Question about Honda VF 750 C Magna Motorcycles
It sounds like your battery is not getting charged, so you're running your bike with a "total loss" electrical system. Your bike will run--for quite a while if the headlight isn't on--off the stored energy in a battery.
If this were a car, the immediate place to check would be the alternator and / or the alternator belt. With a motorcycle, especially one of this vintage, I would actually start somewhere else. One of the most common reasons that a bike will fail to charge is that it has developed ground issues. Double-check the negative cable attached to your battery. The other end most likely attaches to the engine or the frame with a big bolt. Look for any rust at that mounting point. You probably won't find any, or else the bike would never run very well, but it's an easy first check.
Charging problems I've had with older Honda motorcycles have often been with the voltage regulator or with one or more connectors in the electrical system, rather than with the stator itself. Trace the output wires from the stator to the voltage regulator, which is usually mounted away from the engine (it's often near the battery box or under a side panel). With the bike running, use a volt meter to check two things: (1) output from the voltage regulator; and (2) raw, unregulated output from the stator into the voltage regulator. A bad regulator may be putting out voltage that's too low, in which case the battery's stored energy is tapped to make up the difference. On the other hand, if you're not seeing ANY voltage coming out of the regulator, make sure that juice is being fed into the regulator so it has something to do.
If you're not seeing voltage on the input side of the regulator, the problem has been narrowed to the stator or to a bad connector in between the stator and the voltage regulator. I have seen a number of problems arising from low-quality wiring insulation used in 1980s bikes; it's much cheaper to fix that than to replace the stator in your bike. Alternatively, if you're seeing input voltage but not output voltage from your regulator, I'd suspect you may have found the problem. I believe, though I'm not certain, that Honda still used a mechanical as opposed to digital regulator on this bike, and those mechanical regulators do go bad. You can find used but warranted replacements for not too much money online; depending on how universal the regulator is (Honda used the same voltage regulator in all of its motorcycles from ~1971 through 1978), a brand new one may not be all that expensive, either.
A final, somewhat random thought is that you should also take your battery to an auto parts store to have it checked. A heavily sulfated battery will test out at 12.6 volts, but it won't be able to store its rated amperage. A battery like that may work well enough right after it's been taken off an external charger, but it won't have the amps to turn over the starter after it's been sitting for a while. This doesn't sound like what you're experiencing, which is why I didn't lead off my solution with this suggestion, but a weak battery will put a lot of stress on your charging system and can can lead to some odd symptoms.
Posted on May 27, 2011
Needs new battery or not charging
Posted on May 27, 2011
a 6ya expert can help you resolve that issue over the phone in a minute or two.
Best thing about this new service is that you are never placed on hold and get to talk to real repairmen in the US.
the service is completely free and covers almost anything you can think of.(from cars to computers, handyman, and even drones)
click here to download the app (for users in the US for now) and get all the help you need.
Posted on Jan 02, 2017
Tips for a great answer:
Oct 13, 2015 | 1986 Honda VT 1100 C
Apr 02, 2010 | Honda CMX 250 Rebel Motorcycles
Dec 05, 2009 | 1986 Nissan 300ZX
Nov 13, 2009 | 1985 Honda GL 1200 Interstate Gold Wing
Oct 25, 2009 | 1986 Honda VT 1100 C
Sep 05, 2009 | 1986 Yamaha RD 350
Jun 30, 2009 | 1986 Honda Accord
Apr 26, 2009 | 1986 Honda Prelude
Apr 10, 2009 | 1986 Honda VT 1100 C
628 people viewed this question
Usually answered in minutes!