Dasboatman
Well-Known Member
- Joined
- Jun 12, 2005
- Messages
- 1,103
Hey Neil,
Where are the tank pick ups and vents located. Pickup in Port lower corner, vemt in Starboard upper corner for all tanks will cure a lot of problems. Sounds like the plumbing lines are the correct size. What are the sizes of the tanks. The second tank feeding the hopper tank being 1/2 full after only 3 to 4 laps sound like a high fuel consumption.
Have you made sure the tanks, hard and flex tubings are not leaking when assembled as a unit?? I agree with Phil - an 18# Scale boat is getting up there for a MAC. They are notorious for no bottom end power - High RPM top end is their strong point. I'm still amazed Joe Ingrao's Red Man ran as well as it did being very heavy and running a MAC.
Some pics of your installation would be of benefit also for those of us that like show and tell to attempt to troubleshoot. Here's and oldie but Goodie FYI: CHEERS !!! Bob
Troubleshoot your fuel system
Radio Control Boat Modeler, Feb 2004 by Finch, John
Fuel-draw fixes
In my article "How to power-tune your carb" in the December 2003 issue, I said that I would cover the real-life problems that occur at the pond, rather than what should happen there. Many years ago, my friend Don Pinckert told me that when he worked in a hobby shop, most of the problems that his customers encountered with engine performance were related to fuel systems. Over the years, I have seen exactly what he was talking about. I believe that about 80 percent of all engine problems are related to fuel-or the lack of it. All too often, boat modelers change setups, props and pipes-or replace engines-when their difficulties are due simply to fuel-draw problems.
FUEL-DRAW SYMPTOMS
Symptoms that are indicative of fuel-draw problems include (but are not limited to): the engine runs rich one minute and lean the next; the engine runs cool and then, minutes later, it overheats; or the engine performs well on the first lap but then switches to a lean setting a few laps later. The biggest clue to a fuel-draw problem is the inability to get a good needle setting on the starting table.
CAUSES OF FUEL-DRAW PROBLEMS
For an engine to run consistently, its carburetor must be getting a continuous flow of fuel. The fuel system should deliver fuel only to the carburetor; the air intake to the carburetor should deliver only air. Air and fuel are mixed in the carburetor, and the ratio of air to fuel is the key to optimum performance. The needle valve is the tool that we use to adjust how much fuel enters the carburetor to get the proper air/fuel mixture for top performance.
Anything that adds air to the fuel line or changes the pressure of the fuel in that line will cause mixture problems in the carburetor. A pinhole leak in the fuel line causes air to be sucked into the fuel, thus making the air/fuel mixture go lean in the carb. Air bubbles from the fuel tank that are sucked into the fuel line may also cause the engine to go lean. Pinholes or small tears in the fuel line are usually difficult to see. They are most commonly found on the fuel line where it's attached to the metal fuel-tank tube. An inadvertent push on the fuel line can cause a tear, as the brass fuel tube can be sharp. More often than not, you must bend the fuel tubing to expose the tear. It isn't something that jumps right out at you; you have to actively search for it.
Garbage in the fuel also causes fuel-draw problems. If you don't use a fuel filter, debris will enter the fuel system, and it will block the flow of fuel to the carb. The blockage will reduce fuel flow to the engine, and again, the engine will go lean. When you fill the fuel tank, use a fuel filter between it and the fuel jug, and use a filter between the tank and the engine to prevent debris from entering the needle valve.
If you have an engine that operates well for a few laps and then quits, look for "trash" inside the tank or a crack halfway up the pick-up tube on the inside of the tank. When the tank is full, the engine operates well because fuel is drawn into the crack as well as into the tube opening. The problems start when the fuel level drops below the crack in the tubing because at that point, air is introduced into the tube and then drawn into the engine.
I once had an engine that ran rich and then lean and then sputtered on the start stand. I changed the fuel tank, and the problem went away. I flushed the troublesome tank several times, but it still caused problems when I reinstalled it on the model. Frustrated, I cut it open and found a piece of paper towel that was obviously getting sucked up as far as the opening of the pick-up tube, but it was too large to be sucked into it.
Bits of red rubber that I found inside the tank caused a similar problem. Further investigation revealed that my red fuel bulb was deteriorating. I had used the bulb to flush the tank after a day at the pond, but instead of cleaning and flushing the tank, I was inadvertently adding red fuel-bulb debris to it. The lesson: use a fuel filter even when you flush your tank.
