It started as a 'dead spot' at around 4500rpm in top gear which felt like the ignition had turned off, but when you throttled down a bit it'd pick up again.

Slowly over the following two days it got worse with the 'dead spot' growing down the rev range until it died completely 70km south of Antofagasta. It was almost as if the 'Hand of the Desert' statue was a stop sign.

Thanks to some friendly truckers we make it into town before sundown (bleeding cold in the desert) & I've been trying to figure out whats broken.

The ignition lead was a bit chewed up from rubbing on something so I´ve already swapped that out (and the plug), but the problem is still there.

If anyone has any ideas on the cause, PLEASE let me know, its driving me nuts!

Symptoms are :-
- Can start the engine with a little perseverence
- Engine WILL idle
- Opening the throttle (even a little) causes the engine to run rough & stumble to a halt.
- Has a healthy spark
- Removing the airbox & turning the engine over (full throttle with the plug disconnected) shows that the injector is injecting nicely.
- Can see the engine backfiring (flash in the intake manifold) when opening the throttle a little by peering down the throttle stub.

I'm starting to suspect either a burnt intake valve or a screwed airflow sensor on the throttle stub..... but if anyone has seen this before please let me know.

Cheers,

Bob

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It sounds like it is running lean...not getting enough fuel just off idle. Plus you say it is backfiring.

"Injecting nicely"? What is nicely? But are you getting the right amount of fuel? I'm not familiar with that model (I have a GS Adventure), but is the throttle potentiometer (throttle position) working? What voltages are you getting?

If you can do a simple leak-down or compression test, that'll eliminate valves, etc.

Just an educated guess.

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- If motorcyclists claim to be individuals, why then do so many of them ride in packs?

Thanks for the pointers. The valves are my main suspect as the engine was running lean for quite a while thanks to a split inlet manifold, long enough to do some damage I think.

Checking the throttle position sensor was something I hadnt though of, anyone know what voltages/resistances it should be at as thats easy enough to check.

We've kinda fallen on our feet (for once) as the truck company that rescued us from the side of the road have arranged for us to be stowaways on another truck heading north, which is very nice of them.

With luck we'll be in range of the border with Peru in a day or two, then its back to Arequipa (via pickup truck) to a nice workshop with lots of tools.

Or at least, thats the plan......

Bob y Angie

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Sorry, I don't have a clue. I'm new to fuel infected motorcycles.

Try the Chain Gang
http://f650.com/website

http://faq.f650.com/GSFAQs/FuelInjectionFAQ.htm

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- If motorcyclists claim to be individuals, why then do so many of them ride in packs?

I think you can forget about the valves causing the problem described by you. I remember a partially burned exhaust valve on one of my KLR 650C a few years ago. Exhaust valves are the ones who suffer due to overheating when clearance is set too tight or the engine runs very lean. A typical and unmistakable sign of a bad exhaust valve is that it influences the idling of the engine means the engine will idle at higher rpm when it heats up. Careful! This might be disguised or countersteered by the electronic motor management of the F650GS.
Within 20 years in the motorcycle trade I have only seen two types of damage on inlet valves: 1. Bent valve caused by violently overreving the engine or snapped / jumped timing chain. This damage obviously does not develop over time and the engine (usually) does not run any more. 2. Besides that wear on inlet valves does occur but I have NEVER seen an inlet valve that failed from wear or caused noticable problems except 1. of course.
The engine running too lean will always burn an exhaust valve as the thermical strain is a lot higher than on the intake valve. As mentioned the first noticable symptom of a valve problem is change of idling speed with heating up of the engine. Starting problems do usually not occur on modern 4stroke singles as the automatic decompressors and powerful electric starters disguise "slightly low compression" start problems. As the problem gets worse the bike will eventually lose power and get difficult to start. It will never develop a "dead spot".

