Ignition coil testing...

[Dave T.]

I was just going through my factory manual and found something. Secondary testing of the coil says to do so through the spark plug cap.

I DISAGREE WITH THIS. If you think I'm wrong let me know. The manual says that the spark plug cap (stock) should be 10,000 ohm's + or - 15%. There is no way your going to get 7.9k ohms on the secondary side testing through the spark plug cap. Minimum 17.9k ohms with a stock cap.

As far as tolerance, you get +- 15% on the primary side, +- 20% on the secondary side and +- 15% on the spark plug cap. Testing should also be done at room temperature.

This just bugs me because when I was starting out this confused the hell out of me. I am here to ban confusion from this board... ? 8)

[gbranche]

Speaking of ignition coil testing, I tested mine this weekend, at room temperature, and the readings were all within limits. Does this mean that the coils should be OK at operating temperature? I've been having a problem with a cylinder cutting out sporadically, and it only seems to happen when the temperature gauge gets to the 12:30 to 1:00 o'clock position (i.e. just to the right of the straight-up needle position). Once I let the bike cool down again, everything is fine until the temp rises back to that range.

Initially, I suspected the TCI. I disabled the rev-limiter circuit, and that didn't solve the problem. I replaced the TCI with another unit, and that didn't solve the problem either. Searching through the forum archives led me to suspect the coils (especially considering their position just above the radiator), but they seem to be OK, at least as far as the service manual testing procedures are concerned.

I intend on cleaning all the connections later this week when I get some time to do so. (I like the CLR suggestion...) Does anybody have any other suggestions as to what I should be looking for?

Greg

[Silver_Bullet]

Greg,

In doing the resto on my machine, I found a hairline crack on one of the coils.  I too, had intermittant problems with misfire, but once coils changed, no more problem.  This crack was not easy to see, the nut stuck on the mounting stud and when I put a wrench on it, the crack opened.  I was able to get two new ones from Yamaha at about $84 each (ouch :o).

Mark

[GAJim]

I replaced mine with dyna coils for far less than that with better spark.


try e-bay

[Lucky]

You might want to do an ohms check of the pick-ups in the stator case, both cold & hot & compair the readings.  i'd tend to think they were more prone to a heat problem than the coils, considering they're in with the "hot" stator, but coils seem more likely to fail.

i believe the specs are in the book...

--Lucky