GEN Light coming on at low RPM - Normal?

[kmisterk]

Depending on how long it's been running in any given ride, my r100t idles between 1200 and 800 rpm. Anything below the 950 mark, and the red GEN indicator light comes on. Is this the light indicating too low of a voltage being created by the stator/generator?

Is it normal for it to be on when you're at lower RPM? Or is this a sign that the stator/generator/some other piece of the electrical system is going bad?

[Kurt in S.A.]

Sounds pretty much normal. The light monitors the voltage on either side of it...one side being the battery and the other side being the alternator output. If there ends being a large enough difference between the two voltages, current will flow and the bulb lights. As long as the light goes out once you get past say 1500 or so, you're good to go. You should look to get the idle up more steady in the 1000-1100 range...better for low end oiling as well.

Kurt in S.A.

[melville]

Yes, very normal. Check voltage at the battery posts at 2500 rpm. Should be somewhere north of 13V.

[kmisterk]

Sounds pretty much normal. The light monitors the voltage on either side of it...one side being the battery and the other side being the alternator output. If there ends being a large enough difference between the two voltages, current will flow and the bulb lights. As long as the light goes out once you get past say 1500 or so, you're good to go. You should look to get the idle up more steady in the 1000-1100 range...better for low end oiling as well.

Kurt in S.A.

It's a bit odd, the range of RPMs across its "running" cycle varies. When it's "cold," it dies if I don't give it some amount of throttle, dipping to about 600rpm before dying. after ~10 minutes, but before about 45 minutes of total "running" time, it idles nicely and doesn't threaten to bottom out and die at around 1000-1200. anything after 45 minutes or so (rough estimate, but definitely not shorter rides), it idles seemingly stable at around 800-900 rpm and hints at the possibility of dying.

It's at that final stage of "engine warmth" that I see the GEN light on.

Yes, very normal. Check voltage at the battery posts at 2500 rpm. Should be somewhere north of 13V.

Good to know! I'll put a voltmeter to it the next time I'm at my dad's place.

[barryh]

Low idle revs when cold is normal. If the idle speed falls away once the engine is fully warmed up then one possibility is the idle mixture is too rich possibly because the fuel level in the bowels is too high, which can be a heavy float or leaky float valve. A test for this is to close fuel tap 1/2 a mile from home and if it then idles nicely on the weaker mixture resulting from a lower fuel level in the bowls, it will confirm the excessive richness theory. You could also try turning the mixture screws in a touch to see if that improves the idle when hot. Idle mixture settings should in any case always be done on a fully warmed engine.

The gen light behaviour is normal but when you do the voltage test at 3000rpm, then frankly I wouldn't be at all happy with 13.5 volts, it should be 14.0 volts cold. For a representative result, it's important to do this test with a 100 % fully charged battery and lights etc turned off. Ideally do it shortly after a cold start as there is a negative temperature coefficient built into the voltage regulator to lower the charging voltage a few tenths when the battery is hot.

[Rob Frankham]

Sounds pretty much normal. The light monitors the voltage on either side of it...one side being the battery and the other side being the alternator output. If there ends being a large enough difference between the two voltages, current will flow and the bulb lights. As long as the light goes out once you get past say 1500 or so, you're good to go. You should look to get the idle up more steady in the 1000-1100 range...better for low end oiling as well.

Kurt in S.A.

It's a bit odd, the range of RPMs across its "running" cycle varies. When it's "cold," it dies if I don't give it some amount of throttle, dipping to about 600rpm before dying. after ~10 minutes, but before about 45 minutes of total "running" time, it idles nicely and doesn't threaten to bottom out and die at around 1000-1200. anything after 45 minutes or so (rough estimate, but definitely not shorter rides), it idles seemingly stable at around 800-900 rpm and hints at the possibility of dying.

It's at that final stage of "engine warmth" that I see the GEN light on.

Yes, very normal. Check voltage at the battery posts at 2500 rpm. Should be somewhere north of 13V.

Good to know! I'll put a voltmeter to it the next time I'm at my dad's place.

This all sounds absolutely normal to me... It's worth rememberiong that this is 1960s technology. No electronics (mainly), no temperature compensation circuits, no mixture sensors and adjustments... just your backside and experience with the machine... and better for it to my mind. it will soon become second nature to keep a bit of throttle on if you have to stop in the first few miles of a journey. You may make some slight 'improvement' by fine adjustment but there's nothing here that leads me to think there is anything wrong.

Rob