Reading Heinz's post on Sigma 1.6 issue, soft but continuous dropouts
reminded me of a similar issue I had with a Suzuki GS1100 sidecar outfit.
I bought the outfit specifically to do a very long trip but it had been standing unused for a long time and was not in the best of condition however the engine seemed fine. The first long trip I did with it was to the Easter bike races at Bathurst (200km West of sydney). By the time I arrived I was getting very erratic running of the engine which I put down to dirty jets in the carburettors. The GS1100 was a carburettor model so it was nothing to do with fly-by-wire or fuel injection. Accordingly I pulled out my tool kit (one of the advantages of a sidecar) and dismantled the carburettors. To my astonishment I found the float bowls had a layer of dirty jelly like substance in the bottom. I cleaned them, made sure the jets and filters were clean and reassembled the lot. In time I was to become expert at tuning and balancing 4 carburettors by ear
All seemed reasonably OK until I had started out on a long trip of nearly 10,000 km: Sydney, Melbourne, Adelaide, Uluru, Alis Springs,Mount Isa, Bourke, Brewarrina, Dubbo and back to Sydney. At one point I pulled into a remote farm house and borrowed an empty fuel drum from the bemused farmer's wife and drained and flushed the fuel tank. She offered us tea and scones, which we accepted, and finally some fuel if we needed it, which we did not as I had a 5 litres can spare.
Absolutely nothing worked and I became convinced the fault was in the ignition ECU. The ECU was exposed as the left side cover had been removed to fit the sidecar. I had unplugged and replugged the ECU several times thinking it could be a dirty contact. At a certain point it started playing up again just as I was leaving a service station. In annoyance, without turning off the engine, and whist still moving, I reached down and unplugged the cable from under the ECU and shoved it back in again.
The engine stuttered and then began to run smoothly and never gave any further problems. I think I probably caused a spark which was just enough to resolder a dry joint inside the ECU.
I don't think I could recommend this as a course of action however as I am sure it would be more likely to do damage than fix it