Changes in fuel pressure will change the amount of fuel that gets to the carburetor as well. Most high-performance engines use pipe pressure to help deliver ample fuel to the carb. This is accomplished by running a line between the tuned pipe and the tank's vent line. The pressure in the tuned pipe is diverted to the tank to help push fuel toward the engine. A leak or blockage in the pressure line will change the amount of fuel delivered to the carburetor, so pay as much attention to the pressure line as you would to the fuel-delivery line. If the pressure line pops off while the boat is running, the engine will most likely lean out from lack of fuel, and then it will quit.
FUEL-TANK SETUP
If you don't know the proper setup techniques, you could create your own fuel-draw problems when you design your fuel system. If you use two or more tanks without understanding how pressure changes between tanks affect the engine, it may run rich after the first tank has emptied because the fuel is drawn more easily then. This will be evident if your boat runs great halfway through the race but then goes rich on the last few laps. You could set up the tanks with two super-large fuel lines running from one tank to the other, but a better solution would be to run tanks of different sizes with a small sump tank that never completely empties closest to the engine. The pressure will remain the same because only the main tank will lose fuel.
It's a very good idea to use a sump tank with all fuel systems. Large tanks can lose fuel draw when they're low on fuel because the fuel sloshes away from the pick-up. A small tank between the main tank and the engine will always stay full. The small tank's fuel level may change when the main tank that feeds it loses draw, but the small sump tank loses only a little fuel off the top. For this reason, metal fuel tanks are usually built with small tanks inside them. The sump is usually built to hold about 1 ounce or less of fuel right around the pick-up tube. When it sloshes forward, the fuel is trapped right at the pick-up; when the fuel sloshes back to the sump, the sump then fills completely again. The fuel pick-up should be positioned at the tank's bottom-left rear so that when the model turns to the right on the race-course, the pick-up will be where the fuel sloshes during the turn. The vent line should be at the top forward area of the tank.
I like to use a fuel bulb to pressurize my fuel lines; I force fuel into the line, and if there is a tear, fuel leaks out right there. I use the bulb for finding waterline leaks, too.
The best advice I can offer is to always use a fuel filter.
So the next time your engine acts up, check out the fuel system before you start fussing with the engine. Happy boating!
Copyright Air Age Publishing Feb 2004
Where are the tank pick ups and vents located. Pickup in Port lower corner, vemt in Starboard upper corner for all tanks will cure a lot of problems. Sounds like the plumbing lines are the correct size. What are the sizes of the tanks. The second tank feeding the hopper tank being 1/2 full after only 3 to 4 laps sound like a high fuel consumption.
Have you made sure the tanks, hard and flex tubings are not leaking when assembled as a unit?? I agree with Phil - an 18# Scale boat is getting up there for a MAC. They are notorious for no bottom end power - High RPM top end is their strong point. I'm still amazed Joe Ingrao's Red Man ran as well as it did being very heavy and running a MAC.
Some pics of your installation would be of benefit also for those of us that like show and tell to attempt to troubleshoot. Here's and oldie but Goodie FYI: CHEERS !!! Bob
Troubleshoot your fuel system
Radio Control Boat Modeler, Feb 2004 by Finch, John
Fuel-draw fixes
In my article "How to power-tune your carb" in the December 2003 issue, I said that I would cover the real-life problems that occur at the pond, rather than what should happen there. Many years ago, my friend Don Pinckert told me that when he worked in a hobby shop, most of the problems that his customers encountered with engine performance were related to fuel systems. Over the years, I have seen exactly what he was talking about. I believe that about 80 percent of all engine problems are related to fuel-or the lack of it. All too often, boat modelers change setups, props and pipes-or replace engines-when their difficulties are due simply to fuel-draw problems.
FUEL-DRAW SYMPTOMS
Symptoms that are indicative of fuel-draw problems include (but are not limited to): the engine runs rich one minute and lean the next; the engine runs cool and then, minutes later, it overheats; or the engine performs well on the first lap but then switches to a lean setting a few laps later. The biggest clue to a fuel-draw problem is the inability to get a good needle setting on the starting table.
CAUSES OF FUEL-DRAW PROBLEMS
For an engine to run consistently, its carburetor must be getting a continuous flow of fuel. The fuel system should deliver fuel only to the carburetor; the air intake to the carburetor should deliver only air. Air and fuel are mixed in the carburetor, and the ratio of air to fuel is the key to optimum performance. The needle valve is the tool that we use to adjust how much fuel enters the carburetor to get the proper air/fuel mixture for top performance.
