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Post by shinysteve on Nov 15, 2014 11:18:21 GMT -5
hi I have a 1979 xs650e fitted with aboyer bransden micro digital ignition system. The bike starts ok but when revved will just cut out over 3000 rpm. Unplug the main connector from the alternator and it will rev perfectly. thought it might be coils , replaced these, thought it might be regulator/rectifier, replaced them with a solid state version. resistance on the stator of the ignition system checks out ok, any ideas.
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Post by grizld1 on Nov 15, 2014 17:56:08 GMT -5
Check resistance of the alternator rotor. If the rotor has a partial short you'll lose current with the alternator plugged in; a dead short will cause the main fuse to blow. For specs and procedures, download the service manual at www.biker.net. |
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Post by Burns on Nov 15, 2014 20:02:53 GMT -5
hi I have a 1979 xs650e fitted with aboyer bransden micro digital ignition system. The bike starts ok but when revved will just cut out over 3000 rpm. Unplug the main connector from the alternator and it will rev perfectly. thought it might be coils , replaced these, thought it might be regulator/rectifier, replaced them with a solid state version. resistance on the stator of the ignition system checks out ok, any ideas. When you say "just cut out" do you mean the engine dies or thst it won't rev over 3000? Have you put a strobe on it to see if the ignition is advancing? |
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Post by grizld1 on Nov 15, 2014 22:24:33 GMT -5
Yo Burns, Steve already did the test that signifies. The defective alternator is sapping current. With the alternator connected, the ignition isn't getting enough power, with the alternator unplugged the ignition works fine. The flaw isn't in the ignition, it's in the charging system. BTW, with a Boyer ignition the advance won't work as it should if the box isn't getting sufficient current.
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Post by shinysteve on Nov 16, 2014 6:44:20 GMT -5
just done resistance checks on alternator. across the three white wires reads 1ohm, white wires to housing is infinity, across the slip rings on rotor is 5ohm. the bike was charging up to 14 volts, but I will put it back together next weekend and see what happens to the voltage when the bike cuts out. thanks for your ideas
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Post by jetmechmarty on Nov 16, 2014 10:22:45 GMT -5
To add to what grizld1 posted. The rotor is a very common failure item. It is due to the wiring insulation technology used at the time these were built. Age, heat, and vibration kill them. If you find it faulted, it can be rewound. A proper rewind should last from now on. I've been running a rewound rotor since 2002.
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Post by grizld1 on Nov 16, 2014 10:55:48 GMT -5
It surprises me that your rotor checks out OK at 5 ohms, Steve. The culprit is going to be somewhere in the charging system, but it looks like the rotor has been cleared as a suspect. But as Marty says, old rotors are trouble. They often fail suddenly, too. A few years ago I took a D-model that I was refurbishing to a Yamaha 650 Society rally. I checked the charging system before loading up the bike--rotor showed 5 ohms. Less than 30 miles into the rally that same rotor developed a dead short. After you've run down the gremlin in the charging system you might want to get a fresh rewind; it's not a question of whether your rotor will fail, but when.
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Post by Burns on Nov 19, 2014 14:38:35 GMT -5
I'd heard that the BB's won't advance with low current, and it was pretty clear that the charging system was a drain - if it was a dead short I would think volts would go to zero and the motor would die so I wanted a clear up on that.
But I was wondering if he had tapped an ignition wire into the charging system loom.
I'd like to know what his voltage at the battery and at the coils is when he experiences what seems to be a "no advance" condition.
I wasn't second-guessing your diagnosis, just curious as to all of the symptoms.
BTW, I'm lovin' my FJ's (got 2) but would love to add a cosmetically stock '79 XS (you know - just the basic "make it better" mods)to the stable.
I lurk here from time to time and am glad you fellas are still making the world safe for my favorite old twin.
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Post by grizld1 on Nov 19, 2014 21:18:33 GMT -5
There are very few wires to hook up in the Boyer system, Burns--two wires from the timing plate to the box, and at the box a ground wire, a power-in wire, and the wire to the coil that breaks the ground contact and makes the current seek ground through the secondary windings and plugs. I can't think of any way to get those wires crossed up with the charging system that would still let the bike rev out with the alternator unplugged. Can't be a dead short; when that occurs the main fuse blows.
May you find a fine green and gold 79 Standard with a seller who doesn't know what he has!
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Post by Burns on Nov 20, 2014 18:00:27 GMT -5
ah yes, "may the odds be ever in my favor." I'm seeing fairly ratty XS's going for over $3K and ones I would not be proud of at 5! And those are usually Specials (go figure).
The FJ1200's are being given away! I bought one for $600 that needed $150 to make it a runner with fresh rubber,chain and battery. How can you beat that?
I'd still like to know the voltage at the coils and at the battery (inquiring minds want to know).
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Post by grizld1 on Nov 21, 2014 9:26:02 GMT -5
Yep, there are too many twits snatching up the old twins and playing Me Too with their Sawzalls, stamping the same things out of the same cookie cutters and yapping about their "creativity." I yearn for the days when the XS650 was the most despised motorcycle on the road and I could pick up nonrunners with title for a couple of hundred bucks, and decent running machines for a little more.
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Post by Burns on Nov 21, 2014 18:04:04 GMT -5
Well at least the clean "standards" will be too expensive to cut up and they'll survive the "bobber" fad.
Maybe I'll stumble on to one at an estate sale of something.
Coming off the FJ it will feel like a 250!
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Post by grizld1 on Nov 21, 2014 21:48:34 GMT -5
The FJ is a fine bike for sure, very agile for a machine of its size. One of the best rides of my life was at the Yamaha 650 Society Smoky Mountain Rendezvous in 2005; I was on my SV650 Suzuki, following Greg Johnson, who showed me what a well ridden FJ1300 could do. It was coil load cornering in every turn--bounce in off the brake and bounce out on the throttle.
AW, JEEZ! I'm sorry, Steve, I just realized that we highjacked your thread! We're gonna to stop the nattering right now, and I'm blaming Burns for leading me astray.
How are the diagnostics going? If the voltmeter isn't informative, you might try powering the ignition straight off the battery as a test.
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Post by shinysteve on Nov 23, 2014 10:21:57 GMT -5
right, I thought I was getting somewhere when I bypassed the ignition switch, the bike revved properly. then realised I was bypassing the charging system also. when the bike is running if I unplug the regulator wire there is a spark and the engine picks up and revs higher as if there is a drain somewhere. the voltage at he battery goes up to 13.9 when charging so I can't see a problem there.
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Post by grizld1 on Nov 23, 2014 11:28:49 GMT -5
Steve, try running a test wire with a 10A fuse straight from the battery to the ignition and leaving everything else hooked up for the moment. Your ignition should be powered from the R/W power-out wire from the kill switch. Test by connecting the bypass wire to the brown power-in wire to the kill switch, and if the grief persists, hook up to the R/W wire and see what happens.
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