1984 T5 wont stay running

[Bob_Fla]

Strange condition
My 1984 T5 starts but does not run very long. The bike was not run for a few months.
When left alone for a time the bike will start with the choke on but stalls soon after. The bike runs for a 20-30 seconds, then dies.
I have gone through this many times. At first i suspected some type of fuel problem but after many times starting for a moment and then stalling I have found that soon after the bike starts, I loose spark. But there is definitely spark at first start.
The bike must be generating power/spark at first because it runs for a moment. But after the bike stops, I cannot get a spark.
Does this symptom sound familiar to anyone?
Thanks for any suggestions.

[cappisj1]

You can connect a timing light to the plug wires and verify that theory while it’s happening.

[guzzisteve]

Have to look at when last time the points were cleaned & set & timed. Stuff don't last forever on a 40yr old bike. Could be plug caps if still metal shroud type. OR just bad connection.

[Stretch]

Well, if there's a corroded/poor/loose connection somewhere in the ignition circuit,
it might work okay when cold, but when the hi-resistance connection heats up,
resistance increases and it acts like an open circuit. I might look there first.
Don't forget the ignition switch and the kill switch.

Or, your ignition coil(s) might be going bad. Failing coils can work okay when
cold, but then lose spark when hot.

                                                               -Stretch

[Offcamber1]

Bob, I think Stretch has you going in the right direction on this. I had a Lario from the same era, 1986, that did the same thing.  I ended up replacing the ignition switch and that was the end of the problem.  However, IIRC, you can remove the ignition switch, carefully pry the case apart, then clean up the contacts with fine emery paper and have a similar result to a replacement switch if the contacts are not corroded or burned up too bad.

BTW, the T-5 is a really nifty bike.  I had a chance to ride one once and really enjoyed it, but I guess I have a thing about 16 inch wheels.  (hence, multiple Larios...)

[Scout63]

I think it’s unlikely that you would lose both carbs or both coils at the same time.  Check power source to the coils and to the points, and grounds. If you still have the stock fuse box, check fuses.  Also ignition switch.  If you have other cutouts like a clutch or side stand switch, check those.

Also, check your fuel source.  Drop a float bowl and turn on the petcocks one at a time and see if the fuel keeps flowing.  I’m chasing the same problem on my 450 Ducati Scrambler.  I think I’ve got it pinned down to a faulty float needle.