Re: SPARK PROBLEMS, I dare you to explain this one!
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Posted by Paul Fox on June 21, 1998 at 04:15:48:
In Reply to: SPARK PROBLEMS, I dare you to explain this one! posted by Joe Brown on June 20, 1998 at 18:45:06:
: Farmall Cub 48. New coil in mag,condenser, points,cap,rotor,wires,plugs and carb, timed on the money. This thing just keeps running rough. I pulled the wire from the coil while it was running to look at the spark. If I pull the wire out till I have a 1/2" spark jumping from the coil to the wire the engine runs smooth as silk. If I move the wire into the coil and make connection it runs rough again. I tried widening the spark gap but this didn't help. I've been told I need to add a resistor on my plugs. Can anyone back this up and or explain to me whats happening. Thanks in advance. Joe: I'm applying basic electrical theory here, and I can't guarantee it's valid, but here goes: Ohm's Law states that Voltage=Current x Resistance (E=IxR). My theory is that the mag is putting out a relatively constant current. When you pull the wire and introduce an air gap, you've essentially increased the resistance. With current constant and resistance increased, the voltage goes up, hence a hotter spark at the plug. This might compensate for a weak plug or an over-rich mixture by creating a hotter spark. I'd be interested to know if others think I'm on the right track here.
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