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The Vintage Japanese Motorcycle Owners Group: Discussion Forums

Vintage Japanese Motorcycle Owners Group :: View topic - TS90 weak spark?


TS90 weak spark?
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chuckin
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Joined: Jul 26, 2017
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PostPosted: Wed Jul 26, 2017 4:32 pm    Post subject: TS90 weak spark? Reply with quote

Hello everyone, new here, thanks for having me! So I'm trying to diagnose a weak spark issue with a 1970 TS90. Unfortunately, I don't know if the previous owner of this bike hacked it up. I bought it non running, and partially disassembled. I'm a carpenter, not a mechanic, so I've been struggling trying to get it running. I'm hoping someone here can help, it's a nice bike and should clean up well. But first things first...

I actually just bought an extra parts bike, figured I'd take my chances for 100 bucks. I swapped the points plate/magneto after cleaning, and still have the same results. I'm suspect of the external ignition coil, so let's start there. I tested the resistance but I don't know what the readings should be. I came up with 2.6 ohms on the primary side, and 8.14k on the secondary. Do these numbers sound good or bad? Thanks in advance...
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dorT500
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Location: Galveston County, Texas

PostPosted: Wed Jul 26, 2017 5:16 pm    Post subject: Re: TS90 weak spark? Reply with quote

chuckin wrote:
...........I came up with 2.6 ohms on the primary side, and 8.14k on the secondary. Do these numbers sound good or bad?
As far as the numbers go.....they are good. Welcome to the VJMOG and maybe this will be some help on any other issues you are having. http://www.ozebook.com/compendium/suzi/suzidata1.htm Page 15 Should be a pdf service manual link around these forums somewhere. There several members here that should be able to help also.

http://www.ozebook.com/compendium/techbuls/

Good Luck and again Welcome to the VJMOG

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dorT500
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PostPosted: Wed Jul 26, 2017 5:57 pm    Post subject: Reply with quote

Here is a pdf service manual if you need one. http://suzukits.informe.com/wiki/view/Index_of_documents
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chuckin
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PostPosted: Wed Jul 26, 2017 6:27 pm    Post subject: Reply with quote

Excellent information thank you! Admittedly, a lot of it is overwhelming to me, but I'm learning. So, I was suspicious of the points plate on the bike because there was a frayed wire (that I fixed) and it appeared that a poor soldering job was done on the top of the condenser. I had planned to order new points and condenser, when I happened onto the parts bike. Although old, the system appeared completely intact. So I swapped the entire thing, after cleaning everything up of course. Does it seem possible to have swapped one bad condenser, points, or coil for another? Or is it more likely that I need to work on the timing (which I'm unfamiliar with) thank you for the response.
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chuckin
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PostPosted: Thu Jul 27, 2017 4:34 am    Post subject: Reply with quote

Thank you so much for the information. I will pick up some feeler gauges and try to adjust the timing. Do I need a special tool to find the 20° BTDC? I feel like I can eyeball that, but is close good enough? If someone could guide me through the process of diagnosing the weak spark in layman's terms I would very much appreciate it. It's all new to me, probably a simple process for most of you. Everyone had to start somewhere right? I'm confident that I tested the external coil properly, what would be the next test I can do with my multimeter, or is there one? Is the timing critical to producing a strong spark? Or just when that spark occurs? For example, is that my next step, or the final step after I get spark? Thank you!
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spurlock
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PostPosted: Thu Jul 27, 2017 7:12 am    Post subject: Reply with quote

Greetings Chuck,
Sounds like you have a nice bike there. First off, what are you seeing exactly in the way of weak spark? When in dim light, with a new spark plug laying on the cylinder head and connected to the coil wire, kicking the engine over fast you should see a fat blue spark. Yellow or faint spark would be weak.

First check that the points are clean. Even a tiny bit of lint or grease can cause weak or no spark. Thin wet/dry 320 silicone carbide sandpaper doubled over can be used to dress the surfaces if needed, followed by spraying with electrical contact cleaner and compressed air.

Next, yes the ignition timing does affect spark strength, since the ignition primary coil is energized by the flywheel magnets which produce AC current. That alternating current must be at maximum when the points open in order to send maximum power to the main coil and fire the plug. Turn the flywheel until the points are at their widest opening, then set the points gap to .014" +/-.

Then confirm that timing is correct: Unplug the black/yellow wire coming from under the flywheel and connect one lead of your ohmmeter to it and the other to ground. When the points are closed the needle should show continuity. Rotate the flywheel slowly in the running direction while watching the meter. When the points open the needle should drop to zero. That should happen when the timing mark on the flywheel aligns with the index mark on the engine case. The mark is probably stamped with an "F". If timing is too early, decreaase points gap slightly and visa versa until timing is correct.

Other potential problems are bad spark plug, bad resistor cap (take off and connect the plug lead directly onto the spark plug to test), and loose/dirty connections in the ignition circuit. Clean and tighten all connections. The ignition switch grounds the black lead when the key switch is off, so corrosion inside the switch could be partially grounding the ignition when the key is on. Unplug the black/yellow lead from the key switch to test.

