At About 20 Miles The Bike Shuts Off

Ahything electronic can fail if it gets hot. ...J.D.

 

Blocked fuel tank vent? Try opening the filler cap next time and waiting five minutes.....

 

Has the tank been taken off? Could be a kinked fuel pipe. Try running the bike in prime position to see if it helps but don't forget to turn back to on position afterwards. CPS usually fail when the engine is hot and will start when cold again.

 

Is the battery getting a charge?

 

Sounds more electrical to me. A fuel issue usually starts with some stumbling or sputtering, THEN quits. Electrical either works or it does not, so when it is off, it is off. Just an observance from an ancient, old mechanic. Of course, if you have EFI then ...J.D.

 

Have you got, or can you get, a wiring diagram?
Personally I would bypass all possible sensors ( thinking side stand, clutch lever etc) with a small jumper cable and see if the problem is resolved.
If it appears to be, then reintroduce one connection at a time until the problem reoccurs.
Bingo

 

I will relate an experience I had with my 95' Sprint because it is uses the same chassis. The main electrical feed from the main fuse comes up the right side of the frame on it's way to the kill switch, and is anchored to the steering head on a small lug welded to the frame. On mine, after years of use, it cracked the insulation. I chased it for a long time until it finally blew the main fuse. Only then could I find it using a meter. I detached the wire loom from the lug to give the wire a bit more slack, and fixed the broken insulation. Probably not your problem, but a side note on the old T-3 chassis to keep in mind. ...J.D.

 

My bonny does that after about 4 miles. Could be the coils heat up. I got new coils I am going to install. Feel them to see if they are getting hot.

 

My bonny does that after about 4 miles. Could be the coils heat up. I got new coils I am going to install. Feel them to see if they are getting hot.

 

They are going to generate some heat, just from doing thier job. It did not help that Triumph installed cheap coils to begin with, and placed them right over the cylinder head where they will cook to a golden brown. Ambient temp here in the Mojave Desert in the summer is well over 100 all summer long. Get stuck in some traffic and things get a bit warm. Some guys update them to the later style "coil packs", but that can be expensive. ...J.D.

 

It's unlikely the coils would overheat and quit at the exact same time.

 

This is true, but when the internal insulation starts breaking down, it can make the engine run bad enough it will quit. I have been through this on both my 3 cylinder T-3's. As soon as I replaced the coils, the problem was gone. I don't know if the primary side was shorting out internally or what. So far, my '02 America has not suffered from this, but I bought it used. I don't know if the coils have been replaced on that one. Of course, I am not saying this is the only possible cause. ...J.D.

 

That one is electronic, for sure, but that sounds more like something that affects all the cylinders. That would be the low voltage side of the ignition. Crank sensor is a possibility. Something in the ignition key circuit. One of the kill switches acting up. Lots of possibilities there. Time to get out your meter and have a heart-to-heart with it. Sometimes you never find it till it quits completely. Intermittent electrical issues are a pain. ...J.D.

 

This fault on an old bandit was sorted by changing coil packs

 

I don't know if this will help diagnose but I was watching this video recently where he had a faulty crank position sensor. He has a novel, to me, way of testing the sensor with a heat gun. It was reading normal around 560ohms cold, but as he warmed it up its resistance varied a lot and then it failed. He then let it cool and it returned to normal.

 

Looks more like destructive testing to me. Any electronic device will fail if subjected to enough heat. I do not see that this proves anything we did not already know. ...J.D.