I am still working from time to time on my "project" '81 Yamaha. My main problem is starting, simply not getting enough "Ooooomph" to the plugs. She will often start as I take my thumb off the started and the power goes to the spark at the last split second as it is not used for turning the still-spinning motor. I have put in new plugs, checked gaps etc,. I was thinking of replacing the HT leads but an aquantance who knows more about it than be advises against it as the leads are integrally moulded to the coils and he recons it is more likely to be points anyway.
Yesterday I bought the bike back from a short run out and filling her up and due to works going on at the front of my house i was not able to put the bike in the usual place so I left it and busied myself elswhere. two and a half hours later I went to shift the bike and found I had left the ignition "on" and that battery which was fully charged was now as flat as a cow-pat. The only thing using power would have been the neutral light.
It seems to me that the battery should not have drained to zilch in such a short time. If I have a short (ground??) somewhere on the ignition circit what is the best way to locate it??? as this may just be a big clue to my starting problems.
How old is the battery? It could just be on its last legs.
Shorts can be difficult to track down. You basically have to find out where the current is flowing. First thing is to get a multimeter, and see what the current is flowing out of the battery. Then see what the current is through the neutral light circuit. If it's not equal, then you have to find the other sources.
A basic understanding of electricity is a good thing to have:
Ohm's law: Voltage = Current * Resistance
Power Relationship: Power = Current * Voltage
(combinations of the above are handy as well)
Kirchoff's Voltage Law: The sum of the voltages in a closed circuit = 0.
Kirchoff's Current Law: The current flowing in = the current flowing out.
Google is your friend for more thorough explanations.
Yeah, reading your description my suspicion is on the battery as well.
I would go with the battery too, its obviously not holding a charge if the neutral light flattens it and I suspect its right on the limit and just managing to deliver enough current to turn the engine over and start it. The fact it sometimes just catches as you let go of the starter button is due to what known as back EMF (Electro-motive force), its an additional but very brief pulse of voltage/current generated in the coil as the current is removed on the primary side and the induced field in the coil collapses. In effect it increases the intensity of the spark hence aiding starting, but it lasts only for milliseconds. Its not a problem on the HT side but in the old points/condenser systems the purpose of the condenser was to absorb and surpress the Back EMF induced in the LT side which would otherwise cause erratic sparking and lead to contact face errosion and inaccurate dwell angles.....I am sure I am in the ballpark, my EE lectures were a long time ago so I will stand corrected on the finer details
You can always take the battery to a auto shop and have them check it to see if it is holding a proper charge// Most places here in the US do it for free :thumb:
I think that they acctually put the battery under a load to test the voltage under draw and still :thumb:
Cheers guys. The battery is less than a year old and holds up well, I often leave the bike for a week and the battery is fine but i will get it checked out. I will also check current at battery and nuetral light. Ta.