WHAT IS IT A GOOD COIL?

Hi There,
        I’ve a problem with my 02 Cali EV. It fires up no problem from cold, but as soon as the engine is mildly warm, it will not restart. e.g. Trip to the garage 1.5 miles away, filled up turns over aplenty but will not start. At the time I had a very quick check for a spark, which there was, but as I recall (I was a bit stressed at the time as I had to be somewhere important) it may not necessarily a fat blue one. After numerous attempts to restart while waiting for the RAC, I managed to get it going after about a hour with the only redeeming feature that the battery seems to be extremely healthy.

A very knowledgeable friend and auto electrician has suggested checking the coils. The ones fitted are Magneti Marelli BAE850AK. Greg Bender says the resistance on these should be primary coil 0.7-0.8 ohms and 3260-3280 ohms on the secondary coil. When removed from the bike and checked with an inexpensive multimeter, I have R/hand coil 1.2 and 3120 ohms and left hand coil 1.2 and 3140 ohms.

All these values seem low compared to other coils, and mine both seem very different to that quoted by Greg. Am I so unlucky (I often am!) to have two duff coils? Can anyone tell me what the resistance on a good BAE850AK coil should be? I understand they are very common on big Guzzi’s and Ducatis.

Alternatively, if the consensus is that my coils are reading what they should, can anyone suggest any other reason for my restarting problems. N.b. I haven’t been any distance for a while, so my problems may not be confined to a warm restart.Â
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at first reading it would appear that the coils stand a big chance of being the fault, but as in life sometimes there are other reasons, the EV coils are not known for being a troublesome item, and for both to fail at the same time ? no, when it fires up from cold check carefully (keeping your hand away from the exhaust pipes) if the coils are running very hot, if so they could be naff, have you tried chucking in some new spark plugs to see if that makes any difference ?. as it starts ok it appears that there is nothing wrong with the basic ignition system but as it then decides it dont want to come out and play again it comes back to either the coils or the spark plugs. not sure re your '02 model but my '97 Ev has a big long plastic plug on ther ECU unit under the seat, it might be worth just unpluging it (iginition off) and replugging it as I have found , on just a very few occassions ( about twice in 14 years), that riding down our pot holed holes can cause this plug to work just a bit loose.

Have you had this bike from new or has a previous owner possibly changed the coils?

In practice it is very difficult to measure very small resistances, because the slightest bit of tarnish on a connector or probe tip of the multimeter can easily add 1 or 2 Ohms. I suspect a fuelling problem like for example ECU thinks motor is still cold so is over-fueling it on the restart so it’s effectively flooding the motor, but just a wild guess. If true that suggests the problem lies with temp sensors maybe. (?)

Plus the resistance of the probe wires themselves become significant at low readings - but I think Mike might be onto something there re the temp sensor

Does play up when properly hot too?

Also. I know my carby can be a cow to start hot if the carbs are out of balance if that’s food for thought

As noted coils are difficult to check. And what shows a spark at the plug when out in the elements may not work under operating conditions. Motorcycle dealerships used to carry kit for testing them properly so you could try locally.

With a twin coil set up it seems exceedingly unlikely that they are both dead at the same time. I’d be looking elsewhere, as others here are suggesting.

With an adjustable air gap up to an inch or more! Generally a quarter inch in open air should be good enough for most practical purposes.

With a twin coil set up it seems exceedingly unlikely that they are both dead at the same time. I’d be looking elsewhere, as others here are suggesting.

Quite so!