How to tell if a CDI box is bad

[pantera1975]

Do they just work or not? My 85R still dont run right mostely a hi RPM I put in my 86 motor which all ran fine and the 86 carb. It still runs the same. I'm gonna swap out the coil tonite. All thats left is the coil and CDI.

[riverrat]

85 and 86 CDI boxes are different, but I do not know if one will work with the other. The trigger/stator and timing curve might have something to do with it.
RMstator sells a coil and CDI box for $90 shipped on ebay. Definitely has more spark than stock. I also purchased an extra CDI box that I don't need, let me know if you want to buy it. Only thing is I can't guarantee it since I never tried it. It is a used Honda CDI box. $30.

[pantera1975]

What the rest of the story is... When My 85 had the original motor in it it ran the same way as it does now with the motor from my 86. I'm gonna have the 85 bottom end redone for a bigbore kit since that one was a ice racer all its life and IDK whats all been apart and cobbled in it from the past owner. My 86 motor never missed a beat when it was in the 86 frame using those electronics thats why I questioned the coil and cdi. I'm lost.


I just double check the stators on Ricks electric are the same from 85-86

[tri again]

Interesting problem.

Did you happen to swap over the wire harness too?
Questionable grounds are #1 .
I've heard of people swapping out harnesses only to admit
that their old ones were probably good.

But simply by going thru EVERY connection with the swap, they now work.

To answer your question, most folks agree that swapping with a
known working unit (cdi) is the only real way to see if they work.

there's a funny (scary) website called sunLpartsonline.com that
has cdi units from 69 cents on up.

[riverrat]

Well the CDI box isn't, I don't know if there is any difference between them other than just the plug connector. Probably not.
For the price, it's always good to have extra electronics around, since when these things go, it takes time to get them again.

[pantera1975]

Here are the wires and coil I just took off. The wires were really fused to the coil almost like the one was soldiered to the terminal. The previous owner hooked his tether cord in to the black yellow wire and the other wire from the tether was to a ground. Im pretty sure that's how it was but when I was pulling on the coil leads one of the 2 red wires pulled out from somewhere. The tether switch has tape around it to keep it pushed in I never tried it to see if it works. At some point the CDI was replaced because he told me it was and there is one in a box of parts that is used. When I swapped motors I just unplugged the stator lead and hooked it up to the other motor. I need to replace the female spades for the coil hook up does it matter if I use heavier wire and butt connectors to lengthen them out for resistance? Like I said the 86 motor in the 86 frame ran perfect. Ill check the grounds. I got a pro armor killswitch for my 86 rebuild. On a 86 what and where should I hook up the 2 wires.

[pantera1975]

The other thing I noticed is last summer the original spark plug boot ripped apart when I took it off so I replaced it and it dont get snug at all on the coil wire

[riverrat]

I am not sure, but the fact that your wires were baked to the coil, that is a bad sign of something. You could have a weak coil with a lot of resistance. The manual gives you ways of testing the coil, and the trigger, and the stator. Not sure about the CDI box. Get the right boot too. How I trouble shoot stuff is if I see something wrong, I fix that thing, and it always brings me to the next problem. If it pops in your head that something ain't right, then it ain't, that's your brain trying to tell you something. :D

[pantera1975]

http://www.weddemotorsports.com/servlet/the-579/Genuine-NGK-Spark-Plug/Detail Here is the boot I have been using. Could you put up a link for the one you think i should be using? I'm gonna fix the wire tonight ans try my coil from my 86then everything to do with it running is from my 86 except the harness and cdi box. As far as the spark plug boot staying on the wire off the coil is all hogged out from taking off the boot without unscrewing it.

[riverrat]

That boot seems fine except that you said it isn't snug on the wire. That one may be for a different gauge wire. Not sure where to get the right one. You could use a rubber hose as a sleeve to make it snug. You definately dont want movement in there, if it isn't the problem now, it will be later.

[pantera1975]

I swapped out the coils and fixed the wires. I started it and could tell a difference at idle something was better. Took it out in my 2/3 acre yard in town and its better then took off the airbox lid and wow it really revs. IDK remember the jetting I have in there now its rich trhere gotta be a 50 slow jet in there and a 152 main or a 155. In the summer I ran a 45 and a 148 @ 40-1. Thanks for the help. Ill check out the RM stator

[tri again]

Not sure where your air comes from.
Some suck thru the frame and mice (and mud bees) just love to build nests.

Just for info,
I believe that beatrice cycle has kits that will make different cdi units fit
different applications.

Nice to hear it runs and nice the airbox lid/restriction made a magical difference.