coil testing

1986 xj700 maxin X Got a weak spark both coils both plugs. No ohms in secondary side of coil. Even across both spark plug wires. Since voltage is induced from primary not sure why there would be any ohms any where across secondary. when running grounded out thru spark plug. Losing 2 volts from battery to coils, still over 10 volts. starts well but runs terrible. Could both coils be bad. probably original, only 12k on bike.

 

@vmax man ,

Yes, there should be connectivity (and therefore measurable resistance) on the secondary side just like the primary side.

I've had one that did not have measurable resistance on the secondary side but still (sort of) worked. The likely explanation being that there is a discontinuity in the coil wire somewhere such that resistance cannot be measured, but the discontinuity gets jumped by a spark the same way that the plugs do.

 

Ignition coil testing and general nerd-fest: https://www.xjbikes.com/forums/threads/how-to-test-ignition-coils-and-plug-caps.130696/

 

Hi Dan No matter what I do never got any ohm's on secondary both coils. Could they both be bad doing the same thing. I understand the jumping of high volts, over a discontinunity but both coil puzzle me, but they are original. They have a light blue and inconsistent spark. Want to make sure before I make a purchase. Will check TCI yet.

 

Sure, it's possible. They are going on 40 years old, after all.

How confident are you in your DMM skills? If it was me, pilot error is always an option on the table.

 

Been using my Fluke meter most of my life. What do you suggest, I'll do it. Just don't want to buy coils and find out it's something else. I hate trial and error, on repairs

 

Sometimes new DMM users struggle with the concept of setting ranges and that sort of thing - no big deal, they just need some training. Doesn't sound like that is the case in your situation, so that's good.

I don't know if an intermittent spark would point to a TCI failure - I'll leave that to more knowledgeable people (@Rooster53 ??). When I've experienced TCI failure it was a case of no spark on one coil.

What about your battery? The 700's use a bigger battery. I had one with a wimpy battery that caused me problems. Replacing it with a fresh and proper size battery helped a lot.

I think for now if the coils are testing bad, then they are probably the most likely suspect.

Are you testing with plug caps on or off?

 

Sounds a lot like a carb issue, you mentioned in your first post here that the carbs were leaking, which is usually a sign of needing serviced

So, that said more information is always good.

Have you serviced the carbs and if so to what extent?

Anything else like new plugs, valves checked, or compression test?

And that is a good question, along with when you say you have done something like "using my Fluke meter" be more specific - like yes, checked with spark plug caps removed and meter connected from one coil wire to the other with the meter set to auto range, or meter set to 200K scale. Spark plug caps also all checked within spec per the FSM, or if your not sure of the spec give the exact numbers - otherwise we just have to guess what you might be doing.

And the last thing to mention is it is best to keep your specific bike issue in one thread so all is easily reviewable and remembered

 

I pulled the wires right out of the coil. Wires are good, but testing the peckers down inside the coil nothing, both coils. Have to realize that both coils can go bad. Keep yah posted. Thx

 

Well that's interesting, unless the 1986 xj700 X is different the plug wires do not come out of the coil without major surgery as they are molded in there

 

That's the scary thing, Im just not sure what the people before me did. The new ones I have coming look molded right in there. Wire colors are correct, mounting distance is correct, and of course with parts Made in Japan! I'll keep yah posted. By the way you asked about carb float setting. I removed them from the bike, did a wet setting on bench. Plugged in 4 hoses with 90 degree elbow, in drain hole. Measured the tab on float with Mike, wrote it down and went from there. Only put 2 bolts in bowl, leveled every time, after a while I got really good at it.

 

I'm going to change both coils on this maxim X any suggestions where to purchase. Do Dyna coils work??? Looks like I need to modify bracket to secure them, if I go Dyna.