TN-25
Chief Petty Officer
- Joined
- May 27, 2008
- Messages
- 623
Re: 1952 johnson 5hp no spark..
When Johnson referred to the 5 as having twin carburation, what they really meant was they used two different means of carburation. The carb actually doesn't even come into play until about half throttle. The old 5 is a not a reed valve 2-stroke, it is a rotary valve 2-stroke. At low speed the fuel is drawn in by gravity and vacuum to the crankcase, where it is pressurized through part of the cycle before a third port opens and the fuel charges into the combustion chamber. Have you noticed how the fuel line splits into an inverted Y at the front of the block? One goes to the crankcase, the other goes to the carb on the side. There is a little long lever on the front of the block that hangs down low and just juts out at an angle below the lower shroud. That long L-shaped lever meters fuel, and turns your low speed fuel flow to the crankcase on or off. IT NEEDS TO BE OPEN FOR STARTING. More correctly it will need to be opened and fine tuned for low speed running. Similarly it can actually be shut off when you are running high speed,(not that you would need to but it is possible).
When Johnson referred to the 5 as having twin carburation, what they really meant was they used two different means of carburation. The carb actually doesn't even come into play until about half throttle. The old 5 is a not a reed valve 2-stroke, it is a rotary valve 2-stroke. At low speed the fuel is drawn in by gravity and vacuum to the crankcase, where it is pressurized through part of the cycle before a third port opens and the fuel charges into the combustion chamber. Have you noticed how the fuel line splits into an inverted Y at the front of the block? One goes to the crankcase, the other goes to the carb on the side. There is a little long lever on the front of the block that hangs down low and just juts out at an angle below the lower shroud. That long L-shaped lever meters fuel, and turns your low speed fuel flow to the crankcase on or off. IT NEEDS TO BE OPEN FOR STARTING. More correctly it will need to be opened and fine tuned for low speed running. Similarly it can actually be shut off when you are running high speed,(not that you would need to but it is possible).