Engine nearly cuts out whilst accelerating (F650 GS Dakar Dual Spark)

[Bjorn]

Hi,

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?

Cheers
Bjorn

[henryuk]

does it happen under throttle without load (i.e. revving with clutch in) or just under load?

[docsherlock]

definitely could be fuel pump
get them to test the flow rate

[Bjorn]

Originally Posted by henryuk

does it happen under throttle without load (i.e. revving with clutch in) or just under load?

Happens without and without load

[TurboCharger]

Hi Bjorn,

I agree with Docsherlock.

Given that you have cleaned the fuel injection then I would get swap out the fuel pump with another bike if possible and see if this fixes the problem. If you can't do this then try as Docsherlock suggested a flow rate test.

Obviously if the problem occurs during with an without load then it *should* make it easier to find the problem.

Regarding poor fuel quality, Miquel Silvestre while in Egypt had a lot of bad fuel, possibly dirty and possibly with water but definitely with high alcohol (ethanol) content. His experience was a little like running out of fuel or loosing power as you describe. So I would also try to get some better quality fuel if this is at all possible in Columbia.

Good luck and let us know how it goes.

Cheers,

Pascal & Arja

[Bjorn]

Hej Pascal & Arja!

Still in Norway? Hope you got heated vests

The Ruta40 guys have 2 other GS in their shop (second hand), so maybe they let me swap a few things to make the diagnosis easier. I'll try the fuel pump first – then look into the air/throttle body sensors...

Better quality fuel in Colombia isn't possible. I always go for the high octane one. But maybe the lower octane one would be easier (it may have LESS alcohol, who knows?)

[Bjorn]

OK – Went back to the beemer shop here. We tested everything and it turned out to be one of the coils (the bit above the spark-plugs). We put one from a GS1200 on – looks very much the same as the F650 twin spark's. (BMW part number is different, but the manufacturer's number is identical).

This took care of a large part of the problem, but whenever I pull the throttle REAL quickly, the engine still cuts out from time to time. Guess this could be down to the bad fuel though.

[TurboCharger]

Hey Bjorn,

We're actually now in Switzerland, we have been working to get some more $$$ for the next trip. Arja is learning French and German, and I'm learning Spanish (for South America). We're going to do a tour around the Mediterranean Sea later in the year so hopefully Egypt will be calm by then.

Glad to hear that the coil mostly fixed the problem. So I guess you'll be only using the accelertor lightly, this could be quite dangerous especially if you want to get away quickly and then the engine dies.

It will be interesting to hear if the problem goes away with different fuel.

Good luck and safe travels!

Cheers,

Pascal & Arja