Post by Admin on Feb 25, 2012 9:38:30 GMT -5
How can something with only 2 moving parts be such a pain in the butt..... one word; methanol.
The problem is that methanol wants to absorb moisture. And when it does the resulting compound is jelly. And since the carb is loaded with lots of small orifices, things can get clogged up in a hurry.
Nine out of ten times, when the engine just won't run right; the carb is the problem. We've field stripped it more than once and it's a whole lot easier to do in the shop as opposed to in the dark with lots of dust.
Any problems we've had have been the result of not flushing the carb the day after a race. Our Slingshot has a purge system which is a 3 way valve mounted accessable to the driver. It has 3 positions: OFF, ON and PURGE. Aside from the benefit of my driver being able to shut off the fuel if he had to, the purge system has a hose that runs to the rear of the car. By switching the valve to purge, we are able to run the engine with that rear hose dipped into about a pint of gasoline. The gas is drawn through the fuel pump, fuel pressure regulator, into the carb, and any methanol is removed from the system. Gasoline will sit just fine in the carb without degrading from race to race like methanol will. When we're purging the system, we know it's complete since the engine will want to stall and you can smell the gasoline from the exhaust. We found it was not enough just to run the system empty since there was always enough methanol left in the carb to cause problems.... purging is the way to go but in order to do it safely and effectively, the purge accessory from Tobias is the only way to go.
We also disassemble the carb, usually on a monthly basis and clean everything out. This involves separating the core from the 2 elbows, removing the float compartment, and removing the jets. Both the 2 that are screwed into the float compartment that's removed as well as the jets behind the nuts below. I clean everything with Brake clean and blow all of the orifices out with air.
Remember to place the complex gasket between the core and the float compartment half on a piece of cardboard as soon as you remove it. Otherwise it will expand and be near impossible to get back into place.
We also remove the mixture screws and clean out those chambers. When you do, inspect the mixture needles to be sure they aren't bent or over compressed.
You will also notice a number a very tiny holes just into the barrels of the carb core... we spray them out. Any hole, any channel, the fuel stem, the overflow stem, etc,etc,etc get cleaned out. If you remove the float, take care since it is delicate. Make sure that the float needle is free and the float does not bind up in any way.
We've never had our carbs blueprinted but I'm told it makes a difference... snappier response. Tobias can blueprint them for you.
One other thing to watch for: The stop that prevents the carb from being over extended ( open ) is on the cable rod where the carb linkage is mounted to the engine. The stop that sets where the carb is closed is located on the rod at the accellerator pedal. Make sure that the stops are tightened in place so that the carb is fully closed with the pedal relaxed and the carb is fully open BUT NOT WITH ANY EXCESSIVE FORCE... however there should be a little bit of over travel each way.
Also, make sure anything you replace on the carb is from Tobias. The Briggs parts are not opened to the right diameters for methanol. The Tobias parts are opened to proper spec ( larger since it takes more methanol than gasoline to run the engine ).
We run the mixture screws around 3 to 3.5 turns CCW from closed. Rule of thumb is that if the weather is dry and crisp out, we run richer. If the weather is humid we run leaner since there is less oxegen in humid air than in dry air.
The problem is that methanol wants to absorb moisture. And when it does the resulting compound is jelly. And since the carb is loaded with lots of small orifices, things can get clogged up in a hurry.
Nine out of ten times, when the engine just won't run right; the carb is the problem. We've field stripped it more than once and it's a whole lot easier to do in the shop as opposed to in the dark with lots of dust.
Any problems we've had have been the result of not flushing the carb the day after a race. Our Slingshot has a purge system which is a 3 way valve mounted accessable to the driver. It has 3 positions: OFF, ON and PURGE. Aside from the benefit of my driver being able to shut off the fuel if he had to, the purge system has a hose that runs to the rear of the car. By switching the valve to purge, we are able to run the engine with that rear hose dipped into about a pint of gasoline. The gas is drawn through the fuel pump, fuel pressure regulator, into the carb, and any methanol is removed from the system. Gasoline will sit just fine in the carb without degrading from race to race like methanol will. When we're purging the system, we know it's complete since the engine will want to stall and you can smell the gasoline from the exhaust. We found it was not enough just to run the system empty since there was always enough methanol left in the carb to cause problems.... purging is the way to go but in order to do it safely and effectively, the purge accessory from Tobias is the only way to go.
We also disassemble the carb, usually on a monthly basis and clean everything out. This involves separating the core from the 2 elbows, removing the float compartment, and removing the jets. Both the 2 that are screwed into the float compartment that's removed as well as the jets behind the nuts below. I clean everything with Brake clean and blow all of the orifices out with air.
Remember to place the complex gasket between the core and the float compartment half on a piece of cardboard as soon as you remove it. Otherwise it will expand and be near impossible to get back into place.
We also remove the mixture screws and clean out those chambers. When you do, inspect the mixture needles to be sure they aren't bent or over compressed.
You will also notice a number a very tiny holes just into the barrels of the carb core... we spray them out. Any hole, any channel, the fuel stem, the overflow stem, etc,etc,etc get cleaned out. If you remove the float, take care since it is delicate. Make sure that the float needle is free and the float does not bind up in any way.
We've never had our carbs blueprinted but I'm told it makes a difference... snappier response. Tobias can blueprint them for you.
One other thing to watch for: The stop that prevents the carb from being over extended ( open ) is on the cable rod where the carb linkage is mounted to the engine. The stop that sets where the carb is closed is located on the rod at the accellerator pedal. Make sure that the stops are tightened in place so that the carb is fully closed with the pedal relaxed and the carb is fully open BUT NOT WITH ANY EXCESSIVE FORCE... however there should be a little bit of over travel each way.
Also, make sure anything you replace on the carb is from Tobias. The Briggs parts are not opened to the right diameters for methanol. The Tobias parts are opened to proper spec ( larger since it takes more methanol than gasoline to run the engine ).
We run the mixture screws around 3 to 3.5 turns CCW from closed. Rule of thumb is that if the weather is dry and crisp out, we run richer. If the weather is humid we run leaner since there is less oxegen in humid air than in dry air.