No spark to plugs.

[cephas1981]

1979 R65.  So my engine has been sporadic at starting lately and wouldn't start the today.  After checking all the connections and running a couple tests I thought it would be the ignition trigger unit.  I uncovered the front of the engine, gave it a couple taps, connected the battery back up and it fired up.  I then unhooked the battery again and took the ignition trigger unit off.  I opened it to find water had gotten in and some rust was floating around.  I took off the bracket and took out the contacts.  I cleaned it, put it back together and tested it with a voltmeter continuity and the contacts were working.  After re-installing it on the bike and reconnecting the battery I tried again to start it....no start.  I tested the coils and they check out 11.xx on the voltmeter with the key on, negative ground and positive on #15 on the coils.  There is just shy of 12V on the battery.  I pulled the plugs and will not get a spark.  I may have put the ignition trigger unit back together wrong but there's only one way it will go back together.  I'm at a loss as to what exactly is the problem.  If pics would help, I can get them for you.  

[Sergeant_Joe]

Battery should read higher than 12v  .
13.5 v is good, if only 12v it will drop to below 8v or so when you hit the starter button.
I take it it is points, have you set the gap to wide for this weak spark to jump?.

[cephas1981]

Do you mean the gap on the plugs or the contact points in the ignition trigger unit?

[Sergeant_Joe]

Both!.
However I would be more sus of the low battery reading, if my bike gets down to just 12 volts it's hard or no start time .
Do you have stock coils? if so they can crack and drain off extra power, I had this happen so I replaced it with two Bocsh GT-40 coils, all good after more than a year .

[Barry]

Yours is a standard for 79 model points in the can ignition unit  like the simplified wiring diagram below. Right ?

A good test for the points ignition is to pull the black wire off the connector on the bean can.

With the ignition on you should measure approx. 12 volts between this wire and earth. If you don't read 12v then there is an open circuit fault somethere in the wiring or one of the coils.

If you have 12 volts briefly short this wire to earth and when you release it the plugs should spark. If they do the fault is with the points but you already checked those with an ohm meter so maybe a short circuit on the condenser. [img][img]

[cephas1981]

Looks like it.  I'll give it a shot tomorrow after I make sure there's at least 12 v in the battery.  It wouldn't surprise me that it would be the trigger unit.  Even though it checked out for continuity it doesn't mean that's not the issue after all.  Joe, I highly doubt it's the coils.  They are old but why would both of them go out at the same time?  It's got to be something that sends power to them and I have a couple newer spare coils I tried and they didn't even work.  And I'm not sure about the gap in the trigger unit or the "can".  From what I can tell, as the shaft rotates inside the can, it pushes the contacts apart then they come back together.  Do they need to be a certain distance from each other when they're pushed apart?  There is one place where the shaft comes in contact midway down the arm that's directly attached to one of the contacts (the arm that gets pushed by the shaft).  Does the shaft and that arm need to be continually touching or should I back the arm off and leave a gap there and if so, how much of a gap?  The diagram looks accurate Barry.  Thanks for putting it up here.  I know this is long guys but I just want to be as accurate as possible.  Thanks for the advice.

[Barry]

Do they need to be a certain distance from each other when they're pushed apart?

Yes the points gap should be .016" when they are fully open. In terms of getting the plugs to spark, the gap is not ultra critical a couple of thou either way although if it is much too small the plugs may not spark at all as the arc created when the points open will not be extinguished.

It's a bit tricky to set the gap with the end bearing plate in the way but beware if you set the points without the bearing plate in place the gap will change when you put it back on. I find it much easier to remove the whole bean can when setting the points so I can see what I'm doing. It does mean you have to check the ignition timing again afterwards but you should be doing that anyway as adjusting the points gap will always change the ignition timing slightly.

I highly doubt it's the coils. They are old but why would both of them go out at the same time?

It probably isn't the coils but because you have two 6 volt coils connected in series if one is faulty as in open circuit you loose the spark from both of them.

[cephas1981]

I adjusted the gap on the contact points.  The bike"s back up and running.  Thanks for the advice.