Odd. Very odd.

**Ixion** · 22nd February 2009, 20:46

A strange thing happened.

I was wobbling down to Paeroa on the bMW. Along the Miranda Road. Everything all running good. And I went over one of those little bridges they have, that had a drop off at the end, as they do, and came down fairly hard off it. No great speed cos I am very slow and never speed, just the speed that one does on that road, certainly not much more than 80mph.

Almost immediately I landed (within 2 or 3 seconds), I lost power. The loss quickly got worse, and the engine was barely running.

Spluttering , backfiring (exhaust and inlet). Dropped into first gear and was just able to keep headway on, heading for a farm gate about half a kilometre up the road. Engine would die "durrggggghhhh", splutter, cough, misfire, then pick up and rev fully for a few seconds (all this on full throttle). The bursts of revviness enabled me to creep along at maybe 10kph, kangaroo hopping like mad . Sometimes it would fall away and threaten to stall, but if I pulled in the clutch it would do the durrgghh, splutter, backfire, rev thing .

While this was happening I could hear a noise, not very loud , a bit like the chattering of a demented squirrel that's been on P for a week.

Just as I was nearing the farm gate, and preparing for the worst, I pulled in the clutch for another hop, when it spluutered, coughed, back fired ,revved and kept revving! Clean and free. Hallelujah.

And after that it was fine. Didn't miss a beat the rest of the way there, or back. Started no problem at Ngatea and Paeroa.

What could have caused that d'y think? Certainly I think it was fuelling (all electrics were fine)

Did the negative G over the bump send all the fuel (about 1/4 full) to the top of the tank, causing an airlock in the fuel pump? Seems rather, um, improbable.

Did the bump jolt loose a fuel pump connection, which magically jolted on again? Unlikely.

Did the bump shake loose some sort of fuel tank splooge that finally went away ?

Wasn't water in the fuel, bike was running absolutely fine down from Dorkland, and fine afterward.

Never done anything like it before. Looked the machine over at Ngatea, but couldn't see anything amiss (peered in the fuel tank too)

It's fuel injected. It's shaken my simple faith in FI.

**McDuck** · 22nd February 2009, 20:51

Originally Posted by Ixion

A strange thing happened.

I was wobbling down to Paeroa on the bMW. Along the Miranda Road. Everything all running good. And I went over one of those little bridges they have, that had a drop off at the end, as they do, and came down fairly hard off it. No great speed cos I am very slow and never speed, just the speed that one does on that road, certainly not much more than 80mph.

Almost immediately I landed (within 2 or 3 seconds), I lost power. The loss quickly got worse, and the engine was barely running.

Spluttering , backfiring (exhaust and inlet). Dropped into first gear and was just able to keep headway on, heading for a farm gate about half a kilometre up the road. Engine would die "durrggggghhhh", splutter, cough, misfire, then pick up and rev fully for a few seconds (all this on full throttle). The bursts of revviness enabled me to creep along at maybe 10kph, kangaroo hopping like mad . Sometimes it would fall away and threaten to stall, but if I pulled in the clutch it would do the durrgghh, splutter, backfire, rev thing .

While this was happening I could hear a noise, not very loud , a bit like the chattering of a demented squirrel that's been on P for a week.

Just as I was nearing the farm gate, and preparing for the worst, I pulled in the clutch for another hop, when it spluutered, coughed, back fired ,revved and kept revving! Clean and free. Hallelujah.

And after that it was fine. Didn't miss a beat the rest of the way there, or back. Started no problem at Ngatea and Paeroa.

What could have caused that d'y think? Certainly I think it was fuelling (all electrics were fine)

Did the negative G over the bump send all the fuel (about 1/4 full) to the top of the tank, causing an airlock in the fuel pump? Seems rather, um, improbable.

Did the bump jolt loose a fuel pump connection, which magically jolted on again? Unlikely.

Did the bump shake loose some sort of fuel tank splooge that finally went away ?

Wasn't water in the fuel, bike was running absolutely fine down from Dorkland, and fine afterward.

Never done anything like it before. Looked the machine over at Ngatea, but couldn't see anything amiss (peered in the fuel tank too)

It's fuel injected. It's shaken my simple faith in FI.

It could be water, if the inlet is above the tank bottom the fuel would sit on the water. When it went over the bump it flicked the hole lot up and the inlet sucked in a little water?

**3umph** · 22nd February 2009, 20:59

Originally Posted by Ixion

A strange thing happened.

I was wobbling down to Paeroa on the bMW. Along the Miranda Road. Everything all running good. And I went over one of those little bridges they have, that had a drop off at the end, as they do, and came down fairly hard off it. No great speed cos I am very slow and never speed, just the speed that one does on that road, certainly not much more than 80mph.

Almost immediately I landed (within 2 or 3 seconds), I lost power. The loss quickly got worse, and the engine was barely running.

Spluttering , backfiring (exhaust and inlet). Dropped into first gear and was just able to keep headway on, heading for a farm gate about half a kilometre up the road. Engine would die "durrggggghhhh", splutter, cough, misfire, then pick up and rev fully for a few seconds (all this on full throttle). The bursts of revviness enabled me to creep along at maybe 10kph, kangaroo hopping like mad . Sometimes it would fall away and threaten to stall, but if I pulled in the clutch it would do the durrgghh, splutter, backfire, rev thing .

