Piaggio zip carb

The slide controls how much air can be drawn through the carb. The slide is controlled by the throttle cable. When the throttle is twisted, it opens up the slide, allowing more air and fuel to be drawn into the engine, producing power and increased revs.

Attached to the base of the slide is the needle. The needle moves in and out of the fuel feed tube which is where the fuel is fed up from the bowl into the carburetor. At the bottom of the fuel feed tube is the main jet.

This is a top to bottom explanation, slide, needle, fuel feed tube, main jet, bowl. Needles are tapered, like a spike. At the throttle fully closed position the needle is sheathed all the way into the fuel feed tube, effectively closing it off. As throttle is applied and the slide opens, this lifts the needle with the slide, allowing fuel to be drawn up through the main jet and the fuel feed tube. The taper of the needle effects the amount of fuel that can be drawn at once through the fuel feed.

This needle has a heavy taper, meaning its thin and pointy to put it simply. The heavy taper means that at low to middle throttle, the thinner needle allows more fuel to flow through the fuel feed tube, causing the engine to run richer. These needles are less tapered, and thicker. This has the effect of leaning the low to middle throttle range out, and giving the bike a more consistent power delivery through the rev range — where the W16 is far too rich in these areas.

The main jet is the main method of controlling rate of fuel flow to the engine. The needle controls how much of that fuel the engine gets between idle and full throttle. At idle and full throttle, the needle has no effect. At full throttle the needle is all the way out, its done its job. For this reason, its important to always centre tuning around the main jet. Get the main jet right, then knit pick the rest of the fuel delivery. The other major part of carb tuning is the pilot jet.

In basic terms the pilot jet is responsible for maintaining a constant level of fuel to the engine while its running. At idle for instance when the needle is either all or almost all the way in, and not allowing the main jet to supply fuel to the engine — it still needs fuel. This is where the pilot jet kicks in. In most cases, the factory pilot jet can be left alone. The pilot jet also acts as a sort of reserve of fuel for the engine to have ready for when throttle is rapidly opened.

This is because there is a short delay in supply when lots of fuel is suddenly required from the main jet, as it needs to travel up the fuel feed, past the needle, ect.. Panicking and changing 5 things to try to fix a tuning issue often leaves you worse off than you were originally, and you have no idea what change did what. Maybe one of the changes was right, but the other four changes were wrong and hid the benefit made by the right one?

Tuning is alot of trial and error. Changing one part at a time is the only way to distinguish error from correction.

As stated above, the main jet is the most important tuning aspect to get correct. If the main is too lean, you run the risk of seizing the piston. If its too rich, the plug will foul and the bike will make alot of smoke and not go far. Theres a reason for this huge difference in jet, you guessed it too — its carb size. Bigger carbs require a smaller jet, as a general rule. This is normal. For this reason, the best port of call generally is to start with the standard jet included in the Malossi Carb kit.

Its often pretty close. That does NOT mean you can bolt the carb in and expect it to ride well without further tuning, but as a starting point its a solid start. The other big sign is the burn colour on the spark plug. Start the bike up, rev it on the stand to see how it sounds. Make sure its revving keeping in mind the choke will effect things in the first couple minutes of running. If its spluttering and not going anywhere fast, trying going down in the main jet. When you get back, check the plug against the above chart.

The plug check is only really to confirm what you already feel, the way the bike feels under acceleration is your main guide. The correct way to go about changes in jets and needle is ONE setting at time — by this I mean if you ride the bike with a 70 jet and it feels a little lean, go up to a 72 or a Even better, this kit gives you the option of Auto-choke, manual flip choke. The manual cable choke option includes the choke mechanism, cable and the lever unit for a full fitment kit ready to bolt on.

Depending on your airbox, some modofication may be required to get the carb inlet to fit inside the airbox outlet as the PHVB inlet is larger than the stock carb. Our PHVB carb kits are available in 2 different sizes, This Generally, a performance carburetor is bigger than a standard factory carb, which allows the engine to suck more fuel and air — which in turn gives you more power.

Malossi have put years of research and development into these carbs, and have chosen the exact specifications of the Dellorto PHVB because of its high quality, performance value and ability to be precision tuned. It uses the standard auto-choke from the standard PHVA This particular carb comes in 3 different kit versions. The only difference between the 3 kits is the choke mechanism. The Auto-Choke kit comes with a dellorto style choke, to suit the factory Piaggio plug connection.

The Manual Choke kit comes with a manual flip choke, which is a great compact little unit which is completely built into a simple lever attached directly to the carb.