Post by Scoutpilot on Jul 13, 2015 5:34:22 GMT -5
WARNING! When ever working around gasoline, always take the necessary precautions to contain any fuel spilled. Before removing the fuel pump make sure the engine is cool to the touch to avoid a fire. It would be a good idea to have a fire extinguisher handy in case something does go wrong.
TESTING THE FUEL PUMP
Unless you are completing a rebuild (more about that later), the fuel pump should always be tested on the motor. The line between the pump and tank is the suction side of the system and the line between the pump and carburetor is the pressure side. All connections should be mechanical. That is, threaded fittings. Alternatively, you can use barbed fittings for rubber tubing. But the use of rubber tubing as a permanent fuelline is discouraged because the rubber will swell and soften over time creating a restriction in the fuel line. Use of rubber tubing clamped to straight metal tubing is strongly discouraged due to the probability of the rubber becoming distorted or bunched up, creating a gap from which fuel can leak or air can be sucked in resulting in a loss of flow and pressure. A leak in the pressure side would be apparent because of dripping fuel. A leak in the suction side is usually only apparent because of a reduced volume of fuel delivered to the pressure side and sometimes bubbles visible in the glass bowl. If the threads in the pump ports and/or the carburetor fuel intake port are old and worn, then two (2) wraps of Teflon Tape or Plumbers Sealing Paste on the male fittings is recommended.
Tighten any loose line connections and look for any kinks or restrictions.
Disconnect the fuel line at the carburetor. Disconnect the distributor-to-coil primary wire. Place a quart container at the end of the fuel line and crank the engine a few revolutions.
If little or no fuel flows from the line, either the fuel pump is inoperative or the line is plugged. Blow through the lines with low pressure compressed air (remove or loosen the Fuel Tank Cap) and try the test again. Reconnect the line.
If fuel flows in good volume, check the fuel pump pressure to be sure.
Attach a pressure gauge to pressure side of the fuel line at the carburetor.
Run the engine at idle and note the reading on the gauge. It should be between 4 and 5 psi.
If the pump is operating properly, the pressure will be as specified and will be constant at idle speed. If pressure varies sporadically or is too high or low, the pump should be replaced or rebuilt.
Remove the pressure gauge. The following flow test can also be performed.
Disconnect fuel line from carburetor. Run fuel line into a suitable measuring container.
Run the engine at idle until there is one pint of fuel in the container. One pint should be pumped in 30 seconds or less.
If flow is below minimum, check for a restriction in the line.
The only way to check fuel pump pressure is by connecting an accurate pressure gauge to the fuel line at the carburetor level. Never replace a fuel pump without performing this simple test. If the engine seems to be starving out, check the ignition system first. Also check for a plugged fuel filter or a restricted fuel line or detritus in the tank. Be aware that some tank sealing systems will not withstand Ethanol and will deteriorate, break up and can clog the "J" tube in the tank.
OK. I promised to tell you about testing your pump after a rebuild. But first a little trick that will save you aggravation. You've gone through the pump, changed out the valves (hopefully you've placed them in their correct orientation) and the spring and the oil seal and the diaphragm. You struggled to line up the link, the pump arm, the diaphragm attachment slot and the pin. You've placed the top on the base, hopefully with the intake and outlet on the correct sides. Yes, it can be put together backwards. Now then, before you install the gasket, bowl and bail, tighten the screws to slightly less than snug setting. Then install the gasket, bowl and bail. Tighten the bail TIGHT. Place the pump arm in a vise and tighten it with the both arm rivets resting on top of the vise jaws. Screwdriver at the ready in one hand, pull the top all the way, full stroke, toward the vise and while holding it there, tighten the screws TIGHT. This procedure sets the diaphragm for the proper flex. The spring determines the pump pressure only when the diaphragm is set correctly. Failure to do this will result in poor performance from the pump.
TESTING THE FUEL PUMP
Unless you are completing a rebuild (more about that later), the fuel pump should always be tested on the motor. The line between the pump and tank is the suction side of the system and the line between the pump and carburetor is the pressure side. All connections should be mechanical. That is, threaded fittings. Alternatively, you can use barbed fittings for rubber tubing. But the use of rubber tubing as a permanent fuelline is discouraged because the rubber will swell and soften over time creating a restriction in the fuel line. Use of rubber tubing clamped to straight metal tubing is strongly discouraged due to the probability of the rubber becoming distorted or bunched up, creating a gap from which fuel can leak or air can be sucked in resulting in a loss of flow and pressure. A leak in the pressure side would be apparent because of dripping fuel. A leak in the suction side is usually only apparent because of a reduced volume of fuel delivered to the pressure side and sometimes bubbles visible in the glass bowl. If the threads in the pump ports and/or the carburetor fuel intake port are old and worn, then two (2) wraps of Teflon Tape or Plumbers Sealing Paste on the male fittings is recommended.
Tighten any loose line connections and look for any kinks or restrictions.
Disconnect the fuel line at the carburetor. Disconnect the distributor-to-coil primary wire. Place a quart container at the end of the fuel line and crank the engine a few revolutions.
If little or no fuel flows from the line, either the fuel pump is inoperative or the line is plugged. Blow through the lines with low pressure compressed air (remove or loosen the Fuel Tank Cap) and try the test again. Reconnect the line.
If fuel flows in good volume, check the fuel pump pressure to be sure.
Attach a pressure gauge to pressure side of the fuel line at the carburetor.
Run the engine at idle and note the reading on the gauge. It should be between 4 and 5 psi.
If the pump is operating properly, the pressure will be as specified and will be constant at idle speed. If pressure varies sporadically or is too high or low, the pump should be replaced or rebuilt.
Remove the pressure gauge. The following flow test can also be performed.
Disconnect fuel line from carburetor. Run fuel line into a suitable measuring container.
Run the engine at idle until there is one pint of fuel in the container. One pint should be pumped in 30 seconds or less.
If flow is below minimum, check for a restriction in the line.
The only way to check fuel pump pressure is by connecting an accurate pressure gauge to the fuel line at the carburetor level. Never replace a fuel pump without performing this simple test. If the engine seems to be starving out, check the ignition system first. Also check for a plugged fuel filter or a restricted fuel line or detritus in the tank. Be aware that some tank sealing systems will not withstand Ethanol and will deteriorate, break up and can clog the "J" tube in the tank.
OK. I promised to tell you about testing your pump after a rebuild. But first a little trick that will save you aggravation. You've gone through the pump, changed out the valves (hopefully you've placed them in their correct orientation) and the spring and the oil seal and the diaphragm. You struggled to line up the link, the pump arm, the diaphragm attachment slot and the pin. You've placed the top on the base, hopefully with the intake and outlet on the correct sides. Yes, it can be put together backwards. Now then, before you install the gasket, bowl and bail, tighten the screws to slightly less than snug setting. Then install the gasket, bowl and bail. Tighten the bail TIGHT. Place the pump arm in a vise and tighten it with the both arm rivets resting on top of the vise jaws. Screwdriver at the ready in one hand, pull the top all the way, full stroke, toward the vise and while holding it there, tighten the screws TIGHT. This procedure sets the diaphragm for the proper flex. The spring determines the pump pressure only when the diaphragm is set correctly. Failure to do this will result in poor performance from the pump.