OK, let's flog this one to death.... Of what I know about engines..... 1) It is a proven fact that leaner mixtures burn hotter. That is why modern engines use EGR - to COOL and DILUTE the combustion to reduce peak temperatures. This results in less formation of NOx. 2) Retarded timing will also make an engine run hotter. Just look in any old auto repair manual (like an OLD Motor's or Chilton'e). One of the listed leading causes of over heating is retarded timing followed by mixture too lean. 3) Fuel is introduced into the combustion chamber as a VAPOR, and should therefore have minimal cooling effect. 3) OCTANE! Most people do not know what octane is or what its effect is. so.... a) Octane is a comparison to what was once designated as the "ideal" motor fuel....Isooctane. b) Octane is determined by flash point and rate of burn when ignited as well as Reid vapor pressure. Lower octanes have lower flash points and faster burn. In view of this, I would say that octane most certainly DOES have an effect on run-on!
The bottom line is that you still need fuel mixture, compression, and an ignition source for an engine to run or run on. Given that the compression will be present after the engine is turned off, and that fuel mixture will also still be available, the source of ignition comes into question. Given that after the switch is turned off, the engine parts are still moving, and are still hot, I would say that my conclusions are as follows:
1) Reducing the idle setting would also reduce the likelihood of running on. 2) Higher octane fuel would also reduce running on due to the higher flash point. 3) Timing is irrelevant. 4) Reducing operating temperature should also have an effect on running on.
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Today's Featured Article - Earthmaster Project Progress Just a little update on my Earthmaster......it's back from the dead! I pulled the head, and soaked the stuck valves with mystery oil overnight, re-installed the head, and bingo, the compression returned. But alas, my carb foiled me again, it would fire a second then flood out. After numerous dead ends for a replacement carb, I went to work fixing mine.I soldered new floats on the float arm, they came from an old motorcycle carb, replaced the packing on the throttle shaft with o-rings, cut new ga
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