I am experiencing a long-standing intermittent problem on my '93 R100R. I finally am concerned enough to dive into this as time permits, and I'd appreciate any suggestions for possible causes and potential resolutions.
The problem I'm having only seems to exhibit itself during long trips, meaning after several consecutive 500+ mile days. I'll be running along at speed and the bike will lose power. It feels as if it were running out of gas, however switching to reserve has no consistent effect. The bike will slow to 65 or 60mph and maintain that speed, even thought the throttle is fully open. It's running poorly during this, feeling and sounding bogged down. After a mile or so, full power resumes. It may or may not happen again in a few miles. This has been an occasional but ongoing problem for 3 or 4 years now.
I've always assumed the issue was fuel-related because it invariably seems to happen in the Midwest (high-alcohol fuel, 2 days from where I live); because it usually happens 10 to 12 miles into a new tank and again 60-80 miles into the same tank; because last year it occurred just after I had to remove the cross-over fuel line due to a leak as I passed through KC; because when power resumes there is no back fire (which to me would indicate an ignition problem allowing the fuel to load up). I've tried lifting the tank bag (RKA bag with plastic bottom) up off the gas cap when the problem occurs, and it has no affect.
I use this bike for weekly grocery shopping (local, non-highway) and touring. This season I took 2 trips: a 5-day Georgian Bay circumnavigation (2500 miles) and a 7-day journey to the Return to Shiloh Rally (3200 miles). The problem only occurred during the 2 days it took me to ride home from Shiloh on the interstates. That the problem started happening in Kentucky rather than in the Midwest this year makes me wonder if it is after all an ignition problem. But why didn't it happen in Ontario? It happens rain or shine.
The bike is a '93 R100R with 105k miles on it. Engine was replaced after seizing at about 25k. Drive shaft replaced at 85k. Transmission re-shimmed at 100k. I still have the original frame.
As far as electrical components are concerned: voltage regulator replaced at 45k, rotor replaced at 50k (open), plug wires are 7 years old, diode board preemptively replaced with Motorad Elektrik version also 7 years ago, starter replaced for the 2nd time (with ME ND starter) during the Boise RA rally in '06.
I rebuilt the carbs several years ago but they stink and occasionally leak, so it's time again and I'll do it this winter.
This week I've cleaned and lubed all electrical connections under the tank and behind the front engine cover, removed and inspected the coil with resistance values in specification and no obvious cracks or arcing, and I cleaned the petcock screens (which weren't that bad, although the red paint is starting to flake off the interior of my tank). I haven't had time to run it since and don't expect the problem to re-exhibit itself anyway until my next long trip.
I'm considering just biting the bullet and replacing the coil, ignition module and Hall Effect sensor, but the expense makes me shudder almost as bad as the bike when it's straining to hold speed. Your diagnostic thoughts and suggestions are sincerely appreciated.