I have a 1993 Trail Boss 250 that does not spark, and I don't understand why. The spark plug does not spark, but if I take a volt meter and put one end in the socket and put the other end to the chassis, it sparks strongly and consistently. Anyone know what I can do to fix it?
LutzyGT500
No spark, but strong everywhere
You are lucky that you didn't ruin the meter.
So how far will the spark jump? 1/4 inch? If it won't jump a 1/4 of an inch in uncompressed air, it will never jump a .028 gap in the cylinder under compression.
So how far will the spark jump? 1/4 inch? If it won't jump a 1/4 of an inch in uncompressed air, it will never jump a .028 gap in the cylinder under compression.
Say you got a weak coil. That voltage should of burnt out your meter and since you've tried multiple plugs I'd say pretty safe bet coils shot. What's the resistance on the coil. Another thing to check first is you don't have a grounded kill wire
Well, two things that are now known is that the pulse coil is working and the kill switch is not causing a loss of spark.
Presumed to be working is the CDI unit - it is discharging into the coil and the coil is producing a spark.
Not known is: the condition of the grounding of the engine to the frame, the grounding of the coil to the frame, the functionality of the coil and CDI charging coil. The coil may be at fault if the CDI unit is discharging an approximate 100 volt peak voltage spike into the coil and the coil is not raising the voltage of the 100v spike to appx 30,000 to 40,000 volts. The charging coil may not be generating the necessary appx. 45 volts that the CDI unit amplifies and rectifies into DC to charge the capacitor to the required appx. 100vdc.
I suggest you do one of two things; either buy or borrow a meter with a peak voltage function to measure the output of the charging coil, CDI unit and primary coil or start throwing parts at it. If you decide to start throwing parts at it, start with a stator, they have the highest failure rate or try a new primary coil as they are relatively cheap and easier to replace.
Presumed to be working is the CDI unit - it is discharging into the coil and the coil is producing a spark.
Not known is: the condition of the grounding of the engine to the frame, the grounding of the coil to the frame, the functionality of the coil and CDI charging coil. The coil may be at fault if the CDI unit is discharging an approximate 100 volt peak voltage spike into the coil and the coil is not raising the voltage of the 100v spike to appx 30,000 to 40,000 volts. The charging coil may not be generating the necessary appx. 45 volts that the CDI unit amplifies and rectifies into DC to charge the capacitor to the required appx. 100vdc.
I suggest you do one of two things; either buy or borrow a meter with a peak voltage function to measure the output of the charging coil, CDI unit and primary coil or start throwing parts at it. If you decide to start throwing parts at it, start with a stator, they have the highest failure rate or try a new primary coil as they are relatively cheap and easier to replace.
Not quite true - if the available energy is strong enough to ionize the air, the spark will occur even if the plug is a 1/4 inch away from the engine, but the engine (which is mounted on rubber cushions) needs to be connected to the frame to get a spark to the engine. I will test to the frame before testing to the engine because the link that grounds the engine will fail more frequently than the connection of the coil to ground. A good ignition system will jump about an inch and a racing ignition may jump several inches. Top fuel drag racers use MSD ignition magnetos that may throw a spark several feet.
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