Modern Vespa

I replaced the Walbro and I have just a few questions about the new KEIHIN CVEK-2600A that I installed.

1. It fired up almost immediately after giving it fuel. That was a relief.

2. The idle speed sounds healthy. I don't have a tachometer, but it chugs along nicely.

3. On the side of the carburetor, there's a little L shaped hose. My initial "guess" is that this is where I need to connect the evap system which runs into a "T" connector below the charcoal container up under the side of the bike.

4. When I open up the throttle, it struggles, and never seems to get to speed, but doesn't sound like it's skipping strokes.

5. The hose coming out of the bottom is a waste hose, yes? I believe it just points down to the ground.


The service manual I have doesn't seem to explicitly address the number of turns on the carburetor screw near the float bowl. I would presume this is the adjustment I need to focus on.

Which direction is lean, and which direction is rich, and is this probably the problem?

L shaped tube is the vent for the float bowl. The one at the bottom is the drain tube for the same float bowl. The mixture screw affects the idle to maybe 1/8 of throttle. And you looking at about 2 1/4 to 2 1/2 turns out from bottoming out after turning the screw in clockwise. Don't go gorilla on it, easy does it, just turn in until you feel it stop. It requires a special "D" shaped socket to do this. Turning in (CW) leans it, turning out (CCW) richens the mix. If the idle is ok, maybe you should not mess with it and concentrate on the higher throttle response you are having trouble with. Was the carb attached to the airbox when you were trying to rev it and it was faltering? If so, Have you checked the air filter?

Hmm...I expected there to be a need for that special D shaped driver but it's actually a slot heat brass screw, so ... no need for it.

Only the carbs for the USA production had the Federal mandated D screw. The rest of the world is quite happy respecting the owners to be able to adjust the idle properly so provided a conventional slotted screw, and dealers would always adjust it for minimum CO2 at service time anyway.

don't attach the evap to the float bowl, just leave the little elbow on there and zip tie the line up under the frame strut.

new doesn't mean everything is perfect. I may have picked up some trash along the way. ensure that the jets are clean and that the slide operates properly.

you'll want to be about 2.5~3 turns out on the idle-- hot.

if you haven't upgrade the idle jet to #38

I haven't been following along; is everything else in good nick? intake manifold, intake, air filter, box is sealed, no leaky vacuum lines.