Anything that adds air to the fuel line or changes the pressure of the fuel in that line will cause mixture problems in the carburetor. A pinhole leak in the fuel line causes air to be sucked into the fuel, thus making the air/fuel mixture go lean in the carb. Air bubbles from the fuel tank that are sucked into the fuel line may also cause the engine to go lean. Pinholes or small tears in the fuel line are usually difficult to see. They are most commonly found on the fuel line where it's attached to the metal fuel-tank tube. An inadvertent push on the fuel line can cause a tear, as the brass fuel tube can be sharp. More often than not, you must bend the fuel tubing to expose the tear. It isn't something that jumps right out at you; you have to actively search for it.
Garbage in the fuel also causes fuel-draw problems. If you don't use a fuel filter, debris will enter the fuel system, and it will block the flow of fuel to the carb. The blockage will reduce fuel flow to the engine, and again, the engine will go lean. When you fill the fuel tank, use a fuel filter between it and the fuel jug, and use a filter between the tank and the engine to prevent debris from entering the needle valve.
If you have an engine that operates well for a few laps and then quits, look for "trash" inside the tank or a crack halfway up the pick-up tube on the inside of the tank. When the tank is full, the engine operates well because fuel is drawn into the crack as well as into the tube opening. The problems start when the fuel level drops below the crack in the tubing because at that point, air is introduced into the tube and then drawn into the engine.
I once had an engine that ran rich and then lean and then sputtered on the start stand. I changed the fuel tank, and the problem went away. I flushed the troublesome tank several times, but it still caused problems when I reinstalled it on the model. Frustrated, I cut it open and found a piece of paper towel that was obviously getting sucked up as far as the opening of the pick-up tube, but it was too large to be sucked into it.
Bits of red rubber that I found inside the tank caused a similar problem. Further investigation revealed that my red fuel bulb was deteriorating. I had used the bulb to flush the tank after a day at the pond, but instead of cleaning and flushing the tank, I was inadvertently adding red fuel-bulb debris to it. The lesson: use a fuel filter even when you flush your tank.
Changes in fuel pressure will change the amount of fuel that gets to the carburetor as well. Most high-performance engines use pipe pressure to help deliver ample fuel to the carb. This is accomplished by running a line between the tuned pipe and the tank's vent line. The pressure in the tuned pipe is diverted to the tank to help push fuel toward the engine. A leak or blockage in the pressure line will change the amount of fuel delivered to the carburetor, so pay as much attention to the pressure line as you would to the fuel-delivery line. If the pressure line pops off while the boat is running, the engine will most likely lean out from lack of fuel, and then it will quit.
FUEL-TANK SETUP
If you don't know the proper setup techniques, you could create your own fuel-draw problems when you design your fuel system. If you use two or more tanks without understanding how pressure changes between tanks affect the engine, it may run rich after the first tank has emptied because the fuel is drawn more easily then. This will be evident if your boat runs great halfway through the race but then goes rich on the last few laps. You could set up the tanks with two super-large fuel lines running from one tank to the other, but a better solution would be to run tanks of different sizes with a small sump tank that never completely empties closest to the engine. The pressure will remain the same because only the main tank will lose fuel.
It's a very good idea to use a sump tank with all fuel systems. Large tanks can lose fuel draw when they're low on fuel because the fuel sloshes away from the pick-up. A small tank between the main tank and the engine will always stay full. The small tank's fuel level may change when the main tank that feeds it loses draw, but the small sump tank loses only a little fuel off the top. For this reason, metal fuel tanks are usually built with small tanks inside them. The sump is usually built to hold about 1 ounce or less of fuel right around the pick-up tube. When it sloshes forward, the fuel is trapped right at the pick-up; when the fuel sloshes back to the sump, the sump then fills completely again. The fuel pick-up should be positioned at the tank's bottom-left rear so that when the model turns to the right on the race-course, the pick-up will be where the fuel sloshes during the turn. The vent line should be at the top forward area of the tank.
I like to use a fuel bulb to pressurize my fuel lines; I force fuel into the line, and if there is a tear, fuel leaks out right there. I use the bulb for finding waterline leaks, too.
The best advice I can offer is to always use a fuel filter.
So the next time your engine acts up, check out the fuel system before you start fussing with the engine. Happy boating!
Copyright Air Age Publishing Feb 2004
