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Coil Really Hot

N

Nathan Stanley

Just got it firing!
Joined
May 10, 2020
Messages
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4
Location
Las Vegas
I decided to post this here rather than the vintage section because I assume ignition coils are pretty widespread.
The bike is a ‘75 850T. I noticed that with the ignition turned on with the key, engine not running, that the coil for the right cylinder is getting very hot, and heating up the frame tube it is mounted on. The coil is almost too hot to touch. The left cylinder coil is not much warmer than ambient. Both cylinders were running(mostly) before tearing into some project work, but the right cylinder was not firing at low rpm. I made a timing adjustment, and corrected the valve clearances. I assume these were the problems, and it isn’t put back together enough to try firing it up yet. I traced all the wiring in the vicinity and everything looks to be attached properly with the correct wires going to the correct terminals.
Any ideas on why 1 coil gets really hot?
Thanks!
 
With the key on and points closed current is running through the coil. The longer this condition lasts, the hotter the coil will become. If both sets of points were closed when you checked this, then the right coil probably should be replaced. A good replacement can be found here: mgcycle.com/index.php?main_page=product_info&cPath=37_157&products_id=603
 
That makes sense why the other coil wasn’t also hot. I checked the resistance and got 3.3 ohms. They’re the original coils, so they’re probably due for replacement anyway.
 
That's not that far from stock resistance , don't spend money for nothing . Try it first after you've made the other adjustments :).
Peter
 
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