Re: 1972 johnson 125 outboard help!
If the engine backfires, it is possible one of the spark plug coils leads is switch onto another plug, causing 2 cyls to fire at the wrong time. If you double check and find the correct color power pack wires are driving the correct plugs, then you could have a fuel issue. If the carbs have any dried fuel restricting the carb passages, it can cause the engine to "sneeze" or miss occasionally. (This may appear to be a "backfire). Actually, it is a lean condition at idle due to an internal fuel restriction of dried fuel gel. This is a carb issue and would require them to be torn down and cleaned internally. (a common problem on engines that have not been run much or were improperly stored over the winter.) When first started, that engine will not have any water coming out of the exhaust relief holes at the top of the midsection. After you run it for a minute or more, the single thermostat (vernatherm) will open, and then a fine water/mist will come out of those holes. (that's good-indicates the pump and thermostat are working normally.) The fuel pump bolts to the starboard side of the engine. Remove the cowling and follow the fuel hose from the inside of the lower cowl-it is connnected to the fuel pump. Fuel hoses that go flat are definitely a problem. Could be a bad hose bulb (one or both of the ball valves are sticking), or a restriction at the tank. Are you using a built-in tank or remote 6 gallon tank? Check the anti-siphon valve on a built-in.
