14 YZ450F - non-starting issue, ignition system

60h on bike, I just finished cleaned the fuel injector and fuel filter before the last ride.  Re-installed both, bike started right up, hot starting seemed to improve.  Aside from that, and an install of a Baja Designs Squadron plug'n'play headlight, the ignition system hasn't been touched since I put in a different map when the bike was new.


Got out for an actual ride, bike died about a mile from the truck.  I look down to see the pipe has melted the power cable for the fuel pump (IMS tank, cable routing is funky).  I wrap it in electrical tape, secure it elsewhere, and move on.  


After a couple more stops and starts, the bike won't start.  I can smell gas, it has compression.  I re-seat all the connectors and it fires up, with some hesitation.  For the rest of the ride it seems to start OK.


Now, back at home, complete non-start.  Choke in/out, throttle open a little, closed, whatever.  Nothing.



I have to fly out early tomorrow morning for a work trip all week and I had planned a trip with the bike next weekend, which likely isn't going to happen unless I can identify the issue and fix it and test it Thursday evening when I get home.


So, with a limited time window, what are the items to check here?  Could the short from the pipe have damaged other components in the system?  For those who have gone through ignition system troubleshooting, is there a quick order of things to go through and qualify?


Thanks in advance.

Will be able to check the fuel pump tomorrow morning before I take off with a 9V battery.


My main concern is with the wiring harness, having part of it melted against the pipe.  Could this be affecting the required power for the fuel pump on startup?  I know it takes a lot more power on start-up versus normal running, which explains why it was hard to start but ran fine.  How could I qualify that?

Any of the leads that were damaged coaxial or shielded conductors?

The only thing that was physically damaged was the power cable for the fuel pump mid-cable. No other connectors showed any damage.

I have a complete electrical system off a brand new '14 YZ450F that was being parted out on EBay on the way.  CDI/ECU, reg/rect, coil, condenser, wiring harness.  Only thing it's missing is the stator.  So the part swapping will commence as soon as I get back and I will sell off the rest.

Upon disassembly, it looks like the wire that melted was the cable going to the condensor from the Baja Designs wiring harness for the headlight.  Can't quite visualize how a short in that spot would interact with the stock wiring, but whatever.



Tested fuel pump with a 9V, cycles audibly.  Injector passes fuel when the fuel pump is cycled.


No spark.  Plus is corroded badly around the hex, and "sooty" at the tip.


Replaced condensor, CDI, and coil.  No spark.  Next is qualify the stator.  Oh, and try a new spark plug.  



So, ways to qualify stator output?  Voltmeter to the connector?

Testing for spark with a sooted plug?  Could be fooling yourself. 


If the wire that melted was simply carrying more current than its gauge size could support, that's one thing, but if it was shorted, and was tied to the power side rather than after the load, it would have pulled down the voltage of the entire system.

Yep, well aware the sooted plug is likely the problem. I had a fast system for swapping thru components and a bit of time after the auto parts stores had closed.

What causes a 4T plug to foul anyway?

5 things, usually, and a possible 6th. 


  1. Oil fouling
  2. Rich mixture
  3. Weak spark
  4. heat range too cold (see 5)
  5. Failure of the spark plug to reach operating temperature and remain at that temp for at least 5-10 minutes (most common cause)

#1 is obvious, but not common.  2 & 3 form a conductive soot deposit.  #5 is the most common culprit. The 6th is unusual: When the engine operates for most of its time under extremes of high power output, mostly full throttle extended acceleration, and such, a conductive glaze can develop that will produce a misfire under heavy loads due to shorting the spark.

Running MXA map. Can smell gas from the exhaust under normal operation. Plug is dry and sooty (doesn't look like a fouled plug from a 2T). Bike has plenty of comp and power so I don't suspect rings.

So, after a day's ride, it still looks dry, black, and sooty?  Not mid brown and clean?


Probably need to back off the fuel at least in the lower cell ranges.

No idea. 60h on bike and only removed it for the first time last night. IMS tank makes frequent access somewhat prohibitive.

Tried new spark plug, nothing.  Going to find a multi-meter and start qualifying the various parts of the system until something shows up weird.

Maybe something screwy with the kill switch?

I've had kill switches do weird things like that before on 2T's.  How do you even qualify a kill switch?  Just put on a new one, or is there a continuity spec?

Yeah, there are a few things you can do... I'm not 100% sure about the injected 450F, but follow the kill switch lead down to the connector, disconnect it and kick the bike over. If there is spark, you found the problem. Otherwise, will have to dig deeper. I don't have the wiring prints for a 14 yz450, or id give you some more checks.

How do you even qualify a kill switch?

They're easy. Connect a VOM to both leads.  It's supposed to be open when not pressed, closed when pressed.  If it passes that test, hold the meter in your hand while you wiggle, jiggle, and bang on the bars.  Should see nothing but an open circuit unless you push the button.

Killswitch checks out.


I've replaced the stator/pickup, reg/rect, condensor, ECU, coil, spark plug, and wiring harness.  Still no spark.


Any other ideas?  Not having a second set of hands makes it tough to check voltage of the stator when kicking.


Entertaining the idea of just parting it out and getting a new bike at this point.  No local shops know a damn thing about diagnosing EFI bikes, and I'd probably end up with a $500-1k bill for someone else to learn on my stuff.

What voltage should the stator put out when kicking?  The manual is kind of useless for checking anything besides resistance on all of these.

Well, the fuel pump and condensor are getting DC voltage when kicking.  Can't really tell how much because I only have two hands.


The spark plug boot is also getting voltage (where it contacts the spark plug).  But still no spark, and using a few brand new plugs.


Seriously, F this manual for not giving any voltage specs on this.  All ohm readings are in spec, but nothing about required power at startup.

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