73 Commando, No spark.

timarl54@yahoo.com · Dec 18, 2016

Well here is another "No Spark" problem.. I'll try and be coherent. Restoration near completion. Have new fully charged battery, original 6v coil/ point ignition, rebuilt handlebar switches, new points, plugs , condensers, original wire harness in excellent condition. Bike ran before complete tear down. Lights, horn, turn signals and brake light all functioning properly. I have power (white) to handlebar switch and power out on white/ yellow to white/blue to resistor and out white/purple to coils. here is where im stuck. not sure what to check next. Any input will be appreciated. Thanks

L.A.B. · Dec 18, 2016

Check the points wire ring terminals are correctly fitted between the spring and nylon insulator and that they are not between the insulator and the nut (which grounds the wire).

timarl54@yahoo.com · Dec 18, 2016

That was it!! Thanks, ignition is not my strong suite, Thanks to you i'm learning. Thanks again. I have about 4 month to dial it in before weather allows a maiden voyage.

L.A.B. · Dec 18, 2016

timarl54@yahoo.com said:
That was it!! Thanks, ignition is not my strong suite,

It's an easy mistake and you're certainly not the first person to have done it! :wink:

gripper · Dec 19, 2016

There is no reason not to persevere with points but it's well worth strobing the timing. The backlash in a worn advance retard unit and general slack in the points system can lead to a massive timing error. It cost me a cracked piston on day two of Commando ownership 41 years ago. Once set by the book method, you can expect to see the timing at 40 degrees of advance when you strobe it and if your ankle survives first contact with the enemy :cry:

MikeM · Dec 21, 2016

L.A.B. said:
Check the points wire ring terminals are correctly fitted between the spring and nylon insulator and that they are not between the insulator and the nut (which grounds the wire).

This is what LAB suggested to me when I had the same issue. It worked for me also . Thanks LAB

Rohan · Dec 21, 2016

Re: 73 Commando, No spark. WARNING !!!!

gripper said:
Once set by the book method, you can expect to see the timing at 40 degrees of advance when you strobe it and if your ankle survives first contact with the enemy :cry:

WARNING WARNING WARNING
The correct timing advance before Top Dead Centre TDC is 28 degrees, fully advanced, according to the book.
( Part C38 in the Commando Workshop Manual for 1973)

Strobing to 40 degrees would probably see the pistons melting and flowing out the exhaust pipes before too long...
LAB might like to correct the above, before someone destroys an engine...

Fast Eddie · Dec 21, 2016

Re: 73 Commando, No spark. WARNING !!!!

Rohan said:
gripper said:

Once set by the book method, you can expect to see the timing at 40 degrees of advance when you strobe it and if your ankle survives first contact with the enemy :cry:

Click to expand...

WARNING WARNING WARNING
The correct timing advance before Top Dead Centre TDC is 28 degrees, fully advanced, according to the book.
( Part C38 in the Commando Workshop Manual for 1973)

Strobing to 40 degrees would probably see the pistons melting and flowing out the exhaust pipes before too long...
LAB might like to correct the above, before someone destroys an engine...

Grippers is simply suggesting that even by setting the ign 'correctly' according to the manual, worn components in the advance retard mechanism can lead to an actual advance figure being very different, hence his advice is to check it with a strobe.
What needs correcting?

Rohan · Dec 21, 2016

Re: 73 Commando, No spark. WARNING !!!!

From just a casual reading, thats not entirely obvious ?
Especially for a commando newbie looking for some numbers to set the timing to. ??

Having worked in a technical business, if it can be read wrong, it will be done wrong. !!
Ask me how I know this....

Now, if he'd said the correct timing was 28 degrees, and with wear it can be as far out as 40 degrees btdc...

There is also the minor matter that the manual mentions turning the motor backwards to set the timing.
That in itself can be a bit of a no-no, if all the backlashes can accumulate.

Fast Eddie · Dec 21, 2016

Re: 73 Commando, No spark. WARNING !!!!

Rohan said:
From just a casual reading, thats not entirely obvious ?
Especially for a commando newbie looking for some numbers to set the timing to. ??

Having worked in a technical business, if it can be read wrong, it will be done wrong. !!
Ask me how I know this....

Now, if he'd said the correct timing was 28 degrees, and with wear it can be as far out as 40 degrees btdc...

There is also the minor matter that the manual mentions turning the motor backwards to set the timing.
That in itself can be a bit of a no-no, if all the backlashes can accumulate.

IMHO you are 100% correct... from a technical writing perspective.

But this is an Internet forum Rohan, not even Lab can possibly proof read and correct every post to that level!

Neither is it the purpose of such forums.

Danno · Dec 22, 2016

I remember reading when Boyer came out with the EI for Britbikes that timing could be advanced to 32 deg BTDC with electronic ignition and that the 28 degree figure allowed for mechanical imprecision of the stock points/mechanical advancer.

L.A.B. · Dec 22, 2016

Re: 73 Commando, No spark. WARNING !!!!

Fast Eddie said:
But this is an Internet forum Rohan, not even Lab can possibly proof read and correct every post to that level!

Neither is it the purpose of such forums.

I read it as gripper intended so I didn't see any reason to say or do anything.

73 Commando, No spark.

timarl54@yahoo.com

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