Stromberg Emission Carbs
Prior to attempting any carb mixture or idle adjustment, it is important to maintain an “airtight” engine interior and vent hose system, (IE: crankcase and valve cover sealing), and vent hose system on Stromberg emission carbs where the crankcase fumes are vented into the low pressure area of the carb, via the valve cover. (this vent system can be identified by following the hose from the valve cover to the midpoint of the carb body). This system integrity can be partially tested by removing the oil filler cap and noting a significant change in engine idle speed. A more positive test is to apply 1 to 2 PSI pressure at the valve cover hose thus pressuring the engine crankcase and noting areas of air leaks. DO NOT EXCEED 2 PSI.
Common leak areas are the valve cover stud holes, valve cover gasket and vent hoses connections, The vent hose becomes hard and brittle with age and poor sealing results. Periodic replacement of the vent hoses to ensure a tight fit on ALL connections is recommended. The vent hose connection at the carb is particularly important and is often overlooked, or, the nylon hose adapter is missing/broken. Other areas that effect engine air-tightness are; engine front plate/pan gasket, timing cover gasket/seal, rear crankshaft seal, fuel pump mounting gasket/seal.
An area often overlooked with the vent system is the restrictor in the charcoal fuel vapour canister. When missing, and many are, the unrestricted air flow will cause mixture control problems. This restrictor can be identified as a nylon insert in the center tube on the top of the canister. Removal of the main canister vent hose, (the hose leading from the valve cover), can pull-out this restrictor resulting in loss of vacuum control in the engine vapour system.