Stupid Express Question


really really really dumb question - 2 part

Do I need a battery in order to obtain a spark?

If so how would one repair the lead entering the battery, mine seems to have fallen out. (the + connection right at the bettery wall)

again, this is my first intro into mechanics...


Re: Stupid Express Question

See Ya Moped Army /

No. The battery is just for the lights.

Re: Stupid Express Question

a bike will start without the battery but the battery cables, positive and negative can't be left hanging without a connection..

on my honda C70 runs without a battery but there's no lights.. no starter motor... etc.

With a battery, the positive battery cable connection pathway is into the positive pole of the battery.... through the battery's plates... out through the negative pole, and finally grounded to the frame.

So, without a battery, the positive cable path is simply to be directly connected to the frame (a ground) to complete the circuit. Then it starts and runs.

Re: Stupid Express Question

Jonas Quimby /

The Express uses two separate electrical circuits, one for the lights and one for the engine. Therefor a lack of battery will have little or no effect on the ignition system.


Running the Express without a battery is a sure way to blow out your lightbulbs. Ever looked into the price of a new headlight?

Re: Stupid Express Question

Thats interesting. if it's got a battery, i'da guessed the lights run only off the battery. And then the magneto's "lighting" circuitry would have a voltage regulator and do nothing aside from recharging that battery.

Why have a battery and not take advantage of it's flat DC voltage supply for lighting? What is the battery power used for.. maybe for a starter motor but not for the lights?

Re: Stupid Express Question

Jonas Quimby /

The battery is used as the voltage regulator. Without it the lights run directly off the magnito and burn out due to the current coming off them.

The horn also draws too much power to work straight off the magnito.

Re: Stupid Express Question

if there's a battery being charged by a variable speed magneto/generator/alternator, that battery needs protection from over-voltage. So, there's also a normal voltage regulator somewhere..

Then, if the lights need the battery as a regulator, it would mean the lights also feed directly off of variable voltage from the lighting coil and need protection from it.. hmm..

this Express electrical system seems very complex.. i admit that the reason for it is beyond me.

Re: Stupid Express Question

Jonas Quimby /

There's a rectifier in there somewhere...

Yes, the electrical system is needlessly complicated.

I plan to tear it out and redo it as simply as possible when I bolt on my Urban Express engine (it uses a 12v system, so I need to redo things anyway.)

Re: Stupid Express Question

A rectifier changes AC to DC .. Full wave conversion of the magneto's AC to DC makes more of the AC wave useful..

Far as i know, a rectifier (one or more diodes) doesn't regulate voltage at all... other than you lose .6 volts acoss each diode (due to silicon's threshold point.. which requires about .6V to get across it)

Re: Stupid Express Question

Jonas Quimby /

I'm well aware of that. But I thought I'd mention it.

There's a wire diagram around here somewhere if you'd really like to check it out in depth.

The part that confuses me is the quasi-conection between the two semi-separate halves of the magnito.

The headlight only works when the engine runs. It works with the battery connected or with the wires disconnected (but dimmer.)

The horn only works when the battery is connected, but it gets a little power if it isnt.

The back brake light and the horn both come on with the key if the battery is connected.

if the engine is at a very low idle, the headlight is on full, the tail light is on full, the turn signals are on and you hit the horn, the engine will idle lower or even die.

All this and more that I cant even remember, as I havent seen my bike in 2 years.

Re: Stupid Express Question

if i had to make one guess that connected most of those symptoms together, i'd say the battery is weak.. internally weak due to age or or partially discharged or not able to hold a full charge for some reason... maybe just corroded connections or a weak ground between battery negative and the engine block..

If so, when the accessories demand power, the battery alone cannot supply all that is demanded.. At that time, current is drawn from the magneto. A large, steady load on the magneto absorbs a greater amount of engine power.. If at idle, the engine could die. The draining effect would exist at high RPM too but might be less obvious.

As far as why accessories get any current at all without the battery, i dunno.. My guess is as you say .. there's some quasi-connection between ignition and accessory power.. perhaps through a large resistance of some sort. Determining exactly what it is would require studying that wiring diagram you mentioned..

Re: Stupid Express Question

Jonas Quimby /

Battery is brand new and fully charged.

That's just how the Express's electrical system is.

Re: Stupid Express Question

i took a look at a '81 wiring diagram.. Headlight and horn are run directly off one of the two lighting coils.. they are not connected to the battery in any way. Nor is their power rectified so it's AC and voltage varies with RPM..

The battery is just an appendage, added as if as an after thought.. simply spliced into the harness between the SCR and ground. So, everything should work without the battery. Since battery power only supplements the other accessories, engine RPM would be related to power delivery to those other accessories.

This bike's system is not over complicated.. it's over simplified .. unsophisticated. My guess is the addition of a battery allowed them to save money somehow .. perhaps by using smaller or weaker designed components in the magneto..

Re: Stupid Express Question

No,you missed something there Joe. I have a manual.......I'll check..........but there is definitely AC converted to DC to charge the battery. Take another look. don-ohio (:^D

Re: Stupid Express Question

i didnt mean to say that.. i do see the SCR in line with the battery .. the battery is connected to one of the two lighting coils..

But the headlights / horn power is not rectified.. they come off the other lighting coil.

Re: Stupid Express Question

Wow guy's I know more about the express's electircal system then I had ever wanted to know! Kidding...

I dont actually want to ride without battery, it's just that I can't get it to start. I know that it worked last fall, asw I purchased it off a friend.

As far as repairing the lead off the battery, I'm just going to strip the wire down a little and try to jam it in, I'll let you know what happens...

Am I to asssume that once I have the battery installed properlyy, i should be able to turn the lights and horn on regardless of being able to start the moped?

Thanks again!

Beginner, but fast learner...

Re: Stupid Express Question

There are no stupid questions... only stupid answers lol

Re: Stupid Express Question

Jonas Quimby /

As mentioned somewhere up there. With a good battery the horn and some of the lights will work.

With a good battery and the engine running, the headlight will work too.

And for whatever reason, with no battery and the engine running your headlight will be dim and your horn wont work.

Re: Stupid Express Question

Will Percival /

Hello, been awhile since I've been here but looking at this post, it appears that you have missed something...

The Express WILL run without the attery... BUT where the battery connects (4 wire connector) there is a manual connection you must make to complete the coil signal. 2 of the 4 wires are black with a white tracer. These two must be jumped together to make the coil fire.

Battery connector


Black/White------------------|[] []|----------------------Red

Black/White------------------|[] []|----------------------Green


Merely jump the gap with a wire on the two black wires to get spark.

You WILL burn out your headlight without a battery to take the overload.

Re: Stupid Express Question

The talk about burning out bulbs because of not having a battery is interesting. I found a product called bat-pac at that replaces the battery and gives better performance to accessories at idle than a battery could. I'm not a salesman!!!

NEED HELP! All I have on my engine is a magneto (flywheel). There is no generator. Can I take power from the magneto, convert it to dc to run my lights OR do I need a generator. There is only one wire coming from the coil. It is a GXH-50 honda engine.

Re: Stupid Express Question

Jonas Quimby /

Ahh gimmics.

Any time you see a "magic box" for sale, it's time to do some extremly heavy research before buying it.

When they give you a box and say it works such percent better, then just repeat the sales drivel every time you ask what it actually is, that's a bad sign.

All that bat-pac is is a large capacitor in a box, I think. I cant see it being anything else.

This doesnt neccisarily mean it wont work... But at $55 for a $10 capacitor, or $12 for the actual honda battery, I know what I'd do.

Want to post in this forum? We'd love to have you join the discussion, but first:

Login or Create Account