Bike:1977 r100/7 43K Kms (no bean can, no electrics, mechanical advance) Bike starts well with choke, idles at 900 After 2-3 km warm up, choke off, idles about 1100 After 20-30 minutes of aggressive throttle, idle "sticks" at 2500-3000 If I drag the rear brake to less than 2500 rpm, bike returns to normal 1100 idle If I turn off the key and restart, bike returns to normal idle Carbs have been rebuilt (all gaskets/o-rings/jets/needles/floats etc.). Mix, idle and balance set by 55-year-old, factory-trained bmw tech. Timing: seems good, but not personally verified by me, but the engine and bike are smooth and robust, no flat or dead spots in the rev range. Valves: good, properly adjusted including valve lash. Heads: retorqued and pushrod seals re-sealed Cables: in good repair Intake gaskets: no leaks per test with wd40, gaskets fresh in the last two years. Mechanical advance: carb cleaner, varsol dunk, silicone lube - seems ok, though "up-down" sloppy? But I have nothing to compare against. So, why does the bike idle high after 30 minutes of riding, but not after 10 minutes? Given I can drag the brake, force down the rpm mechanically and then it idles correctly or just turn off the key and restart and it idles correctly, that would seem to indicate a stuck advance mechanism. But, given I just cleaned and lubed the hell out of it, that seems like it can't be the problem. I have googled "site:www.advrider.com high idle r100" and read for the last two hours. I have read Snowbum's stuff. (Clearly brilliant, but he needs a good editor and to stop using bracketed after thoughts. As you will note, they ruin whatever flow may have been generated.) I am now more confused after the long discussions of jets, needles, choke gaskets (though they are actually an enricher circuit) 323 jets, in is richer, turn mixture out, too rich, too lean, leaking vaccuum, etc. What I know is I can't recreate the symptoms in the garage. High idle sticking only happens after 20-30 minutes of spirited riding. Bike pulls and runs great, pre and post high idle sticking. I can't tell it is going to do it until it does it, but it does it every time after the bike has been run hard. Please help, and if it isn't overly annoying, perhaps a step-by-step process to diagnosis and repair. I'm in Canada. The weather is still dodgy (-15C this morn, snow yesterday, +4C now). I promise to report back precise findings as I am able. I have a full rack of wrenches, feeler gauges, a timing light and a multimeter. I was raised on a ranch and I can fix stuff, but I am not an airhead or any other kind of guru. Just an eager, cheap, middle-aged guy that wants his airhead to return his affection.