d. Excessive Smoke Issues from Exhaust and Oil Spray Issues from Gear Case Breather Outlet. This is an indication that the scavenger pump is not draining engine crankcase and returning oil to tank. With engine running at idle speed, examine oil return in tank. Remove tank oil cap, and with a small flashlight (tactical situation permitting), observe whether or not oil is dripping from 1⁄8–inch hole in oil return tube. Hole is on under side of tube and is located just back of oil gage rod tube. If observation is poor, place finger over hole and feel for pulsation of oil pressure. If oil does not return to tank, scavenger pump is faulty. Should the crankcase breather valve be incorrectly timed, smoke will issue from the exhaust, but not as noticeably as when scavenger pump is not working. Refer to step e below for this condition.
e. Smoke Issues from Exhaust and Excessive Oil Condition Exists Around Cylinder Exhaust Ports (where exhaust pipes enter cylinders). Engine scavenger pump and crankcase breather valve are one unit, operated by worm gear located behind engine shaft pinion gear. Although scavenger pump is not “timed,” the breather valve sleeve which drives it must be timed to balance the engine lubricating system. If for any reason the scavenger pump unit is removed from engine base, the breather valve must be retimed (within the gear case) when pump assembly is replaced. Incorrectly timed breather valve will force oil past piston rings, causing some smoke, besides forcing oil out through exhaust ports, causing excessive oily condition around exhaust pipes where they enter cylinder ports.
31. FUEL SYSTEM.
a. Many symptoms which might be attributed to the air‐fuel system are, in reality, due to faulty ignition. Before attempting any but the obviously required adjustments, check the ignition system thoroughly. Gasoline tank supply valve is a dual purpose valve, and its operation is explained in paragraph [5 b].
b. Shut off gasoline supply valve. Disconnect fuel line at strainer, open valve, and observe free flow of fuel from pipe. If line is plugged, remove, clean out, and replace.
c. Remove, disassemble, clean, and install fuel strainer (par. [72]).
d. Hard Starting, Spitting, and Misfiring Caused by Water in Fuel. Remove drain screw from carburetor bowl, drain bowl, and replace screw. Take care not to cross drain screw threads when replacing. If there is still evidence of water, dirt, or other foreign matter after bowl is drained, replace carburetor (pars. [70] and [71]). Remove air cleaner oil cup and inspect for evidence of water in oil. Drain, clean, refill to correct level mark, and replace cup. Should above procedure fail to eliminate trouble, drain fuel tank by removing drain plug located under tank in forward position. Replace drain plug and refill tank with fuel.
e. Hard Starting, or Missing at Idling and Low Speeds. Carburetor low speed circuit in need of adjustment (par. [68]). Carburetor high speed circuit is controlled by a fixed jet.
f. Impossible to Obtain Satisfactory Carburetor Adjustment: Lean Spot Between Idling and Up to 30 Miles per Hour Speeds. Carburetors in service for some time become dirty and crust forms in the throttle barrel, making satisfactory low speed adjustment difficult, if not impossible. Replace carburetor (pars. [70] and [71]).
g. Fuel Leaking from Carburetor. Evidence of dirt in float valve, incorrect float level, or faulty float. Replace carburetor (pars. [70] and [71]).