New member with TC90 that dies in night mode

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singring
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Joined: Thu Aug 29, 2013 6:02 pm
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Suzuki 2-Strokes: TC90, DS100

New member with TC90 that dies in night mode

Post by singring »

Hi there everyone...I have a 1970 TC90, just like the one I had when I was a kid, and I have restored it to the point of just requiring a paint job on the fuel tank and side panel. Engine runs great, but not in night mode ( ignition key at setting two). At cold idle, when I switch over to night mode so headlamp and tail lamp are on (speedo lamp does not come on, tho bulb has been replaced) the bike continues to idle, but it struggles a bit. I can ride the bike from this point for about a city block, then engine misses and will die very soon. If I switch back to day mode running, bike will run just fine with no missing. I have gone thru all the wiring, as per the service manual, and have found no faults. I cannot figure out why the engine will die in night mode, after the engine has had a good warm up. Any help is appreciated.
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jabcb
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Suzuki 2-Strokes: 69 T350 thru 75 GT750
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Re: New member with TC90 that dies in night mode

Post by jabcb »

Wiring diagram is here: http://smokeriders.com/diagrams/Suzuki/ ... S_TC90.gif

Your bike has a magneto that is wired separately from the rest of the electrical system.

The ignition switch is one of the grounds.
When in the off & parking positions, the ignition switch grounds the magneto.
When in on & on+lights positions, the ignition switch does not connect the magneto to anything.

There may be a problem with the ignition switch.
Remove the switch, and use a multimeter to check the ignition switch. Compare your results to the chart in wiring diagram.
Do you get an open circuit between the magneto B/W wire & everything else (other wires & the switch housing)?
Are the switch positions tight or is it affected by the kind of movements it sees when riding the bike?
BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 & 75
GT380 72
T500 69 project & 73 project
T350 69 & 71
Honda 85 CB650SC & 86 CB700SC
09 Triumph Bonneville SE
singring
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Posts: 10
Joined: Thu Aug 29, 2013 6:02 pm
Country: Canada
Suzuki 2-Strokes: TC90, DS100

Re: New member with TC90 that dies in night mode

Post by singring »

Thanks jabcb , for the response. When I get some free time I will do as you suggest and test the ignition switch next. The switch appears to be in good condition, it is not mechanically loose. This fault also shows itself when the bike has been idling for 5-10 minutes, the engine labours when you switch to night mode. When I have the ignition switch off the frame I use some jumper cables to make the necessary connections for night mode, and see if the fault disappears.
I will post my results
Thanks again
singring
On the street
Posts: 10
Joined: Thu Aug 29, 2013 6:02 pm
Country: Canada
Suzuki 2-Strokes: TC90, DS100

Re: New member with TC90 that dies in night mode

Post by singring »

I have tested the ignition switch as suggested, and there is no detectable internal wiring fault, and all cylinder movement is like when new. I did take some multimeter readings using the wiring diagram, and hope this may assist:

amperage readings from magneto stator with engine running, stator connected:
NIGHT MODE , with engine at idle
wire colors
G/W to Y/W 4.7
G/W to B/Y 5.0
Y/W to B/Y 5.0

NIGHT MODE, with engine at aprx 3000 rpm
wire colors
G/W to Y/W 5.0
G/W to B/Y 14.0
Y/W to B/Y 11.0

DAY MODE, with engine at idle
wire colors
G/W to Y/W 10.9
G/W to B/Y 5.0
Y/W to B/Y 12.0

DAY MODE, with engine at aprx 3000 rpm
wire colors
G/W to Y/W 30.0
G/W to B/Y 15.0
Y/W to B/Y 30.0


ohm readings from magneto stator, engine not running, stator unconnected:

wire colors
G/W to ground 0.1 ohms
Y/W to ground 0.1 ohms
B/Y to ground fluctuating 2.0 - 5.0 ohms

I have tested the rectifier and it is OK. Next step, check for stator wiring faults at crankcase and stator plate. If none seen, then test lighting coils behind magneto flywheel. Any idea what those coil reading should be for normal operation?
Thanks
singring
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Posts: 10
Joined: Thu Aug 29, 2013 6:02 pm
Country: Canada
Suzuki 2-Strokes: TC90, DS100

Re: New member with TC90 that dies in night mode

Post by singring »

One other question to ponder: if the headlamp lighting coil IS faulty, then for the headlamp to operate in night mode, would there be a tap, or draw, from the primary coil thereby sapping the amperage to the ignition coil, resulting in poor spark at the sparkplug??
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jabcb
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Re: New member with TC90 that dies in night mode

Post by jabcb »

singring wrote:amperage readings from magneto stator with engine running, stator connected
Am assuming you meant AC voltage.

