Does my coil work?
speedyxjs - 15/9/09 at 07:02 PM
Sorted out my earlier problem (rookie error 
) but now want to check i have spark.
Due to the wierd design of the engine, i dont think i can fit one of those plug tester things down so thought id check the coil is working.
I can get the full 12.5 volts if i connect the multimeter to the +ve on the coil and the earth but if i connect it to the +ve and the -ve on the coil,
i get a much lower reading. Is this right?
I appreciate all the help im getting on these stupid questions and you will hopefully be rewarded by a start up video at the weekend or if i cant get
it sorted, next weekend 
locoboy - 15/9/09 at 07:05 PM
I dont know,
Are you pregnant?
GeorgeM - 15/9/09 at 07:09 PM
just saw that & thought the same 
Fozzie - 15/9/09 at 07:10 PM
quote:
Originally posted by locoboy
I dont know,
Are you pregnant?
Damn!..... I was gonna say that! 
Fozzie
flak monkey - 15/9/09 at 07:13 PM
When there is a distributor trigger event (points opening or hall sensor trigger) the coil is turned off by disconnecting the negative.
The time the points are closed is the dwell time (sometimes measured as an angle as well) and this is what determines the amount of charge in the
coil.
A coil is 2 coils of wire, one long and one short. When the coil is turned off the field collapses in the small coil and induced a current in the
large coil giving you a high voltage output to the spark plug.
So in answer to your question, probably 
As long as your distributor trigger works (whichever it is) and the coils in the coil are ok (one should check a high resistance (the big coil
measured between the ht connection and the pos terminal) and the other low resistance (the small coil - measured between the pos and neg terminals)
what those specific resistances are depends on the coil.
David
speedyxjs - 15/9/09 at 07:32 PM
quote:
Originally posted by locoboy
I dont know,
Are you pregnant?
I think im missing something?
Flak - There are no points. Its all controlled by a little box
flak monkey - 15/9/09 at 07:41 PM
The little black box will be an amp for the coil sensor. Still works the same way as points, switches the negative side of the coil on and off to time
the sparks accordingly.
speedyxjs - 15/9/09 at 07:44 PM
quote:
Originally posted by flak monkey
The little black box will be an amp for the coil sensor. Still works the same way as points, switches the negative side of the coil on and off to time
the sparks accordingly.
Great cheers
flak monkey - 15/9/09 at 07:47 PM
I meant dizzy sensor. Lol
Really should proof read posts.
big-vee-twin - 15/9/09 at 08:16 PM
I have engine with the spark plugs down in the casting so can't use a tester.
The way I checked my coil was to use a spare spark plug leave all the plugs in the engine, disconnect an ignition lead push the spare plug into it,
touch the plug to earth tun over the engine. If it sparks your good to go.
Danozeman - 15/9/09 at 08:56 PM
quote:
The way I checked my coil was to use a spare spark plug leave all the plugs in the engine, disconnect an ignition lead push the spare plug into it,
touch the plug to earth tun over the engine. If it sparks your good to go.
Id go with that, Muchos easier that this testing mallarky.
02GF74 - 16/9/09 at 07:19 AM
quote:
Originally posted by speedyxjs
I can get the full 12.5 volts if i connect the multimeter to the +ve on the coil and the earth but if i connect it to the +ve and the -ve on the coil,
i get a much lower reading. Is this right?
what is the voltage for thius "much lower reading"?
as ^^^ says, the -ve is the "switched to earth" terminal, so depending on the position of the sensor, either the amp is switching the coil
or not.
if switced on, you would expcet to see almost the full batery voltage, less maybe 0.2 V or if not switched, a much lower voltage across the coil.
if you loosen the distributor or put it in such a positon that you can turn the rotor (assuming there is a mechanical advance) enough to trigger the
amp, you would see the voltage go between both extremes.
be carful when doing this as the coil will want to product a spark that will want to go somewhere, ideally not through you!!