Hi everyone, a newbie here, really hoping someone can help me out. I am an Electronics Engineer to trade, but this one is really start to make me question my capability. A few weeks ago my Foreman 450S suddenly refused to start. I have been through a great deal of investigation, which started by checking for a spark at the plug - but nothing when cranking. So, to cut a long story short, I have checked all the resistances in the stator windings, and in the Ignition Spark Generator coil, and all test out fine. Over the weeks I have been trying to fault-find, I have replaced the Ignition Coil, Battery, Ignition Spark Generator, but no change. My latest replacement was the Rectifier/Regulator, and there has been a change of symptom. I am now getting a spark when the start button pressed, but no sparks while the button is pressed in, and a second spare when the start button is released. The bike cranks perfectly, with no apparent starter issues. I have seen a great deal of posts around no spark issues, but as I have completed a great deal of testing and replacement of crucial components, I now feel I need some guidance from the experts. So here I am, any help would be ever-so greatly appreciated. I really mean that.

 

Welcome to the weird world of CDI ignition. Lots of people on here have had the same problem, but I have never come across a definitive answer. I would be surprised if you don't get a decent set of sparks if you use the pull start. Some say it is a dirty trigger coil. A bit of a faff to remove the alternator and find out. One thing I did find on a 350, is the neutral light circuit is connected to the CDI and gives a better spark with the bike in neutral. If this is not connected you don't seem to get a spark when starting via the electric start.

If you can't get it right, the starting technique is to press the start button in short bursts, one of those first turn or last turn sparks is going to fire the mixture, and start the engine.

Incidentally, if you suddenly loose sparks on a 450, always suspect the regulator first, for some reason the 400/450 are the only bikes that kill the spark if the regulator fails.

 

Hi merryman, thanks for the quick response. The pull start is kindoff hard to pull, it often allows a short release of the rope and then sticks, but I'll get that tonight. I have replaced the Igntion Spark Generator, and measure it at 321ohms, so all good on that front. I have assumed that the Neutral light circuit is connected to the ICM, as the Neutral Light is on, and the Starter turns. That's not to say that there is a problem between the T-off and the feed to the ICM via the 2 way connector, can check that tonight as well. I have also replaced the Ignition Coil and the Rctifier/Regulator assemblies. As mentioned above, the condition did chage after the Regulator changed, from no spars at all, to spark at Starter Button Press, and spart at Starter Buttton Release, but nothing in between.

 

Could be your new "spark generator" is too far from the flywheel, or just a dud. I had a Yamaha before Christmas that resistance tested OK for both trigger and "power generator" (exciter) coils, but in desperation, I sent the alternator to a rewinder, they found a fault in the exciter coil, fitted a new one and all is well. I would put the old trigger coil back if the fault isn't found in the neutral circuit. Looks like that red/green wire from neutral light switch is just earthed in neutral, so a good earth signal on it at the CDI, is what you need.

 

All OEM parts used so far. Did some more testing tonight, and I confirmed the pulses from the Stator (Ignition Pulse Generator) at 20Vpk (Positive Pulse, then a Negative Pulse, Pulse Width 10mS), which I think sounds about right. The pulse are a little ugly, but clean enough. The Yellow wire from one of the Stator lines is getting to the ICU, and measures approximately 10/11Vpk. The output of the ICU to the Ignition Coil is a mess. Result is a +130Vpk pulse when Start Button pressed in, then just noise around 0V while button is held in, then -130Vpk when button released. This explains why I am getting a spark at press, and then at release. So, I am fairly sure this points to the ICU. Anybody agree?

 

Thanks merryman, check the Neutral line, it's a good earth to ground.

 

"I am fairly sure this points to the ICU"

Been there, done that, and no improvement on a 350. Don't have an oscilloscope, which I assume you must have, but tried the substitution route, changed everything except stator/trigger, as that was too much trouble, cleaned up all earths I could find, even changed the starter in case it was taking too much power, nothing worked. Let us know if a new CDI works for you.

 

Now getting full spark train, don't know what I did, but it's working again (for the moment). Got a spark train, but the bike will not start. Onto the next fault!!!!