‘W’ needle kit for Dellorto PHBG Carburetors. Needles are tapered differently, a less tapered needle will deliver less fuel through the throttle range, where a more tapered needle will allow more fuel through the throttle range. The W7, W8 or W9 needles are good places to start with most 50cc scooter with a 70cc kit and performance exhaust installed.
When tuning the needle, the needle is adjusted from 1/4 to 3/4 throttle. Typically the W16 needle that comes standard in the PHBG carb is orientated for race use, and is very rich in the mid throttle range. A rich needle often gives a bike the ‘full throttle or nothing’ feeling – where the engine splutters and does not make power at any throttle point but full throttle. As the needle is leaned off by either replacing it or dropping the clip (moving the locator clip on the end of the needle closer to the flat end of the needle, dropping the needle further into the atomizer) it will start the lean out the middle throttle ranges. As an example, moving from a W16 needle to a W7 or W9 needle will often ‘clean up’ the mid throttle range, which makes a tuned scooter alot more ridable on the street. This is a very basic explanation, but like all carburetor tuning – its best to start somewhere safe, and slowly make adjustments between test rides to see what affect it has on the way the scooter makes power.