Modern Vespa

I'm debugging a fuel delivery problem on my 2006 LX150 with a Keihin CVK KT. I'm struggling with it since neither my Haynes manual nor the Workshop manual describe this exact model. I'd hoped that a thorough cleaning would resolve it, but no luck, so now I need to understand it a bit more to further my debug:

1. Is there anything to adjust on it? Haynes and Workshop refer to the flow screw or pilot screw, that needs to be backed out by two turns. Mine doesn't have that. I have a screw that looks similar (1st picture), but its purpose is to drain the float bowl (2nd picture).
2. What causes the diaphragm (3rd picture) to move up against the spring (thus causing the needle to unblock a fuel passage (4th picture)? It doesn't seem there is any vacuum source behind the diaphragm that would pull it up.
3. What is the port for that has this hose sticking out of it (5th picture)? This hose is connected to some canisters. I suppose that this is sucking unburnt fuel vapor into the carb for emissions purposes, probably has nothing to do with the operation of the carb.

FWIW, my VIN is ZAPM448FX65004931, engine # is M443M5115

Thanks!
Toby

The pilot (aka air fuel mix screw) is located next to the carb heater (the thing with the black boot) and is brass with a D shaped head.

That screw in the picture is the float bowl drain.

The hose is an evap hose, disconnect it. It's unnecessary.

The vacuum for the slide is generated by the air flow through the Venturi of the carb. I'm over simplifying here, but basically that's the idea of it. It is also why a tuned intake tract is critical with CV carbs.

Anyway, if you didn't remove the air/fuel mix screw then the likelihood of the carb being clean isn't great. So I'd be giving that another go.

Sometimes older carbs just can't be made to work. I've had a few kiehn carbs over the years that I couldn't get to work no matter what I did. I think what happens is some of the interior fuel passages, slides, and other nonreplaceable parts get clogged or worn and they're just not possible to clean or to repair due to small size and inaccessibility. They are not that expensive and you might save yourself a whole lot of grief just by buying a new or replacement carb.

Yes, I saw that thing, but with it's tamper-proof head, I assumed it was something that was not intended to be serviced. I see carburetor adjustment sets on Amazon that have the right shape, hopefully it's a universal fit. I'll remove it and soak the carb in cleaner again. Thanks for the suggestion! Lars - probably sound advice, but I never replace anything if there is a chance of fixing it! It must be some manifestation of OCD in me, but I always feel why replace that whole thing when there is just some tiny part of it that is bad, if only I can figure out what it is...

Yep, that's the mix screw. Spraying carb cleaner thru all openings followed by high pressure air usually works. But if you have access to a sonic cleaner, that really the way to go. I used to use chemical carb cleaner (dunking the whole carb), but over time the stuff wears out, stinks up the place, must be used in fresh air environment (open garage doors) and the newer stuff on the market is on the tame side. 15 to 30 minutes in the hot sonic tank will do the trick almost every time.

Be careful when you remove the mix screw. There should be a spring, small washer and o-ring. The last two items may get stuck up in there and have to be removed with a small wire with a slight hook on the end. The o-ring will most likely be toast, so plan on replacing it.