Mornin’ Laurie et al...
Possible I suppose it could be a vacuum leak bearing in mind your bike has about a metre more vacuum line than most given the MC cruise setup, so worth a look. Mind you I found that when mine had perished it had no noticeable effect on engine performance, its effect was limited to the MC cruise failing to hold. Also, it is odd that if it was vacuum patency that was causing the problem why is it intermittent and only after periods of seemingly satisfactory engine running. I would have thought a failure of vacuum to supply adequate fuel would be continuous, so here’s another thought;
Electrical.
Apart from superstition that there is an electrical gremlin already wired into your wiring harness
I believe that the cause of the problem you describe is to do with the impulse generator and / or the it’s ancillary component(s). Here why.
If memory serves me, you still are using iridium spark plugs. I use iridium spark plugs in my bikes that have magnetos as their source of power for ignition, rationale is magnetos though highly efficient they are also high maintenance and it either points or contact rings foul (corrode), the energy they produce drops off rapidly and thus spark at the plug also drops off to the point my old English bikes either won’t start when hot (
key point), or will run rough at speed. The iridium plugs in part largely offset the steady deterioration of corrosion to points and contacts within the magneto as they (the iridium plugs), are far better at producing a good spark from a wider parameter of received energy from the ignition source.
An example of this can be seen in aviation. Before any flight of an aircraft fitted with a reciprocating engine one part of a pre-flight check consists of an engine run up during which the magnetos (reciprocating aircraft engines are fitted with duel ignition systems), are check. Essentially depending of engine type and variant the engine is brought up to say 1250RPM and with the fuel mixture at full lean and after the engine has reached its operating temperature, first one magneto is switched off and then the other and during each time one of the mags is switched off a drop in engine RPM is noted. However, if an RPM drop is noted that is below accepted parameters (usually >200-250RPM), and before it is switched back on,
if the mixture is pushed in to richen the fuel mixture you can (at times), elicit and increase in engine RPM, which tells you the ignition (magneto), is in need of attention. Beginning to sound familiar?
I have only ridden one ST1100 that has needed to have its impulse generator replaced and at that time my money too was on a fuel issue, but Honda MPE proved me wrong.
One way Laurie you could test this theory is if you have any of the original spark plugs floating about your shed, fit them and see if either (a) you can start the engine or, (b) the problem is manifest at a much earlier time or temperature or distance travelled.
Or to quote a phrase from Star wars, “
look for the source Laurie, look for the source!”
Just a thought.
Ciao, the can :)
