Odd little engine issue ?
Discussion
I have noticed that sometimes if I stop the engine then turn the ignition back on, when I turn the ignition off there is a slight 'huff' as the engine seems to turn over slightly. It's not consistant but definately happens regularly when doing the above.
I have thought that perhaps a spark occurs (why?) which ignites fuel remains in one cylinder, or perphaps it's a release of compression in a cylinder but can't understand what could be the cause. Presumeabley it must be caused by an electrical issue as it only happens as the ignition is turned off.
Can't get my head around it... any ideas's please share as it's totally
me.
I have thought that perhaps a spark occurs (why?) which ignites fuel remains in one cylinder, or perphaps it's a release of compression in a cylinder but can't understand what could be the cause. Presumeabley it must be caused by an electrical issue as it only happens as the ignition is turned off.
Can't get my head around it... any ideas's please share as it's totally
me. The contact breakers in the distributor are simply a switch that turns on and off the low tension circuit in the coil. The coil produces a high tension spark via the king lead which gets routed by the rotor arm to the relevant plug lead and plug.
When the engine stops, there is a good chance that the contact breakers will be closed (dwell angle is the relative time that the CB points are open/closed) so the ignition acts like the contact breaker switch and causes a spark.
There is a good probability that the spark will be routed to the cylinder that is full of warm fuel/air mix and is ready to fire (the inlet valve may be open a bit causing the noise), remember the sequence suck, squeeze, bang and blow.
Off topic from the OP but I was impressed to see on Wartime Farm (BBC) the other day that one make of 1930s tractor used a shotgun cartridge (without pellets) to start the engine. He referred to the hammer used as the ignition key ;-).
Russ
When the engine stops, there is a good chance that the contact breakers will be closed (dwell angle is the relative time that the CB points are open/closed) so the ignition acts like the contact breaker switch and causes a spark.
There is a good probability that the spark will be routed to the cylinder that is full of warm fuel/air mix and is ready to fire (the inlet valve may be open a bit causing the noise), remember the sequence suck, squeeze, bang and blow.
Off topic from the OP but I was impressed to see on Wartime Farm (BBC) the other day that one make of 1930s tractor used a shotgun cartridge (without pellets) to start the engine. He referred to the hammer used as the ignition key ;-).
Russ
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