Swapping parts may get expensive.

Wiring/connectors
How is the wiring between the headlight bucket around the steering stem to the rest of the bike? If the ignition supply wire is fractured here it can cut the ignition in an intermittent way. Try turning the handle bars while the engine is running .. if there are cutouts with the turning and none when the bars are stopped ...

Similar things can be done to check the rest of the wiring/connectors .. grab hold of them/it and flex it - pull and push .. if it cuts out while flexing and stable when not then ...

Weather?
Does it only happen when hot? Or raining?

Look for some commonality - only on rough roads, when raining, when the engine is hot/cold ...

Good Luck.

The culprit
 

Ladies & Gents,

In the name of completeness I thought I should report back with the elusive culprit. It was the ignition trigger, otherwise known as the bean can in the front of the engine, where on earlier models there were distributors. I was reading up on Robert Fleischer's site (Snowbum, the man who knows far too much), how there are several things which can cause strange intermittent electrical problems whilst the motorbike is moving:

1. Dodgy/dirty starter kill switch. Not in my case.

2. The coil, which either dies dramatically, or can sometimes die a slow death through a short circuit in the second coil. I replaced mine, but that wasn't the problem.

3. The bean can, the original of which is part electronic, part mechanical. A transistor inside of it called the Hall Device is the part which tends to fail, especially with temperature changes, especially when hot, while operating perfectly when cold. The cut in power can be just seconds, as was the case with me. He described it as a stumbling in the engine, which is exactly right.

Carlos Arias, a fine mechanic in Quito who also owns an R80 (a lovely miracle), came to the same conclusion and helped with fixing it.

So I bought the hopefully new and improved fully-electronic part made by Siemens from Motorworks, along with a new ICU (ignition control unit) which fits under then fuel tank, since they're replaced together. So far so good. It still stutters a bit when in 4th or 5th gears at low revs, but I think that's because the timing has shifted slightly and needs doubling checking, but it's no longer stumbling or cutting out.

Thanks all of you for your support. All the best,

Bob
Cali, beloved Colombia

The culprit
 

Ladies & Gents,

In the name of completeness I thought I should report back with the elusive culprit. It was the ignition trigger, otherwise known as the bean can in the front of the engine, where on earlier models there were distributors. I was reading up on Robert Fleischer's site (Snowbum, the man who knows far too much), how there are several things which can cause strange intermittent electrical problems whilst the motorbike is moving:

1. Dodgy/dirty starter kill switch. Not in my case.

2. The coil, which either dies dramatically, or can sometimes die a slow death through a short circuit in the second coil. I replaced mine, but that wasn't the problem.

3. The bean can, the original of which is part electronic, part mechanical. A transistor inside of it called the Hall Device is the part which tends to fail, especially with temperature changes, especially when hot, while operating perfectly when cold. The cut in power can be just seconds, as was the case with me. He described it as a stumbling in the engine, which is exactly right.

Carlos Arias, a fine mechanic in Quito who also owns an R80 (a lovely miracle), came to the same conclusion and helped with fixing it.

So I bought the hopefully new and improved fully-electronic part made by Siemens from Motorworks, along with a new ICU (ignition control unit) which fits under then fuel tank, since they're replaced together. So far so good. It still stutters a bit when in 4th or 5th gears at low revs, but I think that's because the timing has shifted slightly and needs doubling checking, but it's no longer stumbling or cutting out.

Thanks all of you for your support. All the best,

Bob
Cali, beloved Colombia