I'm on a longer trip, currently in Colombia. Since about 1000 km I've got the problem that the engine nearly cuts out/stalls when accelerating. First the problem only occured during startup:
Engine on, 1st gear, a bit of throttle/release clutch -> front suspension slightly dives in. Only by pulling the clutch I could avoid the engine cutting off. On 2nd attempt, things were fine most of the time. Same for when I had a 20-30 min break (warm engine): no problems.
Luckily, I was close to one of the FINEST beemer shops in South America: Ruta40 in Medellin/Colombia. The guys are SUPER friendly and helpful. I could even do some work myself in their workshop to save costs.
The head mechanic (Felipe) listened to the engine & said the valves are all good, no need to even look at them.
Other than that:
Engine: 120000 km
Oil change: 1500 km ago (20W50 Semisynthetic Castrol)
Fuel Filter: 5000km
Battery: 5000km, and just serviced/recharged yesterday
Spark Plugs: Iridium, about 10000km
Air Filter: just cleaned
Fuel Injection & throttle body: cleaned via ultrasound (Ruta40... US$15
Once I had the bike back together, we connected it to the BMW diagnostic tool. All good.
So I took the bike from BMW back to the hostel (3km city traffic). And that's when the problem reoccured. But this time ALL THE WAY, i.e. with warm engine.
Every time I had to wait / idle the engine for a few seconds (traffic lights, filtering, etc...) the engine nearly cut out most of the times. The exhaust then sounded as if someone was holding their hand behind the exhaust, kind of a "puffing" or misfiring sound, and hardly any power.
And when I accelerated a bit more (say from 20 km/h to 40-50), the full acceleration/power came with a 1-2 second delay (sometimes, not always). Lots of playing around with throtle & clutch – not really a fun ride back to the hostel.
Accodring to BMW, everything's OK. Anyone here got any ideas? I'd like to think that it can't be the spark plugs, as idling is OK and the bike starts up OK.
The petrol here in Colombia has a fair amount of alcohol, but the guys at Ruta40 said that is usually not a problem. And after all, the fuel in Bolivia is a lot worse (and I didn't have a problem there).
Maybe the fuel pump? Can a fuel pump be "temperamental" or is it more a "it works or it doesn't work at all" kind of scenario?
The last time I had leaded petrol is about 40000km ago I guess, back in Turkmenistan for about 1000km. According to a trustworthy BMW mechanic, the catalysator should be OK with this.
Anyone here had similar problems in the past?