Motorcycle Repair: weak battery, honda nighthawk 750, 1982 honda nighthawk

Question
i have a 1982 honda nighthawk 750,if i start it up 4 to 5 times within an hour the battery goes dead.I recharge itfully,same thing happens ,can it be the alternator not charging? THanks

Answer
Hi William,

The problem might be a couple of things.

One is a weak or faulty battery cell.
The battery can be load tested for faults when fully
charged by a auto or motorcycle dealer
with battery testers.

If your battery is okay then you can check the
charging system with a volt or multimeter.

One thing that causes people some problems
is that the charging system on these bikes
does not charge below about 1700 RPM.
That means if you do short drives around town
the battery will get little charging.

Connect a multimeter to the battery terminals.
Set it to check voltage up to about 20 DC volts.
Start the bike and with headlight on high beam
rev the engine over 1700 RPM.
Check the volt reading, it should hold at about 14 dc volts.

If the voltage drops below 13 then the bike is not
charging.

You can buy a small "battery tender" which is
a low current charger that you can leave connected
to the battery to maintain it when parked.
http://www.amazon.com/Battery-Tender-800-Waterproof-Charger/dp/B000CITKCE/ref=sr...

If you find the bike unable to keep the
voltage above 13 volts then you may
have to check the alternator stator
output and if that is okay then replace
the regulator.

The stator has 3 yellow wires that should
output over 40 AC volts between any two of
the yellows. It can be unplugged and checked.
None of the yellows should have any connection
to ground or the bike's frame.
When you speed up the engine the voltage should rise.

If the stator output is good, check wiring
and connectors and then replace the regulator.

Good luck!
Wayne S.

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