72 T500 Electrical Problem - No Spark To The LH Plug

[Syd]

I would appreciate some help with the above problem. I have just completed a ground up restoration of my 72 T500 J and she is looking really nice. I started the bike this weekend, however only the RH side cylinder is going. Everything electrically on the bike works fine (all lights, flashers, horn, brake lights, neutral and instrument lights etc)

Most items have been replaced with NOS parts including a new wiring loom, coils, rectifier, flasher relay, points, condensers, plugs, plug caps, battery etc. I rechecked all of the wiring loom connections and plug fittings.

I measured each coil and they are both around +4.2 ohms and the voltage at each of the points is approx +12.4v. Maybe the coil for the LH is faulty. The coils were supplied by GT Reiner. All the ground points have been rechecked and are fine.

Any ideas on how to solve this problem would be much appreciated.

[jabcb]

For the LH points, check the wire attachment point. You may have the parts in the little stack of insulators + washers + wire connector in the wrong order. There also needs to be an insulator covering the threads of the screw that holds this little stack together -- when assembled you can not see this insulator.

Other voltage to check that might point to problem:
- voltage drop across coil primary with points open & closed
- voltage at points with points open & closed

You can run temporary wires so that RH points+condenser connects to other coil+wiring.
And do same for LH points+condenser.
This will show if problem is before or after where you run the temporary wire.

[titan performance]

Presumably there is no spark at the plug?
Were the condensors replaced?

[Syd]

All the small parts making up the points fasteners, washers, spring washers, insulating washers and insulting tubes are correctly fitted.

The voltage at the points with the points open and/or closed is the same = approx 12.4V

Voltage cross the coil primary - can you clarity how to check this? One coil has a black wire going to one set of points and the other a white to the other set of points. Both coils have orange wires going to the main harness. Do you measure from the black or white points on the coil to ground to check the voltage?

Change coils around - I have connector plug terminals on each of the black and white wires going to each condenser, I assume if I swap these around, this should do the required check?

[Syd]

Jabcb - To answer my own earlier question, yes, when I change the connector plug wires from each coil around prior to the condensers on each set of points, I moved the problem over from one coil to the other which tells me that the LH coil is faulty. I changed them back again and the problem moved back to the LH side with no spark at the plug.

[Alan H]

The voltage at the points with the points open and/or closed is the same = approx 12.4V

The voltage at the points when they are closed should be zero, otherwise the points aren't closing.
Sounds like a points/wiring problem to me, not coils. The fault moves when you change the wires to the points doesn't it?
It can't be the coil as each one fires when it runs on the 'good' set of points.
Check that the points actually close on the side that doesn't fire. If they don't close, then they can't 'open' and it's the act of the points opening that caused the spark.
Make sure the gap is set correctly, if it's too big, that may be the problem.

[Syd]

I understand your point and I will double check this again and report back

[jabcb]

+1 on checking to make sure the points actually close.
The points might need adjusting or there might be some "crud" on the contact surface preventing an electrical connection when the points close.

If that doesn't solve the problem, check the little stack of parts where the wire attaches to the points.
It is possible to arrange the parts so that the wire is insulated & has no electrical connection with the points.

[Syd]

Thanks for your comments. Just a question about this as I am puzzled about the actual stack design as you have a small insulated centre tube for the screw plus two insulated washers either side + normal washers either side and then the nut and spring washer. When assembled correctly with the condenser pigtail fitted - the condenser wire is completely insulated from the points, therefore how does this work?

[jabcb]

See this topic for a points diagram.
search.php?keywords=insulator&terms=all ... mit=Search" onclick="window.open(this.href);return false;

[Syd]

Thanks - all understood. Will recheck this and the points closing again today

[Alan H]

See this topic for a points diagram.
search.php?keywords=insulator&terms=all ... mit=Search" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

Not noticed that before and it certainly saves trying to describe the connections jabcb.
The two insulators are like small top hats so they can't move and allow the bolt to touch the mounting bracket.

[Syd]

Yes, it does seem that the LH points contacts are not closing correctly which will explain all of this. I will reset the points and hopefully she will be up and running - thanks for all the help.