Some may have at the end of the 70s the reason for it is to allow the timing to be advanced when under high vacuum conditions. (near no load and at many speeds) At idle the vacuum can be high but the centrifugal advance is retarded to near the initial static timing. (IIRC all distributor systems from the early 50s on up have centrifugal advance under the breaker plate) Then when the engine is increased in speed (but under little load) the centrifugal advance and the centrifugal both advance the spark. this allows better fuel consumption and still avoids spark knock at high vacuum low load conditions. When the governor opens the vacuum advance pulls the timing back to load condition to, again, avoid knock. The centrifugal advance is only RPM controlled, so the advance does change with engine speed under loaded, or partially loaded conditions. Early tractors were designed without consideration to pollution, or smooth running. Magnetos used in that era had no advance or other timing mechanism other than the impulse coupling delay to get them running without breaking the cranking persons arm. After starting they ran poorly at idle because the timing was set at full throttle full load timing. Jim
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Today's Featured Article - Restoration Story: Fordson Major - by Anthony West. George bought his Fordson Major from a an implement sale about 18 years ago for £200.00 (UK). There is no known history regarding its origins or what service it had done, but the following work was undertaken alone to bring it up to show standard. From the engine number, it was found that this Major was produced late 1946. It was almost complete but had various parts that would definitely need replacing.
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