yamaha tx 750

[lazyrockinG]

help im trying to find out if any one can tell me how to test charging system on 1974 yamaha 750

[Welsh Wizard]

Not sure what model but have a look here under Yamaha

http://forums.sohc4.net/index.php?topic=17788.0

Yamaha Motorcycle Fault Finding Troubleshooting Guide Manual

[Tman]

The most basic test you can do is to rev the engine with the lights on, and looking to see if the lights flare when it's revved up. A DVM across the battery is the next easiest step...does the voltage increase with revs?

[lazyrockinG]

thanks for the help. its nice to get replies that are helpful and not just to tell me its a piece of junk like other forums . the ole bike was chopped in 70s it still sports the paint from then it has coffin tank and 20 over springer. it also has vintage diamond back king queen seat. it gets lot of looks and comments every where we ride. it brings back memories of my first chopper in 73. same basic look. how do i tell if the stator or regulator are the item thats bad

[McSnotty]

Hi,
To continue you will need a digital voltmeter. They are pretty cheap from most electronic stores now days.
Next thing is to work out if the TX is single phase or 3 phase. The TX was quite a innovative machine so I am assuming that it will be 3 phase. However to check this you will need to locate the wires that come from the alternator - 2 wires of any colour will mean single phase, 3 wires of the same colour (usually yellow or may be red) will mean 3 phase. Set the digital meter to AC Volts (~V) and with the engine running connect the test leads across the 2 wires (for single phase) leaving them connected to the regulator. Revving the engine you should see voltage anywhere from 15 to 30v AC (roughly). On the 3 phase system test for voltage between each of the 3 wires, similar voltages should be seen (but not exactly). Anything below 15v AC would indicate a fault with the alternator. Testing the regulator is more involved which requires special test equipment.
If the alternator is 3 phase there is 2 types of regulation of the charging, most common used by early motorcycles (1970s to early 80s) was to regulate to earth. Yamahas, Kawasakis used this. The second system was to slow down the output charge of the alternator by a reverse current through field windings in the alternator. Hondas used this from 1979 so I don't think this would be used by Yamaha this early.
One main thing to check for faulty charging are the earths within the wiring. There should be a good loop earth lead from the regulator to the battery, to the main frame earthing point, to the front forks/headlight.
Hope that this makes sense.
Let us know how you get on.

Regards,

McSneezy............

[fido]

I thought I had a fairly good idea what bikes the Japs were making in the mid '70s but I had never heard of a TX750. I suppose it was not available in UK. I remember Kawasaki doing a 750 twin but that was a year or 2 later.

[Tman]

He's gone. Sad when there's no follow-up or feedback. I s'pose they post the same query all over the 'Net and hope someone helps out, but I'm starting to think it really ain't worth the wear on my keyboard to reply...

[Welsh Wizard]

Same feeling here, makes you ask why bother even checking through the records to see if any help can be given , may even wait till I see 10 plus post from a new member before wasting any time looking.

[Tman]

Yep, good idea.
I remember writing a screed about someone's problem with the 6.5" vs 6.75" Triumph front wheel spindle problems, looking up years and part numbers and the b*stard never even said thanks or whether it was sorted or not.
{Just venting really......if I know the answer I'll still post it....twat that I am.. }

[Welsh Wizard]

I still think maybe it should be a forum rule that so many posts have to be made before they can post any thing except an intro, maybe 5 post before they can post questions