fizzy Posted October 1 Posted October 1 Agree with Tomek, charging system is weak. As stated, check battery electrical connections, also large 3 pin connector between stator and R/R (regulator/rectifier) and starter relay/whole bike fuse as both can melt. If all good, test the stator output. Do test with a fully charged battery as bike will be running on battery power alone. I say stator as dicey stator will give low output (less than 13V) while dicey R/R will give extra high output (15V+), generally speaking. Both of which are bad. A bad battery can also give low readings, so have battery tested if in doubt. 1. Basic test: disconnect large 3 pin from above, run engine and test voltage output from 3 stator wires all 3 ways. Should be about 60VAC @ 5000rpm with all 3 readings being the same. 2. Load test, same as #1 but substitute 60W 120V incandescent bulb for voltmeter. It will burn bright at 5000rpm. Quote
SwampNut Posted October 1 Posted October 1 12 hours ago, bryanhes said: Then started it up and it is at 12.70v at idle. Not at all normal. Yet the symptoms you noted still don't line up with a voltage issue. But who knows on a 25 year old bike. 1 Quote
tomek Posted October 1 Posted October 1 Dude, you have no clue but yet insist on spreading confusion. Counterproductive, really. Quote
bryanhes Posted October 2 Author Posted October 2 On 9/30/2026 at 9:06 PM, tomek said: I'd say 12.35 V at idle is too low. It probably momentarily reads even lower when you get on gas (because injectors draw more current at load vs. light load), and before rpm hit your magic 3000 rpm mark. I don't have XX any longer but my FI Honda VFR 1200f reads around 13.8 at idle. Without engine running 12.35 V is pretty much discharged battery. What does it read without engine running? Ignition on, and ignition off? If I were you I'd hook up voltmeter the way it would allow you to read it while riding. Like get in 3 gear, and start accelerating at around 1500 rpm and see what it shows. I thought it should at least read in the low 13's at idle as most anything else seems to. I'll have to run through more testing of the R/R over the weekend if I get a chance. Currently trying to squeeze in working on this and trying get a high top installed on my van and finish up house projects. Then there is that damn work thing that always gets in the way. 😂 Quote
bryanhes Posted October 2 Author Posted October 2 14 hours ago, fizzy said: Agree with Tomek, charging system is weak. As stated, check battery electrical connections, also large 3 pin connector between stator and R/R (regulator/rectifier) and starter relay/whole bike fuse as both can melt. If all good, test the stator output. Do test with a fully charged battery as bike will be running on battery power alone. I say stator as dicey stator will give low output (less than 13V) while dicey R/R will give extra high output (15V+), generally speaking. Both of which are bad. A bad battery can also give low readings, so have battery tested if in doubt. 1. Basic test: disconnect large 3 pin from above, run engine and test voltage output from 3 stator wires all 3 ways. Should be about 60VAC @ 5000rpm with all 3 readings being the same. 2. Load test, same as #1 but substitute 60W 120V incandescent bulb for voltmeter. It will burn bright at 5000rpm. I'll try to get some more time testing the R/R and doing a load test on the battery this weekend between other projects. I have read that the R/R is a common problem. Are these running issues typical with the failure? Is it possible at ow RPM its not sending enough voltage to the injectors at low RPM causing the sputter/ miss? Quote
fizzy Posted October 2 Posted October 2 8 hours ago, bryanhes said: I'll try to get some more time testing the R/R and doing a load test on the battery this weekend between other projects. I have read that the R/R is a common problem. Are these running issues typical with the failure? Is it possible at ow RPM its not sending enough voltage to the injectors at low RPM causing the sputter/ miss? Yes, possible. It is also possible that low voltage causing intermittent spark on the spark plugs. Do easy stuff first. Have battery tested at auto parts store. Test output from stator. You are correct that R/R is a common failure. Best option is an upgrade to a genuine mosfet unit. Not only BB's but many other bikes of similar vintage. Check out this site for more info and the genuine article for sale. Roadstercycle.com | SH847 & FH027EA Regulator Kits | Jack Fleming If it's in the budget, the FH027AA super kit best bet. FYI the SH847 is an upgrade above the 027 but a little pricey. I have used the FH020AA (previous model) on 2 machines, many years and miles, no issues at all. 1 Quote
tomek Posted October 2 Posted October 2 11 hours ago, bryanhes said: Is it possible at ow RPM its not sending enough voltage to the injectors at low RPM causing the sputter/ miss? More load, more current injectors draw. Although I think ignition is first to suffer from low voltage. So, what you are feeling is most likely ignition cutting off. Quote
