I have observed that 8F models with 4Y engine develop a "long crank time" issue as the LP regulator ages. We have determined this to be caused by the secondary valve becoming leaky which will permit the primary fuel chamber to empty through the secondary valve while the engine is shut off. This effectively "floods" the engine and makes it necessary to crank the engine for a long time while holding the accelerator to the floor, or wait long enough for the engine to just clear itself (could be hours) after the primary chamber is fully depleted and the engine has vented the excessively rich mixture.
Sometimes you will be able to detect the smell of LP odorant at the intake air grille on the right side rear overhead guard pillar when the secondary valve is not seating.