Technical <G> light on a 650 engine

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Technical <G> light on a 650 engine

sheylings

Member
Joined
Dec 17, 2014
Messages
52
Hi

I have succesfully installed a 123electronic ignition into my 500, which has a 126 650cc engine. Took a while to realise that I was not differentiating between TDC of the two cylinders, but a quick swap of the HT leads on the dizzy and all is well.

I'm just back from a 10 minute drive, after which I retuned the carby - the 123 seemingly allows for a leaner mixture, potentially highlighting poor timing with the old dizzy. However, throughout the drive, the <G> light was always on.

I'm aware of Matt's Dad's very helpful sticky PDFs on all matters electrical, but I thought I would just ask for any input on any obvious failings I may have fallen foul of in replacing a dizzy that would cause the problem, in particular because I'm even less au fait with electrical matters than mecahnical matters!

Thank you all!
Steve
 

Bambino

Shed Troglodyte
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Aug 3, 2009
Messages
1,504
Location
Sunshine Coast, Australia
Changing the distributor should not effect the charging circuit.

Have a look around the engine bay and make sure you haven't accidentally knocked off a lead somewhere.

Chris
 

Vitesse

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Oct 26, 2011
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Westerham
Chris whilst you are on line!!!!!

I remember a post you did before that showed how you wired up the old voltage regulator stripped of its guts for an alternator conversion for a 650 engine. I have been searching around on the forum for it but cannot find it?

Can you remind me where it is?

Tony
 

Bambino

Shed Troglodyte
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Location
Sunshine Coast, Australia
Hi Tony,

Is this it (plus the usual alternator circuit)?

Chris
 

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MATTSDAD

New member
Joined
Oct 8, 2012
Messages
49
Hi Tony,

as Chris says you may have dislodged something in the engine bay.
With an alternator fitted, the Ignition light normally goes out at tickover or may flicker. Fitting an electronic ignition does not affect the battery charging circuit. Basically, the ignition light is connected between the battery and the alternator output D+ (or IGN) terminal (this is the thinner cable) which is the actual output voltage of the alternator. The "B+" Terminal on the alternator - (the thick cable) is the charging output and is the one that goes to the battery, so the alternator and the battery voltage will measure the same potential. If the alternator D output falls to less than 2Volts of the battery voltage, the ignition light will illuminate.
Check the voltage of the D+ terminal at tickover, it should be around 12V. Rev the engine and it should climb to about 14.5 Volts when the regulator should clip it at this voltage. If not, reasons could be
1) the fan belt is slipping
2) you have a poor earth on the alternator
3) the D+ (or IGN) output from the alternator is being shorted to earth.
BE VERY CAREFUL when working near the B+ terminal on the alternator as this carries the full power of the battery behind it.
Richard
 
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sheylings

Member
Joined
Dec 17, 2014
Messages
52
Hi Richard

Thanks for your help. I've taken various readings with ignition on, when ticking over and at 3000rpm. Results are below:

Ign on
B+ 12.2v
D+ 1.2v

Tickover
B+ 14.5v
D+ 11.3v

3000rpm
B+ 15.2
D+ 14.1

I'm not much or an electrician (or a mechanic for that matter!) and would be very grateful for your help.

Many thanks
Steve
 

MATTSDAD

New member
Joined
Oct 8, 2012
Messages
49
Hi Tony,
the alternator output looks OK.
Before we go any further can you check you have a good solid earth on the alternator. A lot of electrical problems are down to bad earths.
Make sure the alternator mounting lug is contacting nice clean shiny metal on the body and the fixing bolt and washer are also contacting clean body metal.
Matthew has the manual so I am flying a bit blind on this one.
Richard
 
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