The backfiring points straight at an ignition or fuel problem. Ignition problems on CDI or TCI ignition systems (used on most bikes that don't have contacts) are extremely rare and manifest themselves usually by having no spark at all. Sometimes you get temperature related problems caused by bad contacts on ignition circuitboards. Although I don't know how the ignition of the BMW EMM works I don't think it's the cause of your troubles.

My main suspect is a sensor input problem on the EMM: If the computer receives incomplete information from the sensors (airflow / temperature / throttle position, lambda...) it is programmed to go into an emergency mode to keep the vehicle going or / and to prevent engine damage. Let's say throttle sensor bust: The engine will eventually start as the computer asumes the butterfly valve closed and act accordingly. The engine might run perfectly in certain throttle positions as the throttle sensor is a variable resistor and prone to partial malfunction through mechanical damage, water or dirt. To check you can simply check the resistance of the sensor with an electronic tester while operating the throttle slowly. The resistance will typically vary from zero to 5 or 20KOhm smoothly.
I had a similar problem with very similar symptoms on a very different bike (GPZ 1100 DFI) ages ago. A new throttle sensor sorted it out relatively cheaply.

Good luck!

Wow, what can I say....many thanks for taking the time to post such an informative reply.

I'm *still* hunting around Arequipa for a pressure regulator so I can do a leak down test on the valves...a multimeter is a lot easier to find.

Thanks again.

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Well, whatevers causing the problem its not the throttle position sensor. It registers between 0 & 5k ohm resistance & moves smoothly across the range. Nuts, its never anything simple.

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Ok the other sensors are

Engine temperature - the resistance of this changes with temperature (duh) ... it may have gone open circuit and be causing too much fuel to flow .. this usually stops the motor dead...

Air temperature - same as the engine temperature .. but with less effect on teh amount of fuel injected.

The temperature sensors would be aorung the 2k ohm mark at around 20 C IIRC. They should be fairly close in readings with teh engine 'cold' ie both at the same temperature.

Umm What else CO2 sensor (lamba sensor) would be screwed into the exhaust somewheres before the muffler. Would give a small voltage reading around ummm memory .. umm errr think it would ba around 0.2 volts but I'm probably wrong...

Oh the fuel pressure ... sometimes the regulator gets blocked and you don't get fuel returning to the fuel tank. And you'll have a fuel filter in there - may also be blocked .. try blowing throught it when it is off the bike..

Enough.

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Regards Frank Warner
motorcycles BMW R80 G/S 1981, BMW K11LT 1993, BMW K75 G/S

Thanks Frank,

Well here's the latest. Its not fuel pressure, have oodles of that as it fired a slug of gas further than expected the garage when I unhooked a hose. Its got quite a range, the neighbours dog didnt appreciate it much.

I changed out the filter/regulator as I had a spare & its not that. I also changed out the fuel injector, no change.

Still cant find a bloody pressure regulator to check the valves so the head will have to come off tomorrow, get stripped down & seats checked with engineers blue.

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What happened to this one? Bike burned out and claimed from insurance?

Naaah.....that'd be giving up too easily, and besides, what insurance ?

The bike is in peices, lots & lots of peices. I decided to strip it down & check everything very thoroughly. Removing the cylinder head revealed lots of carbonised crud in the engine so its an over-fuelling problem but the valves were OK. There was corrosion in the wiring (thanks to Salar Uyuni no doubt) and lots of other minor things.

Thanks to BMW Battersea I have a box of parts on the way to Peru (contact is Ben Nagel). They've been extremely helpful so I opted to change out everything thats either busted, past its 'please put in the bin' date or showing signs of wear.

Lamda sensor, piston rings, ignition coil, ignition lead (looked like a rat had nibbled it), air temp sensor, upper & lower fork bushes, the list goes on......

Apart from the souvenier scratches & dent collection it'll be like a new bike when I've finished....and ready to head for Alaska when it warms up a bit.

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It was either the ignition cable, CDI unit, oxygen sensor or some corrosion in the wiring.

I changed out all three parts during a bloody good service & everything works now. I'm the happiest happy person in Peru.

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