When in on & on+lights, did the resistance check on the switch show an open circuit between the B/Y wire and
1) all other wires
2) the outer metal portion of the switch?

With the switch connected, the coil disconnected & the magneto disconnected,
check these resistances at the wire harness connector for the magneto:
1) between B/Y & ground
2) between B/Y & G/W
3) between B/Y & Y/W
Check this for switch in on & on+lights position.
(Check connector that's part of wiring harness, not the connector that's wired to the magneto.)
BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 & 75
GT380 72
T500 69 project & 73 project
T350 69 & 71
Honda 85 CB650SC & 86 CB700SC
09 Triumph Bonneville SE
singring
On the street
Posts: 10
Joined: Thu Aug 29, 2013 6:02 pm
Country: Canada
Suzuki 2-Strokes: TC90, DS100

Re: New member with TC90 that dies in night mode

Post by singring »

Will do...and will post results
thanks
singring
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Posts: 10
Joined: Thu Aug 29, 2013 6:02 pm
Country: Canada
Suzuki 2-Strokes: TC90, DS100

Re: New member with TC90 that dies in night mode

Post by singring »

I have not done the last set of tests yet, but following this link

viewtopic.php?f=29&t=8778" onclick="window.open(this.href);return false;

could very well be the same issue my bike has.
BTW in searching for a replacement NOS rotor for my Kokusan manufactured magneto,
they are hard to find...too bad it was not made by Nippon Denso, as there are plenty of those to be found.
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jabcb
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Posts: 4240
Joined: Mon Dec 13, 2010 4:32 pm
Country: USA
Suzuki 2-Strokes: 69 T350 thru 75 GT750
Location: southwestern Pennsylvania

Re: New member with TC90 that dies in night mode

Post by jabcb »

If you carefully go through the parts diagrams to figure out which parts need to be swapped out, you should be able to switch from a Kokusan magneto to a Nippon Denso magneto.

From a physics point of view, the alternators on the street bikes are much simpler than the magneto + alternator on the dirt bikes. To further complicate the issues, Suzuki used half-wave rectification and powered some components with AC.

Haven't thought it through completely, but the magneto relies on the ground voltage and problems with the alternator might cause AC leakage into the ground that messes with the magneto's performance.

Resistance checks might point to a problem with one of the coils, but you'll need to know the correct resistances.

Looks like an interesting problem deserving a little research.
BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 & 75
GT380 72
T500 69 project & 73 project
T350 69 & 71
Honda 85 CB650SC & 86 CB700SC
09 Triumph Bonneville SE
singring
On the street
Posts: 10
Joined: Thu Aug 29, 2013 6:02 pm
Country: Canada
Suzuki 2-Strokes: TC90, DS100

Re: New member with TC90 that dies in night mode

Post by singring »

I just did the second set of resistance checks....all show an open circuit(infinity) on my multimeter, there appears to be no wire or ground fault in the ignition switch or the wire harness. Definitely something going on from the magneto, as the problem seems to be isolated there, or wires from magneto. See again the previous resistance test I did on the wires from the magneto stator.....G/W to ground 0.1 ohms, Y/W to ground 0.1 ohms, B/Y to ground fluctuating 2.0 - 5.0 ohms. But, this would suggest that if the B/Y wire (AC voltage feed to the ignition coil) is grounding out somewhere, then the problem should also exist when engine is running in Day mode, which it doesn't. Baffling.
tunaglove
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Re: New member with TC90 that dies in night mode

Post by tunaglove »

I had the exact same symptoms and the cure was a new magneto rotor (the part with the magnets).
singring
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Joined: Thu Aug 29, 2013 6:02 pm
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Suzuki 2-Strokes: TC90, DS100

Re: New member with TC90 that dies in night mode

Post by singring »

tunaglove...yep, I read your posts about it, and your symptoms were EXACTLY the same as what I am experiencing with my bike. Trying to find a NOS flywheel right now. Thanks, glad I found your posts.
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