The Hunting / Stalling & Surging Problem

Most BMW F650s have faced this problem during their lifetimes. It is particularly acute in the earlier single spark models (Pre 2003). Several fixes are known to cure the problem, though some machines (including mine) seem not to respond to anything. YMMV.

List of known solutions (easy to hard):
1. Run regular gas. DO NOT RUN PREMIUM.
2. Change to an extended tip spark plug. NGK iridium tipped plugs (NGKDR8EI9 or something like that). $3-5
3. Replace your air filter with a brand new one. $22-25
4. Check the rubber intake manifold (sits between the throttle body and engine head) for cracks
5. Change the plug cap aka ignition coil. $85
6. Install a fuel nanny. This topic is almost as controversial as which oil to use. Some have had good luck with Techlusion, some have not. I personally have run Techlusion for over a year and have had a good experience. $200-250
7. Change the fuel filter. $80-100
8. Trade up for a twin spark or a 4 cylinder bike. $$$?

The following documents my continuing struggle to hunt down the stalling problem. Let't not even get started on surging…

posted by xxaarraa on Mon Jan 28, 2008 8:21 pm

Searched and found nothing, though I am probably searching for the wrong thing. Bear with me.

My idle has been off recently. She constantly \"hunts\" while coasting on slow speeds with clutch in. RPM jumping between 1000 and 1500 and idle going up and down. While completely stopped, the idle is fine, only hunts while coasting. This is somehow related to the stalling problem I have been having. In stop and go traffic she stalls out repeatedly. At first I thought it was a cooling problem so I removed the engine spoiler and changed the coolant. Checked radiator fan and its working fine. The fact that the stalling is happening so soon into the ride (first 15-20 minutes in rush hour) in not so hot weather (75-80 degrees) leads me to think its not a heat issue.

The only idea in my head is a clogged air filter. Its pretty dusty at rush hour where I live which could have clogged up my air filter. The symptoms have also steadily gotten worse, which fits with my theory. Would a clogged air filter cause the motor to hunt?

If its not the air filter, could it be clutch cable related? The clutch has developed some free play, the first inch or two doesn't engage the clutch at all anymore.

I just want some wisdom before tearing into all the plastic. Please advice.

posted by damalden on Mon Jan 28, 2008 11:38 pm

try a new plug wire, it did wonders for Betty's manners.

In fact it was almost burnt through and the solid core was arcing someplace, surprising that she even ran at all

posted by johno on Tue Jan 29, 2008 4:30 am

I had the same problem with mine when I got it last year.
Put a new spark plug, and a new battery in it, and no more issues.
The original battery still started it, but stalled all the time if you didnt keep revs up when coming to a stop. A bit hard to do all the time.
Actually spat me off once when stalled in a corner changing down gears.

posted by xxaarraa on Wed May 21, 2008 7:47 pm
Just finished installing a brand new battery. The old battery in my bike was a 12 V 12 AH, I found a similar sized battery that is rated at 12V 9 AH.

Installed it and checked everything and fired her up and took a ride. The same problem still exists. The bike \"hunts\" with the revs going up and down when coasting to a stop. And it stalls every time I come to a stop. No problems if I keep the revs up. Exact same problem as before which made me change the battery in the first place. Interestingly, I took the old battery in to the battery shop and they put a volt meter on it and it read 11.9 V. Which is pretty good isn't it? This was after it was on a tender for a day (the tender burned out incidentally but thats another story).

I originally thought it was a cooling problem and changed the coolant. I had a low beam bulb blow out right when this all started. If its not coolant and not battery related, what is it????

1. I have a techlusion fuel nanny which I am going to uninstall tomorrow to see if that is the problem.
2. Are the signs consistent with a broken VR?
3. Is this potentially a faulty alternator?

Any ideas would be greatly appreciated. Thanks.

posted by ThumpAspen on Wed May 21, 2008 8:00 pm

Check for a vacuum leak at the manifold. I would expect that to cause problems at idle as well, though. All I can think of.

posted by HelmetHead on Thu May 22, 2008 2:38 am

One other simple thing to eliminate first - did you reset the BMS-C? If not, how long was the juice off for when you switched batteries? If you did a quick change and the juice was only off for a minute or two, it may not have reset. But, if it was off for fifteen minutes or more, that should have reset it.

It definitely sounds like an FI problem and not a clutch problem to me. I think it's worth checking the air filter and the spark-plug cap/wire like DAM says. Let us know what disconnecting the Fuel Nanny does, too.

posted by xxaarraa on Thu May 22, 2008 12:50 pm

Folks, I think its solved. Got rid of the Techlusion, changed out the plug, made sure the airbox was properly sealed and put a new air filter in. The BMS must have been reset as the battery was off the bike for over 24 hours. Not sure which of the above could have solved the problem, my money would be on the Techlusion. I rode to work today and rode around running some errands and everything seems fine. Today was a good test as it is 96 degrees outside.

