Walter Atkinson
Well Known Member
Over the years, we have had difficulty operating carbed engines LOP for only one reason--they historically have poor F:A ratio balance. Even TCM and Lycoming have said that Cabred engines can't be run LOP. That is true if one assumes that you cannot balance the F:A ratios. However, as Conusious say, "Do not tell man something impossible when he already do it!"
I have personally run many carbed engines LOP with excellent success and repeatability. I know of several hundred others who are having the same success. Here is the issue.
A carburetor atomizes the fuel into small, medium, and large droplets. These droplets weight differing amounts and take different paths in the induction system. This results in varied F:A ratios among the cylinders. If one can get the fuel droplets VAPORIZED early in their progression, the F:A ratios will be quite even between the cylinders and the cylinders will have the same F:A ratio and therefore the same Hp output and will run smooth along the entire mixture spectrum.
One method to improve this vaporization has been to **** the throttle plate slightly to induce some turbulent airflow into the induction. This has been successful in some applications and not so successful in others. As it turns out, each engine and installation has an optimum carb temp which results in maximum vaporization and minimum heat required. Once that is discovered, simply setting that Carb Temp will result in maximum vaporization and optimum F:A ratios. As soon as that is accomplished the engine will run smoothly LOP.
How to find the optimum carb temp:
1) Set the engine monitor to the DIF function.
2) Add carb heat until the DIF is the lowest number you can get with the least amoutn of carb heat.
3) Note the Carb Temp. This same temp can now be set, winter, or summer, high or low to achieve the optimum fuel vaporization.
In a C-182, this is 10dC (50dF). In a Cherokee 180, it is 40dF. In my Twin Beech, it's 35dF. Each is different, but once you find it, you have it.
If it will not run smooth LOP, you have other problems like induction leaks or weak spark plugs or other ignition issues. ANY conforming engine with good F:A ratios and a good ignition system will run smoothly LOP--or it is not conforming.
Walter Atkinson
Advanced Pilot Seminars
I have personally run many carbed engines LOP with excellent success and repeatability. I know of several hundred others who are having the same success. Here is the issue.
A carburetor atomizes the fuel into small, medium, and large droplets. These droplets weight differing amounts and take different paths in the induction system. This results in varied F:A ratios among the cylinders. If one can get the fuel droplets VAPORIZED early in their progression, the F:A ratios will be quite even between the cylinders and the cylinders will have the same F:A ratio and therefore the same Hp output and will run smooth along the entire mixture spectrum.
One method to improve this vaporization has been to **** the throttle plate slightly to induce some turbulent airflow into the induction. This has been successful in some applications and not so successful in others. As it turns out, each engine and installation has an optimum carb temp which results in maximum vaporization and minimum heat required. Once that is discovered, simply setting that Carb Temp will result in maximum vaporization and optimum F:A ratios. As soon as that is accomplished the engine will run smoothly LOP.
How to find the optimum carb temp:
1) Set the engine monitor to the DIF function.
2) Add carb heat until the DIF is the lowest number you can get with the least amoutn of carb heat.
3) Note the Carb Temp. This same temp can now be set, winter, or summer, high or low to achieve the optimum fuel vaporization.
In a C-182, this is 10dC (50dF). In a Cherokee 180, it is 40dF. In my Twin Beech, it's 35dF. Each is different, but once you find it, you have it.
If it will not run smooth LOP, you have other problems like induction leaks or weak spark plugs or other ignition issues. ANY conforming engine with good F:A ratios and a good ignition system will run smoothly LOP--or it is not conforming.
Walter Atkinson
Advanced Pilot Seminars