Tell Tale Signs of a Walbro Carb needing Attention
Walbro carbs are (by nature) very stable and dependable. Once your engine broken-in, you shouldn't need to mess with the carb. If you find yourself having to re-tune or you use the choke more often than usual, there's a problem. 75% of the time, the problem can be traced to the internal filter screen. These screens are super-fine mesh and easily clog.
The first and most obvious sign of a clogged screen is, your engine is running lean on the topend, and requires re-tuning. As the clog gets worse, both the topend and the lowend needles will require re-tuning. Eventually, you will have to choke your engine more often to get it to fire up. This is the worst-case scenario.
All Walbro's have a filter screen, however some have TWO screens! If your carb has two screens, both will require cleaning and/or replacement.
The primary screen is located on the PUMP SIDE of the carb. Remove the single screw in the middle pump cover and lift it off. When you re-assemble the carb make sure the pump diaphragm goes on the carb first followed by the gasket.
The fine mesh screen can be removed using an Exacto Knife or other sharp tool. Catch the screen on the edge and lift up. I'd like to NOTE here, that the visible side (cup side) is the debris trap. So most of the crap will be visible before you remove the screen. You can't properly clean the screen without removing it! The "real" crap is wedged into the mesh and has to be blown out from the back side. I would HIGHLY RECOMMEND you thoroughly clean the carb before you re-assemble it. Once you've back-flushed the screen and it shows to be clean, re-install the screen making sure it is completely seated as it was originally. The back-side of an Exacto Knife makes a great installation tool for the screen! While you have the carb dis-assembled inspect your diaphragms. These do get old and wear out. Carb overhaul kits are cheap and very much worthy of installing since you're working on the carb anyway.
IF your Walbro has a Secondary Screen, it will be located on the "float" side of the carb. You will have to remove the 4 screws holding the float diaphragm cover, and remove the float diaphragm. If you see a brass insert as shown in the photo, there's a screen below that insert. DO NOT attempt to remove the insert & screen! You will damage both. All you need to do is BACK-FLUSH the screen through ONE of the tuning needles. The way to do this is, close off ONE of the needles, and remove the other. Using an aerosol carb cleaner pressurize the carb through the removed needle hole. CAUTION!!! Do not get carb cleaner in your eyes!!! I can't even begin to tell you how painful and damaging this is to your eyes! So please use a face shield! When the secondary screen is completely back-flushed, the carb cleaner will flow readily through the insert. When you're done, re-assemble the carb and adjust BOTH needles to the factory settings. This is typically 1.75 turns on each.
Some kits include filter screens and some don't. If your kit has the screen use it.
The Walbro Kit Number for all WT carbs is: K20-WAT