This primer bulb with a built-in plastic housing of rectangular (square) shape is intended for manual injection of fuel into the carburettor before starting a cold engine. By pressing the silicone cap, air is efficiently expelled from the system and the chamber is filled with fresh mixture, which drastically eases starting after the machine has stood for a long time. Fitting the new bulb completely solves the problem of false air being drawn in, which occurs when the old bulb hardens or cracks under the effect of petrol, directly preventing engine choking in operation and incorrect idle speed. When installing this model with two mounting holes and 28 mm spacing, it is extremely important to seat the rectangular housing flat on the base so that the sealing part is not left displaced. Before connecting the hoses to the connection nipples (outlets) of Ø4.4 mm and Ø3 mm diameter, check that the hose ends are elastic and seal well. Tighten the screws alternately and moderately so that the plastic housing does not crack under pressure, and before the first start press the bulb by hand a few times to check the tightness of the connections. Key characteristics Part type: Primer bulb with rectangular housing Manufacturer: high-compatibility aftermarket part Carburettor model: Walbro (series with square housing) Cap diameter (without housing): Ø15 mm Diameter with housing: Ø21 mm Mounting hole spacing: 28 mm Overall height: 23 mm Connection nipple (outlet) diameter: Ø4.4 mm / Ø3 mm Compatible models Machines with Walbro carburettors and a square mount: Trimmers, saws and blowers that use Walbro fuel systems with two mounting holes (Stihl, Husqvarna, Partner, Villager and other brands)