1993 Yamaha Big Bear 350 ignition issue

[Mellansc]

Hello all,

 

First post here, I've been searching these posts for a similar issue and have found some close but no real answers yet. So my Big Bear has an ignition issue ran great till last year then quit. A shop changed the coil and CDI on it and it worked for about an hour and now its back to the same issue, I just changes the stator and pick up but that did not fix the problem either! So now basically all the parts have been changed. So what it does and its the part that's confusing me a lot is when I crank it over with the electric start there's no spark but if I pull it over by hand there's a good spark?????? And if I crank it over with the electric start and at the same time slide the kill switch from on to off it will spark once then from off to on it will spark about 3-4 times. I'm lead to think it's the CDI except it works when I pull it over?

 

Looking for ideas here.

 

Scott

[Curtis Underwood]

 To start with sounds like you have either a issue with a switch or wiring. The CDI unit is powered by the CDI magneto (it has no battery power running to it). So if it is running correctly from pull start and not from electric start then  you could have a bad start relay, bad neutral relay, bad wiring, bad switch, Bad connection in a connector or Lose ground wire could also cause this.
If you have a voltage meter hook red lead to positive on battery and hook black lead to B/W wire coming from kill switch. If at any time this shows 12 volts then the ignition circuit is killed. If it shows 12 volts during electric start then that means the kill circuit is grounded. This test will tell you when the kill circuit is not allowing it to fire.` 
  Look at the neutral light. Does it stay on when you mash the starter Pushbutton? This sends a ground to the CDU unit that has to be grounded for the start circuit to energize, if the neutral light is going out the your losing ground to the CDI. I had this problem and it was a bad relay, contacts in the relay were made all the time allowing the starter to turn over in any gear but it would not fire unless it was in neutral.
  The kill switch is bad about being intermittent and the contacts when closed kill the machine (this handle bar switch cause more problems then most of the other wiring put together). Disconnecting this to take that out of the circuit(either cut the b/w lead or use a tool to remove the lead from the plug, you will have to hook this back up after troubleshooting). It should start and run with it disconnected if it is this switch causing the problem. Your start pushbutton and kill switch is in the same assembly on the handle bar, pushing the button could be causing the kill contacts to make and not allowing the machine to fire..
 The issue sounds like the cdi is grounding on its kill circuit when the starting circuit is engaged. Most all the wiring diagrams are about the same except for a few things, like reversing relay 1988 has it but most don't, this one is for a 1988 Yamaha Big bear. Highlighted in yellow is the black wire which is ground. Red is the R/W wire witch is comes from brown 12+volt. The green highlighted wire B/W is the kill circuit, if this is grounded at any time, then the machine will not fire.

[Mellansc]

Wow thanks Curtis!  This is very helpful. I pulled the wiring out today and checked all wires and connectors, found nothing suspicious there. I’ll try your tests and let you know what I find. If I cut the kill circuit wire to the CD I would that confirm something wrong further down the circuit?

 

scott

[Curtis Underwood]

Yes Scott if you cut the B/W wire on that kill circuit and it runs and starts under electric start it would confirm that the switch assembly is bad causing the problem. The way you described this problem it has to be in the wiring or possibly a cross feed during electric start.
The Main Switch has two functions one is to supply 12+ power to the system when the switch is on and the other is to ground the kill circuit when the switch is off. The way this starting circuit works is the when the Main switch  is turned on it opens the the connection to the kill circuit and send 12+ to the Brown wire which supplies power to the relays and lights.
 All three control relays Start circuit, Neutral safety, and Reverse relay have 12+ applied to one side of their relay coils as long as the main switch is on. This is a European style electrical system and uses a ground to control the on/off of the relays. The Start circuit cut off relay has 12+ supplied to it's coil as long as the main switch is on then when the start push button is pressed it connects the ground to the other side of the relay coil which energizes the relay and the contact in the start cut off relay closes sending  12+ to the starter relay which has ground to one side of the relay coil (just the opposite of what is used on the control relays).  They did this so that there is no +12 Volt on the handle bar and I think this was a safety issue.
 Since ground is used as the control it causes a lot of places where the kill circuit could be grounded.
From What I have been able to find this 1988 diagram is the same as the 1993 using 3 relays. The blue relay (Reverse Relay)is a Normally close forced open where the two other relays(Neutral safety and start cut off) is normally open forced closed.

[Mellansc]

Ok so I tried all those tests and what I found is the kill switches are working ok. I do see a very low MV reading when I tried the electric start. I also tried cutting those kill wires to the CDI but still same results. 

[Curtis Underwood]

  That MV reading do you have the reading in both electric start and while pull starting? If not in pull start then this is going to be a sensitivity problem in the CDI.  But this make it sound like you have a bad ground somewhere. The only thing in common is the grounds.  If a ground is loose near the CDI and you start the engine with electric starter it could put a load on the ground wires causing the ground which is natural low to go higher and interfere with the CDI. This is the only thing I can  think of that could be causing the problem. 
Here is what I would do.
With everything hooked back up as it was when you started.
Ohm the black wire on at the CDI unit and make sure it ohms is 0 ohms to negative at the battery and not some high number(you can do this by stripping back a little of the insulation then later you can tape it back when your have the ATV fixed). Then I would run a temporary ground from battery negative to the black wire where you stripped it.  If it starts you have a bad ground connection somewhere. If it does not start then I would have to have the unit in front of me to see what is going on.
 I am a senior electronics technician and would have to run some tests that require specialized equipment. If it does not start grounding that black wire at the CDI then it will most likely be the CDI has become sensitive to electrical interference. Some CDIs have a micro chip in it that control the firing, this microchip can become sensitive. Electric motors will generate electrical interference.

The only things in common between electric start and pull start is the B/W kill wire and the grounds. A bad ground or one with a higher resistance could allow it to start with pull start and during electric start open up and not give a ground to the CDI.