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Discussion Starter · #1 ·
A bit of background. Back in the day, I am going to date myself, I raced 250's-- Yellow Tanker, TD1, TD1a, TD2w --in AAMRR and CMA events. I was my own wrench but got parts support from Yamaha NA. Flash forward. A few years ago a good friend gave me an RD350 that he bought to commute with during the 1974 gas crisis./ Scared the P out of him and he stored in his warehouse. It had 1,060 miles on it when I got it. I did all the usual things to get it running--carbs, plugs, timing, cleaned out tank, replaced fuel lines, rebuilt front caliper and master cylinder. Bike started, ran well. Went for a back road. blast. Hitting the redline all the way through the gears. Then it turned off just like the ignition had been turned off. No splutter, ragged misfires. Nothing.
It wouldn't restart. Finally called the wife who got the truck and came and got me. This has been the pattern ever since. I am very frustrated because I moved to NC and was planning to ride the Tail of the Dragon.
I have replaced coils, condensers, points, plug wires more than once. I checked and cleaned all the wiring connections. Checked the battery charge after a turn off and it was good. Writing this I realize I have not checked the ignition switch. Is there anything in the switch that could be defective? I have been debating buying a Dyno ignition but worry that the problem is elsewhere and I would be wasting my money
If any of you have suggestions, I would be very very appreciative.
Dragonman
 

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Wiring diagram was an easy find and your bikes electrics are dead simple, so you can easy bypass any switches to test them using the wiring diagram, all you need for that is to rig up some jumper wires. Most of the items on your list can be meter tested to confirm they are good or not and the expected meter readings are right on the wiring diagram.

I take it the failure is on both spark plugs, so that suggests something like a switch.
 

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Discussion Starter · #4 ·
No scope but yes I do have a multmeter and the factory service manual. Time to bypass the ignition switch and check resistances? I wonder if the kill switch could cause a turn off? I assume both plugs because it is a clean shutoff. No misfiring, backfiring. Happens on acceleration only.
Thanks for getting back.
 

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Scope is the best way to test the alternating current output from the alternator, but for basic trouble-shooting the multi-meter will find most problems, make sure the ohm reading sensitivity is set high enough to detect a small amount of resistance in the circuits being tested, to know your meter is sensitive to very low resistance, you can test the resistance of the skin on your thumb (y) if the meter reads that it will read anything.

Look for signs of heat damage on components, like the condensers.

... wish some people would hurry up and get here to ride today
 

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Check ignition switch and ALL the connectors.
I once had a guy who was well into electronics tell me what I found on a Yamaha wasn't possible, until I explained exactly what I thought was happening.
An electrical connector had gotten damp and corroded.
It was acting like a capacitor and charging up well above battery voltage.
 

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Check ignition switch and ALL the connectors.
I once had a guy who was well into electronics tell me what I found on a Yamaha wasn't possible, until I explained exactly what I thought was happening.
An electrical connector had gotten damp and corroded.
It was acting like a capacitor and charging up well above battery voltage.
I can see "acting like a capacitor" being a confusing analogy to a sparky.

Damp corroded electrical connections should act like a resistor.
... and a capacitor doesn't output any higher voltage then you put into it, that would be a coil or voltage transformer.
 

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I can see "acting like a capacitor" being a confusing analogy to a sparky.

Damp corroded electrical connections should act like a resistor.
... and a capacitor doesn't output any higher voltage then you put into it, that would be a coil or voltage transformer.
That's what made it so confusing.
Bob wasn't just a 'sparky' though, he worked at Aldermason doing some sort of 'classified R&D (the British nuclear establishment)
I met some interesting characters working as a mechanic/service writer/workshop manager/etc.
The alternator is putting out a much higher voltage, being rectified and relying on battery to 'smooth things out' but, there are transient spikes well above rated voltage (you need a peak voltage adapter on meter to see them)
The nominal 12v can easily get above 17v which is what was happening so 'acting like a capacitor' is the correct explanation.(electronic ignition primary side 12v can very easily get over 310v spike! Highest I've measured was a Suzuki VS800 at 318v)
I may have been 'just a mechanic' at the time but I had to learn a lot of stuff to explain things to customers who wanted to know 'WHY'. (often related to costs)
 
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