Coil differences...

Sorry I did a search and came up with a thousand choices.
What if any difference is there between Red Motoplat coils with red plug lead vs black plug lead?

a diode

http://www.uk-motoplat.com/testing.htm

read the coil part at the bottom

Thank You!

Black spark plug lead coil. This type has no diode in the coil.
Red spark plug lead coil. This type has a diode in the coil

The black wire coil can only be used with the early stators that have the diode symbol on the stator. The red wire coil can be used with stators that have the diode and do not have the diode in them.

Marty

This is contrary to the situation I have... My bike is a 1980 WR 390 spark is weak IMO. It has the red plug lead on the coil. I called a buddy and asked if he had a red coil I could borrow to try. He did and I have it... His bike is an 86 which had the black plug wire with a red coil.

Which is correct?

I depends on your magneto stator. If your stator has the diode sign then you can use either coil.

If your 1980 390WR still uses the original 139mm diameter motoplat magneto then the red lead coil was used by the factory. But if I remember correctly that stator also had the diode so you could use either black or red lead motoplat coils.

If you are not sure which coil to use you can always play it safe and use the red lead coil no matter what motoplat mag you have.

Marty

Thanks Marty...

the red wire coil switched to black wire in like 85 but is same characteristics as red wire. black wire means real old, not to be confused with later 80s black wire....clear?

Joe can you explain why you can't use the late 80's black lead coil?

Marty

love it

new black wire is same as red wire!

as I recall the ones with the diode are marked as such

Well I did some testing on the coil that I borrowed from my buddy... Using the UK Motoplat repair site for specs the coil tested good across the spade terminals but the plug lead to metal bracket registered open circuit...
I pulled the spark plug cap off and tested direct to the wire and it checks as good according to specs. I'll pick up a non-resistor cap before I try it on my bike and give it back to my buddy with a new cap.

... Unless it makes my bike have good spark... then I'm keeping it!

If you have any trouble finding a waterproof, non-resistor cap with the center screw post, try a Google search for "R90 & skipsoldbikes". He still has them for $5 ea., free shipping.

(I haven't been able to post a link in my messages - there must be some trick to it... If anyone can enlighten me please send me a PM. )

Ok then if that is the case then... if the stator has NO diode then you must use a coil with the diode regardless if it is black or red lead. If the stator does have a diode then you can use a coil with or without the diode no matter if it has red or black leads.

Marty

OK thanks for the replies guys...
Something really strange... If I check plug lead to coil bracket without the plug cap I get a 5K reading which is what it is supposed to be. If I check it with the cap installed I get an open circuit reading. Makes me want to say the cap is bad.
However if I check the cap alone I get a 1-3 Ohm reading which IMO says the cap is good.
I have two new caps ordered anyway but this is getting confusing.

I am not a dunce...
I am a past ASE certified Master Auto Tech and a past Alfa Romeo Certified Master Tech. I specialized in electronic engine controls and Fuel Injection. I know my way around a DVOM and old school oscilloscope better than most but this is not making sense!

Have you snipped off about 1/2" of the end of the spark plug wire to be sure the cap is making contact with fresh copper wire strands? Sometimes the very end of the wire gets corrosion and the same for the spark plug cap. Probably best to have a new cap anyway.

Marty

I don't want to skip this one since it is not mine but the threaded stud that goes into the wire is longer than the probe on my meter and that gets reading.
Going to pick up a couple caps in a bit I'll see what happens.

OK now with a new cap I get the proper reading...

I had a motoplat repaired by www.uk-motoplat.com, the 72 125 had a very weak spark and would only bump start. He did a good job and it now has a nice big spark, was reasonably priced as well.