Head scratcher
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If there’s a break inside you won’t tell by reconnecting it. It’d be the same
What colour is the plug?
Is the spark good?If you can’t dial in on the problem you’ll have to do a top end check eventually. Head off or at least check out the piston and rings through the exhaust port…
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I've rebuilt the top end, checked the ring gap all perfect new gudgeon pin and bearing too, it's running a brand new genuine yamaha coil right now. Is their any way of checking for a break with multimeter all the wires. Spark is perfect, but plug always comes out a little oily and black
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Oily and black is rich mixture. Probably where you’ve played with the needle/carb settings…
You won’t see a break inside the insulation.
I don’t know much about your model but it sounds like it’s rev limiting itself. If the wire (green?) isn’t properly earthed, or connected to it’s proper place (CDI?) the CDI might be defaulting to a ‘safe’ mode. I’ve heard of similar problems with bikes with the rev limiter read bulb in the speedometer…It’s the only thing I can think of if everything else is in good order like you said. It started off intermittent then failed completely…
You can do continuity testing with a multimeter. You may have to pierce the wire with a pin to make a testing point…
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Hey! Try running it with the ‘deristrict’ wire not earthed. See if there’s any difference…
The reed/read bulb refers to a dtr (don’t know what year) rev limiter…
PS have you cleaned out the jets and emulsion tube when you had the carb apart?…
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I've cleaned all the jets, but was wondering the emulsion tube refers to the press put large jet, that the main jet screws into, does that have some small holes going up the sides, I've only ever sprayed it with compressed air I've never removed it perhaps they may be blocked if they are present. I reconnected the wire yesterday and it made zero difference, I'll have a look to see if I have that read bulb. Thanks again @SpookDog
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@StanKn The emulsion tube is the long brass tube the main jet screws into yes. If you haven't done this yet you'll need to get this out (screw the main jet back in without the brass washer and lightly tap it), make sure all the holes in the tube are unblocked and also check its air feed is clear, this is the small clear tube which pushes onto a brass tube on the right of the carb body just in front of the carb-to-airbox rubber (it's a very small hole and difficult to blow through).
What happens over time is the space between the carb body and emulsion tube accumulates moisture and debris and this blocks more and more of the holes until it just starts fourstroking one day.
