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1972 Yamaha G7S - Headlamp Power Question


rigsbee
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Good Evening,

I picked up a 1972 G7S a few weeks back and trying to awaken it from its slumber.  Electrically, I have cleaned all the connections and have everything working off a brand new battery except the headlamp.

I read in an older post (Sacha's) that the headlamp circuit is powered by the magneto, and not the battery (similar to a DT). I have a rectifier, and no voltage regulator that I can find.  The headlamp is intact.

If that is the case, I will finish cleaning the gas tank, oil tank (shall I flush it with mineral spirits?) and order a carb kit and get this running.  It has good compression and spark, so will sort the fuel side out.

Thank you!

 

 

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Standard practice, the headlight is ac. There is sometimes a resistor mounted on the frame (somewhere it will get some cooling) that acts as a load sink to keep the power down.

In some cases the load on the system was carefully matched to the charging/lighting load so the was no need for the resistor but leaves you with a system with no spare capacity. No problem in theory until your components age, you can see losing 10% efficiency due to age/ corrosion, will give issues. Normally with the indicators. An arch villan  of the 6v universe.

Later  (late 70's) tec moved on and they were using Zener diodes (cleaver variable resistance that keeps a constant voltage) a forerunner to proper voltage rectification. These are retro fitted to older bikes to stabilise the electrics as they are more efficient. Helping the headlight and battery last due to more consistent power.

You could have any one of the above.

Flushing the oil tank is probably a good move as you don't know whats been before. Some old oils like castrol R don't mix very well with modern oils. Can clog the pipes. Most 2 stroke owners (me included) , even the proper anoraks replace the oil feed pipes with clear ones for peace of mind.

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Would love to see pics of the G7S. ❤️ I’m hoping to get mine back one day. :) 

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Well hello stranger, long time no see.

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7 hours ago, Cynic said:

Well hello stranger, long time no see.

Hiya Cynic! I’m back! 😆 How’s it your side of the pond? Hope all is well for you during all this madness!

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Yep good (for me and mine). On furlough, luckily paid and the kids are old enough not to be a pain in the arse so more of a bad holiday really, not to mention seriously curtailing riding my new to me (last October) gen1 Vmax. Could be a lot lot worse. 

Ok your end?

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Oh ya! Living the dream. LOL Luckily I can work from home so I’ve not lost my income. :)  so close to finishing my dissertation I can taste it. Can’t wait to have that done. 

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On 4/26/2020 at 5:06 PM, Sacha said:

Would love to see pics of the G7S. ❤️ I’m hoping to get mine back one day. :) 

Yea welcome back Sacha,  please stay 

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19 hours ago, jimmy said:

Yea welcome back Sacha,  please stay 

Aw! Thanks man! Did you miss me... and my schoolmarmy ways? :biglaugha:

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