A lot of emphasis has been placed on carburetor pop-off pressures when in reality they are not an important issue to the service professional. In fact checking pop-off pressure can often damage the carburetor by stretching the fuel pump diaphragm and breaking the seal of the fuel pump gasket. Rather than pressurizing the carburetor to pop-off, Zama recommends that the carburetor should be pressurized at the fuel fitting to 10 p.s.i. It should hold this pressure for a minimum of 15 seconds.
Fuel Pump Diaphragms:
The tan Teflon coated pump diaphragm has been superseded by the clear mylar diaphragm. If your carburetor does not have a machined fuel pump surface you cannot use either the tan or the clear diaphragm. You must use the black buna diaphragm also found in the kits. All three diaphragms found in the Zama carburetor kits offer resistance to alcohol fuels.
Presetting the mixture screws:
Before carburetor L and H needles had limit caps the standard pre-set on the L and H needles was one turn open. When we had to begin using limiter caps we also decreased the needle sensitivity in many cases. So while we still try to have a preset of 1 turn, many needles fall between one and two turns open. Another thing we have tried to do is increase the clearance between the needle and the seat to make sure less debris collects there. This is because with the limit caps on it becomes much more difficult to remove the needles for cleaning. So while the limit caps have made it more difficult to preset the carburetor and to remove the needles, they have also made it less likely that the needles will get far out of adjustment, or that they will even need to be removed for cleaning.
L and H needles:
On many of the new emissions carburetors we reduced the sensitivity of the H needle to make it easier to precisely set the carburetor mixture. The H needle on some carburetors is now the same thread size as the L needle. This can lead to confusion if you take both needles out and do not identify them. Just remember that THE L NEEDLE IS ALWAYS LONGER!