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Voltage to auto choke disappearing under load


junkman
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Hi everyone, I have an odd issue where I can measure 11 volts across the plug for the auto choke when the unit is disconnected, but when I connect it the voltage disappears. I've tested the auto choke direct to the battery and it works fine.


There seems to be an issue on the ground side. The 'negative' wire (grey) goes to the CDI, and the CDI then has a separate wire to ground (blue).


With the auto choke connected, I can measure voltage between positive on the choke, and blue on the CDI, but not when I switch to grey on the CDI. And yes, there is continuity between grey at the CDI and auto choke ends.


If there's any electrical experts out there who can weigh in I'd be super grateful, cheers!

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Can you be a bit more descriptive......ie, where you are measuring, between which points?

Which wires is the autochoke getting its positive feed?

The CDI is likely to control it with a switched negative.

Also.....11v sounds a little low to me......so, if there's some kind of resistance in the wiring or connectors, it could be enough to kill the voltage when the circuit tries to draw some current.

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Cheers Tango, the positive to the autochoke is effectively direct from the battery (via the 7.5a fuse and ignition barrel only).


The grey wire described is the negative from the autochoke connector, which goes to the CDI.


With the autochoke disconnected I measure around 11 volts across its connector.


When the autochoke is connected I get no voltage across its connector, and also none if I measure between positive at the connector and the other end of the negative wire (grey) at the CDI. But if I measure between positive at the connector and ground (blue) on the CDI, I do get voltage (I hope that's clear but I can post the wiring diagram if not)!


This seems to me to isolate the fault to the grey wire - I tested to see if it was shorting to any other of the wires going to the CDI, by disconnecting the CDI plug and testing for continuity between grey and each other wire in turn - I didn't find any though.

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Just to clarify. .....are you measuring the voltage between the frame and the Grey wire? With the autochoke disconnected you're getting 11v on the Grey wire when measured to ground.....but the voltage disappears when the autochoke is reconnected?

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When you connect a wire to ground that will drag its potential down to ground and all voltage appears to disappear, and that is not in itself a fault, I think you need a specialist to diagnose this.


I don't enough other than to caution against drawing conclusions at this time.

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Sorry for disappearing for a few days...


Tango, I wasn't measuring between the frame and grey, no. They'd be one and the same, wouldn't they? Both negative/ground? I measuring between grey at the connector and positive at the connector.


Griptwist, you may be right. The original issue was that the autochoke didn't seem to be working. I took it out to tweak the extension amount on the needle and couldn't get it to work at all. I decided to do without it for now and put it back in the bike, and now it's working. Sods law! Must have a dodgy connection somewhere.

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Sorry for disappearing for a few days...


Tango, I wasn't measuring between the frame and grey, no. They'd be one and the same, wouldn't they? Both negative/ground? I measuring between grey at the connector and positive at the connector.


Griptwist, you may be right. The original issue was that the autochoke didn't seem to be working. I took it out to tweak the extension amount on the needle and couldn't get it to work at all. I decided to do without it for now and put it back in the bike, and now it's working. Sods law! Must have a dodgy connection somewhere.

 

I'd say from your description that the grey wire is the control signal from the ECU.......It will switch to ground When the autochoke signal is active, ie, when the ECU is calling for autochoke. Otherwise, the grey wire will likely be at +12v.....so if you measured between the 12v supply and the Grey wire it will show 0v, as both wires would be at the same potential. It's only when the ECU activates the autochoke control that the grey wire would go to 0v, at which point you'd be able to read 12v between the +12v supply and the Grey wire. I hope that this makes sense?..... 8-)

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Cheers Tango, what you're saying does make sense, except - why does it need a control signal? As far as I knew autochokes were just on all the time - you turn the bike on, they heat up over the course of a couple of minutes and then they're engaged until you turn the engine off. Have I got that wrong?

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