Sorry for the ambiguity here.. I'm not sure what the issue is with my bike. I have a bunch of symptoms and my hypothesis is that it's a cascading failure and I'm just seeing a bunch of effects down the line.

So here goes: I recently bought the bike, the previous owner mentioned that they were concerned with a fuel line and that they had replaced the stator/rectifier recently.

Almost every time I rode the bike the battery would die. It was an old battery so I replaced it today with a lithium battery, checked the voltage before the ride (13.22V), after about an hour of riding (13.01V) and again when I got home (13.16V).

After seeing it dip from .22 to .01, I worried that it wasn't charging correctly and rode at higher RPM - 7k RPM or so as opposed to 3-6k RPM (the bike is LOUD).

So that may have helped it charge but that does seem like it should be charging at lower RPM - the previous owner said 3k RPM should be enough for it to charge. When the bike is off if I check the voltage it's not dropping by itself.

After riding for about an hour, the bike starts behaving oddly. When coming to a stop, the RPM tends to roam a bit, like it's struggling to breathe. Also, starting from that stop tends to be difficult, feels like a slipping clutch and I have to really give 'er to get it going, but once it's going it's fine. This is usually followed by a dying battery if I don't get home quickly. Also when this behaviour starts, if I shut the bike down and let it sit for 15 minutes or so, everything goes back to normal and it seems fine. I don't think it's related to temperature directly, although maybe when the temp goes up and the fans kick on there's more power draw.

One final thing: it doesn't feel like a 1000cc bike. It feels more like a 600, but when I first fire it up there's plenty of power and it seems to dissipate as a ride. I recently went for a longer ride and at some point it sounded like only two cylinders were firing, and I could barely keep up with my buddy's old CBR 600.

So: coils, CDI, stator/rectifier/regulator, fuel/air? I really don't know where to begin.

EDIT 1: okay, I checked all three phases of the stator, all output ~12-15VAC (I don't remember exactly) at idle, and ~50VAC at 5k RPM. The connector is discoloured though (slight browning around the contacts). I plugged it back in, pulled the headlight fuse to reduce load and restarted the bike to find the battery charging at idle (~1900rpm). I got the headlight fuse back in, let the bike warm up to 105C and heard the fan kick on, and even with all of that the battery still was able to hold exactly 13.56VDC. So in other words, I'm back to square 1. Either it was a connector issue and messing around with it cleared it up, or this condition only comes up after riding for like 1-2 hours, which I suspect since it always seems to start strong. What do I need to look at next?

EDIT 2: I've ridden a bunch today. I checked voltage before and after cold start, then at each stop right before getting back on to ride I'm checking the voltage before/after starting. Here's the results. The bike still feels under-powered but I think that's a separate issue - I think the charging issue is resolved and for now I'm going to attribute it to a connection issue that I inadvertently fixed by pulling things apart and putting them back together. These voltage readings seem quite healthy.. closing the question, I'll open a new one later if it continues to be an issue.

13.21 cold, pre-start
13.50 cold idle
13.26 stop 1 cold
13.45 stop 1 idle @ 88˚C
13.4x stop 2 cold
13.5x stop 2 start @ ?

EDIT 3: Thought everything was fine, but my last stop of the day was a coffee shop for two hours or so. Come back out and... bike doesn't start. 9.4v on the batt.

Jump start, go home, pull it apart and test the R/R and stator again. Everything appears fine except the connector where the stator meets the R/R is getting really hot. Some Fireblade owners say is best to solder the wires rather than use the connector. New stator on the way.

  • I'm going to check voltage and continuity with ground coming out of my stator at idle and 5k rpm. If it seems sufficient I'll check voltage coming out of my regulator/rectifier. Will post here later with the results.
    – Harv
    Sep 1, 2015 at 16:18
  • I suggest you continue to monitor the issue (after a few hours, at idle, at high RPM) and update the post with your findings.
    – Zaid
    Sep 2, 2015 at 7:44
  • @Harv Did you ever get this resolved. It would be great to here about what the issue was. I'm guessing rectifier. Dec 18, 2015 at 17:01

2 Answers 2


It sounds like the root cause of your woes is a battery that is not getting properly charged at lower speeds.

Assuming this is a 14 V charging system, the battery voltage should be close to 14 V while the bike is running. If it isn't, the battery will deplete and affect components that rely on it like the fuel injectors and coils, which would go quite some way in explaining why it feels like the engine is "coughing" or struggling to breathe.

Possible culprits:

  • a faulty rectifier

    If this has been replaced recently it may be indicative that the problem lies elsewhere (in other words, an unsuccessful fix)

  • a dirty connection

    A dirty terminal/connection on the charging cable between the alternator and battery can reduce the voltage seen by the battery. Cleaning up the relevant terminals/connections may be all that is required here. This could also be an issue due to oxidation of the clamp on the battery terminal.

  • 1
    i am going with faulty rectifier :-)
    – Shobin P
    Sep 1, 2015 at 8:25
  • @Anarach : It could be for sure, since the bike is 15+ years old. The previous owner may have had the original rectifier go bad and replaced it with something that is non-conformant to the specs for this bike.
    – Zaid
    Sep 1, 2015 at 8:37
  • Exactly, I ruined my recent battery when I heeded advice of a local mechanic by installing non compliant REC which was apparently working on installation.
    – Shobin P
    Sep 1, 2015 at 8:39

Testing Your Stator

There are three yellow wires that come from your stator. They come out of the left side crankshaft cover and route into your sprocket cover and out along the cast bottom portion of your frame on their way to your rectifier. They connect directly to the rectifier. You can disconnect them from the rectifier and test them with a multimeter. Your first test will be static. The engine is not running. Be sure to disconnect from the rectifier and not just try and pierce the wires with the multimeter end. They are larger wires and insulated a bit more, these are some of the very few wires on the motorcycle that carry AC current.

  • Static Test Set multimeter to ohms and test between all the leads in pairs. The reading 0.1 to 1.0 max resistance.

  • No Load Test Dynamic Test Set your multimeter to AC Volts and start the bike. It should be cold. Have a friend hold the RPM's at 5,000. Test between the leads. You should see more than 70V. If it's below that, you may need a new stator. I would replace, but I'll get to that later.

Testing Your Rectifier

Your rectifier has diodes in it. Diodes are one way valves for electricity, think of a reed valve in a two stroke intake. Since this is a three-phase charging system you need diodes to join the AC current into a single output and convert to DC. I could get more detailed but I want to keep it simple.

  • Rectifier Resistance Test Using your multimeter set to ohms connect the multimeter to the ends of each of the diodes and check the resistance in both directions. You should have low resistance in one direction and higher in the opposite direction. Generally, you will want to see 5 - 40 ohms of resistance in the forward bias direction, and infinite resistance in the reverse bias direction.

  • Procedure Attach the black probe (-) of the meter to the ground side of the rectifier (black wires) and the red probe of the meter to each of the three contacts for the stator. Record the numbers. Then swap around the meter leads (red and black are swapped) and take the readings again. You have thus measured the ground side of the rectifier.

If you have lower resistance in both directions (5+ ohms) then you must replace it.. If you have infinite in both directions you will need to replace the rectifier.

I hope this gives you some troubleshooting tools to remediate your issue. Best of luck.

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