My boss's favorite quote is \"there are no stupid questions, only stupid people.\" So thanks for putting up with stoopid.

posted by xxaarraa on Mon Jun 23, 2008 10:48 am

Looks like I spoke to soon. The problem is back.

I am starting a new thread since my old one is no longer available:

Background: 2003 CS. 8100 miles. Ridden in India in 80-90 degree weather. Original configuration when problem first appeared: Techlusion, Supertrapp, snorkel mod, engine spoiler, Mobil 1 15-50 full synth car oil. I have been alternating between regular fuel and premium depending on availability. Some gas stations in my neighborhood only sell premium. I have always used the correct starting procedure. No warning lights on the dash have lit up.

Problem: Bike would constantly "hunt" when slowing down or stopped and eventually stall. Would only happen after crawling for 10-15 minutes in heavy traffic. Never stalls when RPMs are up. Always started right up in the morning.

What I have done so far:
1. First I thought it was a cooling problem. So I removed the engine spoiler, changed the coolant and checked to make sure the radiator fan was working. Did not solve the problem.
2. Then I thought it was a battery problem. Changed to a brand new battery, made sure terminals were tight. Since the new battery was slightly smaller than OEM at 12V 9AH, I removed the turn signals and low-beam to reduce draw. Did not solve problem.
3. Changed the spark plug and air filter. Was already running the NGK Iridium extended tip plug and changed to a brand a new of those. Did not solve the problem.
4. Someone suggested it was the Techlusion fuel nanny. Removed it. Problem seemed to go away temporarily, but is now back.

Never stalls when the RPM is up. Only stalls after idling for 10-15 minutes and when slowing down or stopped. What's next?

posted by xxaarraa on Tue Jun 24, 2008 7:30 am


Its not the intake manifold. I tore into the bike this morning and inspected the manifold closely. It seems to be alright. Incidentally, I think I stripped one of the allen bolts holding the manifold to the head so I didn't take it off completely, but went over it in detail with a flashlight. No cracks or any signs of wear. I siphoned off all the old gas and will be filling up with fresh, ordinary gas on my way to work. I am also going to run a can of injector cleaner through the system.

I patched up the two quarter-sized holes I made in the snorkel per the snorkel mod in the FAQs. Maybe the extra air flowing in might have had a part to play.

I only have two other things in mind:
1. Spark plug cap/wire
2. Fuel filter
Unfortunately, neither of the above is cheap.

Could this be oil related? I am running Mobil 1 15-50 synthetic car oil. Could that have anything to do with it?

Any thoughts?

The saga continues. Since the last update, I have:

  • Replaced the ignition coil,
  • Replaced fuel filter
  • Replaced clutch cable
  • Repacked my Supertrapp exhaust with new fiberglass packing
  • Soaked the fuel injector overnight in injector cleaner
  • Added injector cleaner to a tank of new fuel
  • Removed charcoal canister

And Nada, no effect. Still stalls and cuts out. JetDoc suggested to plug the O2 sensor back in. I had unplugged and taped it over a year ago when installing the Techlusion and will plug it back in and see what it does.

Plugged the O2 sensor back in but still no go. Same symptoms, zero improvement. Yellowmc at BBG mentioned he is having the same problems and is taking his bike to the dealer to get checked out. Here's waiting fingers crossed for them to figure out what the heck is wrong.

Meaning to post this for a while. I solved (temporarily?) the stalling problem by adjusting the idle. I now idle it at 1600 or so and just did it by fiddling with the throttle cable near the throttle. This has solved my stalling problem. I wonder whether the constant rush hour commute had weakened the throttle cable causing more slack? I have to put in a new throttle cable and check, but for now, she runs!

From ChaplainSparky: 6/30/2009

Last Fall, Oct '08, I took my 05 CS in for a 30K service. It was having problems with poor performance. Would not accelerate unless a very light hand was on the throttle. The shop reported that the exhaust manifold would glow red after about 2.5 minutes at idle. They hunted for a few hours and could not find the problem.

Took the bike back and this spring proceeded to troubleshoot the problem on my own.
I started at the gas tank and moved forward through the intake system and exhaust looking/check for leaks.

What I replaced was: the o rings in the throttle body and intake stub/manifold. The red hot exhaust went away. The poor performance still continued. and I finally replaced the exhaust manifold gasket. What I found pulling the old one surprised me. Seems that the dealer did not install the last one properly. The exhaust manifold failed under warranty and it was replaced along with the o2 sensor. I have ordered some new iridium plugs to complete the repair, hopefully.

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