Frank Acampora
Supreme Mariner
- Joined
- Jan 19, 2007
- Messages
- 12,004
Re: 88 force 86hp. Say forever spent a fortune and no power under load
The fuel pump delivers in the range of 2-6 PSI fuel pressure. I do not know what values of vacuum and pressure are considered good for crankcase compression/vacuum. If you can get the engine to start at all, you can measure manifold vacuum which should be close to crankcase vacuum.
If you look closely at the pump. you will see that it is two stages. One stage is powered through a hole in the bypass cover. The secondary (smaller) stage is powered by a short hose from a fitting on the bottom (#3) cylinder crankcase. #2 crankcase vacuum pulls the large primary diaphragm in toward the block and pulls fuel through the screen and check valve. When the piston moves down, pressure forces the diaphragm outward. The check valve stops backflow and makes fuel flow through the middle check valve to the secondary stage. The two stages are 120 degrees apart because the crankpins are 120 degrees apart. The secondary stage pumps fuel to the carbs through the third check valve.
The fuel pump delivers in the range of 2-6 PSI fuel pressure. I do not know what values of vacuum and pressure are considered good for crankcase compression/vacuum. If you can get the engine to start at all, you can measure manifold vacuum which should be close to crankcase vacuum.
If you look closely at the pump. you will see that it is two stages. One stage is powered through a hole in the bypass cover. The secondary (smaller) stage is powered by a short hose from a fitting on the bottom (#3) cylinder crankcase. #2 crankcase vacuum pulls the large primary diaphragm in toward the block and pulls fuel through the screen and check valve. When the piston moves down, pressure forces the diaphragm outward. The check valve stops backflow and makes fuel flow through the middle check valve to the secondary stage. The two stages are 120 degrees apart because the crankpins are 120 degrees apart. The secondary stage pumps fuel to the carbs through the third check valve.