer.

It's definitely one of the most underrated upgrades you can put on a bike.

chandlerman I have Crimaz on my Special, without spacer too. Yes it is absolutely another level. And price too.

Maybe this one needs a spacer due to xmas tree shimmed to 0.75(not 0.5 as recommended in most cases). There also was no case and cover gaskets and clutch basket was not torqued properly. With 1 mm spacer there is noticeable free play on the lever, I'd say maybe 1mm is too much but still acceptable.

So time will tell.

The problem not gone.

All repeats agin. Despite engine is freshly rebuilt and have no air leaks.
I tried before:
- Fuel flow test
- Different fuel taps
- Tank cap breather
- Another fuel tank
- Another carburetor
- Different lengths of fuel pipe
- Changed stator plate
- Changed CDI

Nothing helps.

The last thing that I can assume is the piston. Pity but I forget to take photo again when it was disassembled.

I will try to explain: The piston have two pockets(green) - one is blind, but other have hole(blue) which protrudes to the "inside" of the piston, to the gudgeon pin bearing area. It was so from new. Can it causing my problem?
The less fuel in tank the earlier problem appears. For example: while on "reserve" I can't even hold 70 km/h for, lets say, 300-500 m. When tank is full - it rides really nice.

Seems pretty unlikely that the holes would have an effect that only appeared on a low tank.

I had an issue for ages where I twisted the fuel line as I put the tank in so it would only run right when it was full.
Assuming the carb is really ok, is there some way you can rig up a bottle or small container instead of the tank so you can see the effect of a short straight fuel line (with absolutely no chance of kinks?

No issue on that side of the piston.

Post a picture of the float top/float/needle. As you have tried fuel flow it's possible there is something wrong here.

Thanks Ginch and Jack221. Will do when I have time.

But same problem with float/needle on two different carbs?
One is almost new SHBC 20L, and other is absolutely new SHB 19.19

Both could have the same type of float top. Post a picture and it can be ruled out.

Finally I had time. Jack221 here is pictures of new SHBC 19.19:





Float marked as 6122.2 and have "A" on one side and "C" on the other:





I also have pair of SHB 16.10 F and SHB 16.15 F:

6122.2 AB float and 4 float bowl






6122.2 DC and 2





6122.1 EA and metal 6 (8361) bowl





And the last one is SHB 16.10:
6122.1 and metal 2 (6200)bowl





This float also has no notch as others

If there is an issue it will be the float seat. And in the picture of the new 19, there isn't any open hole(s) across the seat. This can be an issue with jetting richer than stock. I'm guessing the other carb is the| same.

Here is SHBC 20 L float seat. Same as 19?

The extra holes allow the flow to be smoother, which maintains a higher float level. Any way to add some? Looks hard to get into. But might go at an angle.

Here is what I think I be able to do. Red dots is holes that can be added easily. Blue dots is questionable holes. Any of this holes will be angled in different angles.
What drill bit I must use? I have on hands 1 mm, 1.5 mm, 2 mm, 2.5 mm(I think it is too much).

1 mm drill bit on the pictures:










Maybe it is also worth to drill bigger this fuel passage from fuel hose connector to needle seat? Now it is bigger than 1.5 mm but smaller than 2 mm.

I would go for 3 blue holes at 2mm. Angle doesn't matter. They let air in more than fuel out. Sure this is going to help.
Drill out that fuel inlet 5mm (if you can) and chamfer the edge off. This might be a worse issue than the needle seat.

Jack221 this is what I'd done.

2 mm holes




At first added 3.8 mm hole(5 mm is impossible IMHO) but then decide to grind off all ribs.

Looks great. Has to make a difference.