tomek Posted October 2 Posted October 2 RR from 2004 Yamaha R1 fits in. Kinda. Gotta trim cooling fins with grinder. That's what I had on my XX. Voltage was rock solid IIRC around 14.0 Volts pretty much at all rpm, load or not. They can be found dirt cheap on eBay. 1 Quote
SwampNut Posted October 2 Posted October 2 12 hours ago, bryanhes said: Are these running issues typical with the failure? Is it possible at ow RPM its not sending enough voltage to the injectors at low RPM causing the sputter/ miss? No not common, yes totally possible. I did a LONG ride with a fucked stator AND reg/rectifier, head/tail light unplugged, and really low voltage. It ran OK. This doesn't mean every bike will behave that way of course. Quote
bryanhes Posted October 2 Author Posted October 2 6 hours ago, fizzy said: Yes, possible. It is also possible that low voltage causing intermittent spark on the spark plugs. Do easy stuff first. Have battery tested at auto parts store. Test output from stator. You are correct that R/R is a common failure. Best option is an upgrade to a genuine mosfet unit. Not only BB's but many other bikes of similar vintage. Check out this site for more info and the genuine article for sale. Roadstercycle.com | SH847 & FH027EA Regulator Kits | Jack Fleming If it's in the budget, the FH027AA super kit best bet. FYI the SH847 is an upgrade above the 027 but a little pricey. I have used the FH020AA (previous model) on 2 machines, many years and miles, no issues at all. I'll pull the battery today and go get it checked. My battery load tester crapped out on me a while back and haven't replaced it yet. I would rather buy better quality and a complete kit if they are superior over saving a few dollars if the value is there. Thanks for the link! Quote
bryanhes Posted October 2 Author Posted October 2 2 hours ago, SwampNut said: No not common, yes totally possible. I did a LONG ride with a fucked stator AND reg/rectifier, head/tail light unplugged, and really low voltage. It ran OK. This doesn't mean every bike will behave that way of course. I prefer to avoid trashing any other components. It runs great and no miss or sputter if I keep the RPM;s above about 3200. Quote
bryanhes Posted October 2 Author Posted October 2 3 hours ago, tomek said: More load, more current injectors draw. Although I think ignition is first to suffer from low voltage. So, what you are feeling is most likely ignition cutting off. If it is load related then possibly why at over 3200 RPM it runs smooth with tons of power. Quote
SwampNut Posted October 2 Posted October 2 37 minutes ago, bryanhes said: If it is load related then possibly why at over 3200 RPM it runs smooth with tons of power. If the voltage goes up at high RPM, then they can be related. I believe you said it doesn't, at least, not by a huge amount. So not likely related, not impossible either. You're chasing a ghost now. You need to fix this, so just fix it and see. Also if you need a battery, I've put lithiums in my last two birds, and everything else, and will never buy another AGM. Quote
tomek Posted October 2 Posted October 2 (edited) 1 hour ago, bryanhes said: If it is load related then possibly why at over 3200 RPM it runs smooth with tons of power. Because at that point alternator could make enough juice so it won't matter. Amperage is rpm dependent to some degree. Edited October 2 by tomek Quote
tomek Posted October 2 Posted October 2 (edited) There might be something else on the bike eating current. Also, you could pull fuses from anything not needed to run the engine, unplug headlight, etc. and test if symptoms disappear. Edited October 2 by tomek Quote
bryanhes Posted October 3 Author Posted October 3 7 hours ago, tomek said: There might be something else on the bike eating current. Also, you could pull fuses from anything not needed to run the engine, unplug headlight, etc. and test if symptoms disappear. Had battery load tested today. It showed 13.09v, under load 12.7 and 209cca under load on a 210cca battery so it tests good. Will check R/R over the weekend and start eliminating possibilities. 2 Quote
SwampNut Posted October 3 Posted October 3 Good start, BUT... The battery has that voltage straight out of the bike? The bike that was only producing 12.something? Or after being charged outside the bike? Quote
bryanhes Posted October 4 Author Posted October 4 On 10/3/2026 at 10:59 AM, SwampNut said: Good start, BUT... The battery has that voltage straight out of the bike? The bike that was only producing 12.something? Or after being charged outside the bike? Yes, no charging before being tested, just removed from the bike. Correct, the voltage running at idle was 12.7 then up to 14.14 at about 5000 rpm. Quote
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.