Now Heres a Stumper!! Anyone ever come across this??!!

[XSLeo]

The original stock headlight was a 40/50 watt sealed beam.
Converting to an H4 bulb is a good thing. It does draw a bit more current, just make sure all the connections in the headlight circuit are clean and tight. Don't forget to clean the switches too.
Leo

 

[locoleon]

Thanks gents for all the suggestions..
Here is an update:

1. Bike running - Headlight off
- 13.2 volts at idle
- 14.4 volts at 3k rpm

2. Bike running - headlight on (bike idles fine till you twist the throttle - bogs until you reach a higher rpm)
- 12.3 volts at idle
- 14.4 volts at 3K rpm

3. I by-passed the harness and wired up the headlight direct to the battery with wires (so the headlight is on)
- 12.3 volts at idle
- 14.4 volts at 3k rpm

4. I tested the stator - resistance at the 3 white wires. unplugged from the bike. Bike off
- resistance on the volt meter when I touched the red & black wire together is 1ohm
- resistance between each of the pairs of white wires was consistentd at .5ohms (1.5ohms-1ohm = .5ohm)

5. I tested the three possible connections between the white wires by probing from the backside of the connector. I used the voltmeter set on the AC scale to test
- connector plugged into the harness again with engine on.
- Im getting about 12 AC volts on each of the three combinations of white to white that I'd probe.

The alternator seems to check out ok, new rotor, new reg/rec, new bruches, new battery YET it seems to choke and bog down when the headlight is on and you go to accelerate.

Also, I installed an H4 45/45w bulb for all these tests. It had a stock H4 60/55W bulb.
The new bulb doesnt make a difference!

Any thoughts?

Thanks!!

 

[locoleon]

Any of the connections grounding?
What happens if you turn the switch on with the headlamp unplugged?

oop.. missed this one..

The answer is nothing. Makes no differnce in the voltage reading at idle or at throttle.

 

[peanut]

mmm well those readings are fine which would seem to suggest you need to look elsewhere unless there is possible a intermittant fault in the light switch or the loom. I take it you mean DC volts not AC volts

I take it that the charging output didn't drop when the engine faltered at high revs ?

 

[weekendrider]

oop.. missed this one..

The answer is nothing. Makes no differnce in the voltage reading at idle or at throttle.

Then it would appear to me the light doesn't have anything to do with it, big, small or otherwise.
The loss has to be in the wiring or another component.

 

[Dennis]

do you have TCI ignition?

 

[trance]

Then it would appear to me the light doesn't have anything to do with it, big, small or otherwise.
The loss has to be in the wiring or another component.

I agree with this. I would think that the problem is:

1) you are not getting (for whatever reason) enough power to the spark.

2) the headlight draws enough power that there is not enough power to the spark, when the headlight is disconnected, there is enough (total) power.

Start the troubleshooting process for your entire electrical system. Start by load testing the battery - it does seem that your charging system is working correctly, so possibly your battery is just not good.

If it does test good, start checking to see if the rest of the components are OK. Perhaps you have enough volts, but not enough amps of charging power. Perhaps you have a faulty component or shorts in the wiring. maybe a bad coil or something in the ignition system.

 

[retiredgentleman]

mmm well those readings are fine which would seem to suggest you need to look elsewhere unless there is possible a intermittant fault in the light switch or the loom. I take it you mean DC volts not AC volts

I take it that the charging output didn't drop when the engine faltered at high revs ?

Measuring AC volts coming from the alternator 3 white wires is correct................its a 3 phase alternator, which means it produces AC voltage/current. His charging voltages appear to be quite normal.

He should look at area of the headlight switch for a partial short circuit.

 

[peanut]

Measuring AC volts coming from the alternator 3 white wires is correct................its a 3 phase alternator, which means it produces AC voltage/current. His charging voltages appear to be quite normal.

He should look at area of the headlight switch for a partial short circuit.

ah I see thanks for that .

From the results the op has given, the problem doesn't appear to be anything to do with the charging system or the battery yet the symptoms are classic battery overload from poor charging or short circuit etc.

The light switch could be faulty giving an intermittant fault but surely that would show up on the multimeter during testing if that was the case.

 

[GreasyC]

Those may be normal voltages for the charging system but at low rpm the voltage is still lower with the headlight on than the headlight off so anything in the ignition circuit that's become weak is going to struggle here first. Check the spark quality and use a timing light to watch what happens as you pass through this trouble range. It has to be weak or intermittent here, there's just no other possibility. Mixture, compression, spark right? And there's no way the carbs or the piston rings could change what they're doing when a switch somewhere is used. The only possibility is poor spark, but that leaves a lot of parts to check still. Keep digging.

 

[locoleon]

Thanks gents.. I'll keep looking.
This time my focus will be on ignition..
I'll check the plugs and slap in new ones to begin...

 

[Goldy]

My old '75 ran an halogen H4 no problem at all. I recommend you follow the before mentioned suggestions and check for voltage drop across the main switch as well. Most of these bikes suffer form some degree to voltage drop. I cured my troubles by installing a small relay between the coil wiring and battery to give the coils full battery voltage and have had similar success by replacing the standard wiring between the battery and main switch with much heavier 12ga wire. Made the bike a whole lot easier to start and improved the whole running range.