No Spark at Plugs - Checking a 12 Volt Coil?

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rby1234
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No Spark at Plugs - Checking a 12 Volt Coil?

#1

Post by rby1234 » Mon Jan 21, 2013 6:54 am

I'm sure this is covered somewhere (but I couldn't find it in simple language that I could understand). Is there a way to check to see if my "rectangular" 12 volt coil is bad? My electric start Panhead just stopped running this weekend and after getting a tow home, I did some checking and found the following: (1) battery is in excellent shape and is always on a trickle charger (2) carburator recently rebuilt and fuel delivery is good (3) there is no spark at the plugs (4) there is no spark, or power at the points - obviously with the ignition on (5) all wiring looks good and there is good continuity with the wire which goes from the circuit breaker (points) to the coil (6) with the ignition on, got plenty of juice at the hot side of the coil (7) plug wires and plugs look fine. I don't know what the terms primary and secondary coil refers to; when Iooking at the coil, got two spark plug wires coming out the top (front cyclinder goes to the rear of the coil) and two terminals, one on each side of the coil (ignition switch hot lead goes to rear of coil). I did read the knowledge base article on coil wiring (which says it shouldn't make a big difference how the two terminal wires are connected) but haven't tried the other wiring yet. Is there any tests I can do with an ohm meter or something to confirm this coil is bad (or just buy another coil)? Would appreciate any help.



58flh
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Re: No Spark at Plugs - Checking a 12 Volt Coil?

#2

Post by 58flh » Mon Jan 21, 2013 12:47 pm

Check with volt meter if you have 12V at the points with ig. on!--If yes you may have a bad CONDENSOR!----RICHIE---Always check the Easy things first!,-if you change cond. change your points to!---Richie 8) I reread your post & you checked for voltage at the points !--Next obvious check is keyswitch!--If you had the dash off recently sometimes overtightening can cause shorts!--If you didnt have the dash off -Remove it & check all the connections!-(look for loose or GREEN corroded connections. Give them a good tug!-Also check terminal board for bad or disconnected wires!. MAKE-SURE your GROUNDS are GOOD!--ADD another ground to it!--it wont hurt anything & your covered incase the 1-comes loose!-(I run 3 grounds)& always got home in that dept..Now check all wires running close to heat sources & grounding or burning themselves to the source!.--Last but not least!--CHECK your TAILIGHT!---IF its old it can ground out & you will not start!---If you have a 65, check the solenoid for starter.---Hope this helps you it sds like alot but you can do it thoroly in 2-3hrs.--Go for the Obvious first!-Tailight, terminalboard,& wires by heat sources!---RICHIE

58flh
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Re: No Spark at Plugs - Checking a 12 Volt Coil?

#3

Post by 58flh » Mon Jan 21, 2013 1:30 pm

Dont spend money on a coil just yet!,--usually when a coil goes bad --it warms-up first then you get erattic firing!--When you shut it down & the coil cools to ambient temp. The bike will start-up & when it gets hot its the same misfiring again!---Inspect your coil for any cracks!--Try a known good coil in its place & see how she behaves. If it does to turnout to be the coil ,the VT-coils are hit & miss at best! & they dont bolt-up correctly -(they run loose when tightened-up)-you have to do some modification to holdem correctly!--If a coil is indeed needed get a QUALITY one!-DYNA COILS come to mind!--They make them for ELEC.IG. & POINTS IG. You want a 4ohm or higher for points.---The way your bike just stopped dead really leads me to believe you have a short somewhere!,(but strager things have happened!)----RICHIE 8)

blewcrab
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Re: No Spark at Plugs - Checking a 12 Volt Coil?

#4

Post by blewcrab » Mon Jan 21, 2013 3:11 pm

you could run a test wire from the batt+ to the coil...then see if u got spark...if u get spark the problem is around the ignition switch wiring...it aint nothing but a thing u will figure it out !

rby1234
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Re: No Spark at Plugs - Checking a 12 Volt Coil?

#5

Post by rby1234 » Mon Jan 21, 2013 3:45 pm

Thanks Guys, I'll keep looking for bad connections & will try the jumper to the coil. I did check the condenser and still had no juice at the points. Thanks for the good advice regarding coils!

Cotten
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Re: No Spark at Plugs - Checking a 12 Volt Coil?

#6

Post by Cotten » Mon Jan 21, 2013 6:07 pm

rby1234!

I prefer the method described on pg.400 of Palmer's,
although it requires a timer on the bench.

For a short cut, I turn the lights down low, kick through until the points are just about to open, and then open them manually with something non-conductive like a pencil, to look for a spark.
If you get a shock opening with your bare finger, that's a sign its good too.

Condensors are something that I always replaced arbitrarily.
(After all, that's retail sales).

....Cotten

Huck
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Re: No Spark at Plugs - Checking a 12 Volt Coil?

#7

Post by Huck » Mon Jan 21, 2013 8:32 pm

In my younger days I’d grab the end of the plug wire to test. I found as I’ve gotten older it made me dribble a bit on the good ones. I’ve therefore stopped this practice, for the most part…

rby1234
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Re: No Spark at Plugs - Checking a 12 Volt Coil?

#8

Post by rby1234 » Tue Jan 22, 2013 2:06 am

By the way, where is the terminal board generally located?

58flh
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Re: No Spark at Plugs - Checking a 12 Volt Coil?

#9

Post by 58flh » Tue Jan 22, 2013 1:19 pm

RBY---Theres 1-plate behind the light & 1-behind the coil,& dont forget your KEYSWITH WIRING & TAILIGHT!---Richie

rby1234
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Re: No Spark at Plugs - Checking a 12 Volt Coil?

#10

Post by rby1234 » Tue Jan 22, 2013 4:11 pm

Thanks. I'm confused about one thing. If I was to bench test the coil by connecting 12 volts to one of the terminals, wouldn't I be showing 12 volts on the other terminal? And if not, wouldn't the coil be bad?

58flh
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Re: No Spark at Plugs - Checking a 12 Volt Coil?

#11

Post by 58flh » Thu Jan 24, 2013 1:32 pm

RBY---You can test the continuity by hooking both term. up in your multimeter!--But you will have to supply 6 or 12volts to it & run a sparkplug cable,--Olny 1-problem with that if you get a spark ,it doesent mean the coil is good!--They screw up when they get hot!---The best way is to jumper it from the +side of battery & if it works --its probably good to go --You have a short somewhere that needs to be found!-look around-(wires by heatsources & steering head as they are always moving & can break if old!)--look for the GREEN - ROT at the terminals!--Pull-on the wires & solder-up any ones that you see are not up to par!--I would start at keyswitch with the V-meter & work from there!---A little patiencs goes along way here!.----Also if you change-out any HOT wires that go to keyswitch or regulater,-(remember to polarize the genny!)--a quick flash from +batt. to A-terminal-or-ARMATURE on genny is all it takes!--Good-luck----RICHIE 8)

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