Bridgestone Motorcycle Parts Discussion Board
Bridgestone Tech Talk => 175 & 200 Talk => Topic started by: mybridgestones on March 17, 2017, 03:02:01 PM
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I have recently experienced some erratic behaviour on my HS 175 where it runs like a dream, then after about 15 miles it misfires, then starts popping and banging and suffers a total loss of power on both cylinders. At this point, it becomes unrideable and doesn't run properly again.
Now, everyone seems to have an opinion on this and one mechanic suggested that I check the ignition switch in case it has developed a fault.
So, my question is this: How do I temporarily hot wire the system to bypass the ignition switch? This is purely for testing purposes to rule out the switch as a potential problem.
Stuart
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Have you tried loosening the gas cap in case it has a blocked vent hole. Lets rule this one out before going further. Can't be much wrong if she will run 15 miles before playing up and that would use enough fuel to pull a vacuum on the gas tank.
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I' had exactly the same problem on my gto and after a lot of time and temper it was the fuel tank cap vent inside was a unseen rusted mess new one from Richard never missed a beat since in 500 miles
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I'd check fuel flow first, plugged cap is high probability. Also any restriction in fuel flow from tank to petcock to fuel lines. Any filters in the lines?
As to switch bypass: Run jumpers directly from the battery + side to the side of the coils that normally have 12v when the key is on and the points are open. (Sorry, I don't have a 175 handy to check wire colors, but if you disconnect all the wires going to the coils, you can check which wires have battery voltage when the key on.)
Another possibility is an overheating sparkplug due to, wrong heat range, or bad plug. It could be going bad when hot, but then recover once it cools off.
Good luck, I dislike intermittent problems the most!!!!!!!!
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(Sorry, I don't have a 175 handy to check wire colors, but if you disconnect all the wires going to the coils, you can check which wires have battery voltage when the key on.)
The wire feeding power to the coils is blue.
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Thanks for the replies,
It's a bit of a mystery this one.
It's had new HT coils, plugs, plug caps, battery, points, wiring loom and a bridge rectifier conversion. The generator was checked when the engine was rebuilt and the magnets remagnetised. All the electrical connections are good and the earth wires are secure.
When I experience the erratic running, I always unscrew the cap to see if there is a problem caused by a blocked hole, but it makes no difference. The tank is clear and the fuel is flowing freely. Also, the carbs are clean.
When it broke down the other day, the recovery bloke tested the battery and it was showing 12.75 volts, so charging is not a problem either.
My feeling now is that the condensors may be breaking down when they get hot, or perhaps a problem with the switch, which is why I wanted to rule this out.
It's taking some sorting out. The last three times I have gone out, it's broken down within roughly the same mileage.
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Stuart,
You have a real head scratcher here :'(,................. good to know other people get them !! ;D
Well at least it's consistent !! and does suggest something is heating up and then breaking down. I assume it will restart when things have cooled down. Definitely put new condensers in and see how she goes. ( the points may need checking/cleaning if condensors have been shorting) Never fully trust new items, they can be faulty, but two coils failing at the same time - unlikely. Consistent switch failure is also unlikely but never say never.
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Condenser and coils can both have temperature related faults. Have you been able to check spark while it was acting up?
If you have access to other coils andB condensers, I would try substitution, it can be an excellent way to find such intermittent issues.
Last year I spent a long time trying to figure out a spark problem with a little Honda. I first had a bad plug, and when I replaced the bad plug I also installed a brand new ignition coil. Bike would run for about 10 minutes and then start missing, getting worse till it almost stopped. As soon as it shut down and cooled off, it would run perfect again. After considerable frustration, I finally swapped the old coil back in, and it immediately ran perfectly!
I had bought a new, but defective coil!!! But since the coil was new, I assumed it just HAD to be good. I should have known better!!
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I will delve into it a bit more when I have time.
I'm actually going to fit the condensors externally so they will be easier to get to if they play up again. Apparently, they can be fitted anywhere along the line on the black and white wires.
Perhaps I should stick the old HT coils back on as well and see what happens.
The fix will probably be easy when I know what it is, but finding it.............
Will let you all know when I cure the fault so it may help others if they have the same problem.
Thanks for the input.
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Your problem obviously stems from something common to both cylinders and / or their respective electrical systems. Heat related failures of ignition systems over time can be traced to poor grounds in many cases. There will be enough ground to run when cool, but as temps rise, expansion occurs at the failed point, and ground is lost. Without the ability to ground, the points can't allow the coil the proper dwell time, and a misfire ocurs. I know that some of the smaller BS bikes use the ignition switch to control a ground circuit as well as a 6V circuit. If your ground side doesn't have good continuity throughout, you may be seeing the results. Try running a redundant ground wire from the battery to all key points such as switch, coils, and engine case as a test. You MUST have integrity and continuity on he negative side.
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Thanks for that information - What you suggest makes sense and I have actually cured the fault now by changing the condensors.
I didn't suspect these before because the points weren't showing any signs of burning. Also, the points and condensors were replaced anyway when the generator was reconditioned. That proves one thing - you can't take anything for granted with old electrical systems.
I actually made a little modification while I was it and placed the new condensors behind the battery. By doing it this way, they keep cool and are easier to access if they go kaput again.
I will upload a picture of the new layout one day and upload it up as a new post in case anyone else wants to do it.
In the meantime, thanks to everyone who offered help and suggestions.
Stuart
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Good diagnostic. Surprising that 2 failed together, but obviously a bad batch of product. Recently fought an intermittant no spark problem caused by some mild corrosion issues at a points contact plate on a BS90 Sport. So mild, I never would have suspected it, but that's all it was. Glad you're back in the saddle.
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Stuart, Great to hear you've sorted the problem, good result.
The popping and banging symptoms you originally mentioned suggested it could be an ignition fault, Ie, intermittent loss of spark which then ignites unburnt mixture in the pipes when she fires again. Unusual to hear of condensers failing to the stage where they stopped the engine. With both condensers being mounted on the same bracket, one failing would tend to heat up the other one, I guess. I've learned something new on this post.
Brian.