Friday, May 1, 2009

FARMALL 560 CARB #3


This is the venturi. It controls/sets the vacuum level in carb. I think is 13 inches of vacuum that all carbs are supposed to operate at for the best efficiency. Don't hold me to the accuracy of 13 inches. I could be wrong on that number. However, there is a number that is right and all the numbers off from that could show boring and stroking the engine, stuck valves, bad rings, and even manifold leaks.
This is a stock venturi for a 560 Farmall. It is a #33 . I am putting a custom made venturi in to increase air flow and horsepower. As the engine is running it pulls air through the venturi, the smaller the hole the less air and higher vacuum. When you build the engine and port and polish the head or bore and stroke the engine you increase air flow which increases the vacuum. If you have too much vacuum the carb will not work properly. The carb has to be balanced so I put in a larger venturi to reduce the vacuum and feed more air through the carb to the engine. More air more fuel= more power.
The grooves on the outside of the venturi help balance the carb. The vacuum generated for the backside of the venturi helps to set the air/fuel ratio which controls how the engine runs and idles. It takes a combination of adjusting the air/fuel ratio screw and the main jet to get the fuel set properly.
I learned what I know by working on my carbs and my assumptions about how things work may be totally wrong. I had a man build the carb for my Super MTA pulling tractor. That was the best $350 I ever spent. I had worked on my carb for about 1-1/2 years and have about 15 different venturis here that I tried and I was tuning it in, but it probably would have taken me another1-1/2 years to get it right. I looked at the carb I had built and realized I was on the right path by just not far enough along the path. Sometimes it pays to buy the experience!
Eric Benton
Southeast Tractor Parts, Better parts because of the education!

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