Good luck and let us know how you make out.

-Bill

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1975 Honda XL250K2
1989 Honda NX250
1989 Honda GB500tt
1990 Honda GB500tt


Last edited by spurlock on Thu Jul 27, 2017 9:07 am; edited 1 time in total
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chuckin
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PostPosted: Thu Jul 27, 2017 8:31 am    Post subject: Reply with quote

Very informative thank you. Yes she is nice, not mint by any means, but quite worthy of attention. I tried to post a pic but I think the format size was too large. I don't have a home computer, doing everything from my phone. I will get pics up eventually.
Anyhow, faint yellow to almost non existent would be my best description of the spark. If I hold the plug while I kick it will give me a small zap, but not strong enough to even jump the spark plug gap. If someone wants to confirm the exact plug gap I should use to test that'd be great. I did clean the points, but was worried to do too much, not knowing how much can be taken off while not ruining them. I also don't know if anyone else has already sanded on them, or how much, so I was being cautious. I will follow your instructions and see how it goes. And of course post questions as they arise. Thank you so much for your help everyone!
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spurlock
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PostPosted: Thu Jul 27, 2017 9:11 am    Post subject: Reply with quote

Chuck, I corrected an error in my post in the paragraph about checking timing using your ohmmeter. On the points, the only reason to sand them is to make sure they are clean and free of corrosion. Sounds like what you have done is fine, as long as there are no bits of paper left between the surfaces.

You're a brave man to hold the plug while cranking. With good spark you would never try that twice! Good luck

-Bill

_________________
1975 Honda CB125S
1975 Honda XL250K2
1989 Honda NX250
1989 Honda GB500tt
1990 Honda GB500tt
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chuckin
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PostPosted: Thu Jul 27, 2017 11:00 am    Post subject: Reply with quote

OK very good...haha! That actually happened by accident, but confirmed to me that at least something was happening. I will heed that warning for sure! Hopefully next time I'll have a visible spark...and now I'm scared...
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chuckin
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PostPosted: Sun Jul 30, 2017 4:46 am    Post subject: Reply with quote

Well...I repeated the steps a few times with both points plates and nothing. I found myself putting way too much focus on the one off the parts bike, as it all looked factory and not tampered with by a second party. (Or 3rd, 4th, etc.) I put the old one back one last time and adjusted the points and WHAM!
Got a nice and consistent spark! Put the plug in and WHAM! She fired! So, after a bit of reassembly, I took her for a short ride. Not bad, other than the lights, everything seems to work as it should. Cleaned the carb, gas tank, petcock. New fuel and air filter. So I began to put this thing back together, I had a lot torn apart, and the previous owner had parts missing and torn apart everywhere. With each part I reassembled, I'd start it up and adjust as needed. By the end of the day, she looked very nice, and would sit and idle nice too. After cleaning up the giant mess in my driveway, I went to put it away for the night. And she died on me. And wouldn't restart. I'll get it back out today, hopefully it's something simple this time. As long as it has spark...fuel delivery I can handle! Thanks a lot for the help guys, I'll keep you posted...
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chuckin
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PostPosted: Sun Jul 30, 2017 7:20 am    Post subject: Reply with quote

No spark again...
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spurlock
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PostPosted: Sun Jul 30, 2017 9:01 am    Post subject: Reply with quote

chuckin wrote:
No spark again...


To eliminate a short or partial short to ground in the key switch, unplug the black/yellow wire at the switch and see if your spark returns. Also using an ohmmeter, check the black/yellow wire from the points to the coil for breaks inside the insulation or bare spots that might be grounding out. Wiggle and stretch the wire while testing.

-Bill

_________________
1975 Honda CB125S
1975 Honda XL250K2
1989 Honda NX250
1989 Honda GB500tt
1990 Honda GB500tt
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chuckin
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PostPosted: Sun Jul 30, 2017 9:39 am    Post subject: Reply with quote

I have the black/yellow wire from the points connected directly to the exterior ignition coil, and the coil to solid ground. Getting ready to check the wires as you mentioned...I don't think I have the points right though, it's a bugger getting in there with the magneto on.
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kbts250m
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PostPosted: Tue Aug 01, 2017 10:43 am    Post subject: Reply with quote

If I had a good spark that then quit I would suspect a loose connection or pinched wire in the magneto or between the magneto and coil. Easy to check with your ohmmeter. Remove spark plug and unplug the black/yellow from the ignition coil and check that wire to see if you have continuity to ground. If so, the resistance should change as you turn the rotor and the points open and close. If no continuity whatsoever you have an open circuit (loose or broken wire) and if continuity all the time with little or no resistance you have a pinched (grounded) wire.
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chuckin
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PostPosted: Sat Aug 05, 2017 4:41 pm    Post subject: Reply with quote

Ok...I will be back to wrenching tomorrow. Thanks for the help, I will post updates tomorrow on the progress...
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