Chainsaw Repair

Hi Joe,
Be careful with the B12.  That stuff is known to melt the check valves inside the high speed nozzle. Walbro HDA-268 doesnt have a replaceable nozzle fwiw so if you melt it you will need to make some other arrangements.  I may be telling you something you already know?  There are two kinds of check valves in the H side of the walbro carbs.  i. is a capillary seal type and ii. is a mechanical seal.  The reason that the check valve is needed is to keep the baro pressure from getting down inside the metering chamber of the carb.  Symptoms of a leaker is an idle mixture that wont tune.  One moment lean the next rich and so on.  Wont accelerate from an idle (bog).

The black plastic 'scoop' that is in the air filter is a spit back plate.  In a piston ported engine, the piston skirt closes off the intake.  When this happens any speed that has accumulated in the intake track slams into the skirt.  Air itself doesnt really have a whole lot of impact, but once mixed with fuel is heavy and thick.  The inertia of the fuel bounces off the skirt and splashes out into the air filter.  The spit back plate is there to catch this and keep it out of the atmosphere. 

Thanks for the pics on the throttle plate adjustment.  I could see where this would make a big difference on the high speed hit.