I am servicing my MZ Skorpion which has a made by Yamaha 660 5 valve single. Like the raptor quad or Yamaha XTZ.
I'm going to clean the carb out...it is a dual unit, it has a primary carburetor and a secondary carb of sorts. The idea is that the secondary unit kicks in at some point in the RPMs...you can tell if you twist the throttle good, it gets a really throaty sound.
The secondary side has a butterfly that operates with the throttle cable/linkage and a throttle slide/needle that is operated by a diaphragm....it also has a return spring like any other throttle slide....the secondary slide is made out of a composite.
The diaphragm is in good shape. I cant for the life of me figure out how the secondary throttle slide manages to operate.
The diaphragm is made such that it would take vacuum on top of the diaphragm to open the slide. However, the only port on that side of the diaphragm leads to a right angle pipe. to which was attached a rubber hose with an inline mesh filter that was simply tucked back by the airbox....as in it is just a vent. And yet when i sucked in on it, the slide indeed opened.
So with only a vent on top of the diaphragm....and a normal slide spring keeping the secondary slide down...how does this work????
Again, the butterfly at the throat of the secondary does open mechanically....so some air is introduced that way.
Any ideas?