While this was happening I could hear a noise, not very loud , a bit like the chattering of a demented squirrel that's been on P for a week.

Just as I was nearing the farm gate, and preparing for the worst, I pulled in the clutch for another hop, when it spluutered, coughed, back fired ,revved and kept revving! Clean and free. Hallelujah.

And after that it was fine. Didn't miss a beat the rest of the way there, or back. Started no problem at Ngatea and Paeroa.

What could have caused that d'y think? Certainly I think it was fuelling (all electrics were fine)

Did the negative G over the bump send all the fuel (about 1/4 full) to the top of the tank, causing an airlock in the fuel pump? Seems rather, um, improbable.

Did the bump jolt loose a fuel pump connection, which magically jolted on again? Unlikely.

Did the bump shake loose some sort of fuel tank splooge that finally went away ?

Wasn't water in the fuel, bike was running absolutely fine down from Dorkland, and fine afterward.

Never done anything like it before. Looked the machine over at Ngatea, but couldn't see anything amiss (peered in the fuel tank too)

It's fuel injected. It's shaken my simple faith in FI.

Could it of been the stand partly down??? don't know your bike but if it has a cut off switch on the stand when in gear this could of been on the brink of flicking on and off but as you slowed it went back into place and took off like normal...

just an idea

**Ixion** · 22nd February 2009, 21:02

Originally Posted by 3umph

Could it of been the stand partly down??? don't know your bike but if it has a cut off switch on the stand when in gear this could of been on the brink of flicking on and off but as you slowed it went back into place and took off like normal...

just an idea

No stand cut off. No safety type switches at all.

**smoky** · 22nd February 2009, 21:05

I had a V twin 800 - the same thing happened as you described, checked everything, found nothing
It happened again and I tried to crawl along home as you described - occasionally it would run OK and I'd make some distance - I should of stopped riding it;
Turns out it was an exhaust flange leak where it bolts onto the motor. trying to keep riding it resulted in a burnt valve?
I know it sounds strange and unrelated, but actually when you think it thru; it was upsetting the fuel scavenging dynamics of one of the cylinders and thus running too lean, also upsetting the balance between the two carbs and messing with the fuel supply to the second cylinder.
It's a long shot but check your exhaust.

I had a similar thing on another bike, and it turned out to be the gradual breakdown of the CDI unit.

**Ixion** · 22nd February 2009, 21:26

FI not carbs. And such a dereliction would (a) not be likely to start instantly and (b) be even less likely to completly cure itself instantly.

It went from running absolutely fine, to durgggh spluuter cough rev durrgh etc in a couple of seconds. And when it cleared it went from durggh etc to running absolutely fine within a second

I suspect (without evidence) that the squirrel chattering was the fuel pump (inside the tank), sucking air. I think it progressively went from three cylinders to two to one to none, then randomly played the combinations of 0 1 2 and 3 . The moments when 3 were running being the revvy moments. Then all three climbed back aboard and all was well.

I can think of lots of reasons for such a problem. I can think of far fewer that will completly cure themselves after a few seconds , and which are precipitated by a bad bump (though the bump may be coincidental of course) .

**Madness** · 22nd February 2009, 21:29

http://www.kiwibiker.co.nz/forums/sh...ad.php?t=93075

**McDuck** · 22nd February 2009, 21:34

My next guess is there is a sencer having a sulk which it got over after a min or two...

**Motu** · 22nd February 2009, 21:39

Do they have a swirl pot? Where the returning fuel is fed to keep the level on the suction side of the pump high.Having the swirl pot depleted of fuel would cause starvation,until it returned to a normal level,and then running perfectly again.To cause this sort of fuel starvation you would need some sort of air leak at the suction side of the pump.

What sort of air flow meter do they use? Check the intake boot.

**TLDV8** · 22nd February 2009, 21:42

Sounds like cavitation of the shuttlecock then the pump hyperventilated.

**smoky** · 22nd February 2009, 21:51

Originally Posted by TLDV8

Sounds like cavitation of the shuttlecock then the pump hyperventilated.

Or hyperventilation pump of your cock while cavitating the shuttle

**Ixion** · 22nd February 2009, 22:03

No swirl pot. The airflow meter is a vane type, same as BMW cars.

One possibility is that BMW have a trick to save fuel. If the computer detects that the throttle position sensor switch shows a fully closed throttle, but revs are greater than 2500 (ie, you are on the overrun) , it cuts off the fuel . The bump could have deranged the TPS switch temporarily causing the computer to shut off the fuel whenever the revs exceeded 2500. Maybe. Perhaps. Or not. Too much black magic here. Maybe I might resign from SAMAC (the Society for the Abolition of that Monstrous Abomination the Carburettor. )

It wasn't a very big bump , though.

**Motu** · 22nd February 2009, 22:40

The vane type is a mechanical device,unlike the later more esoteric hocus pocus stuff.They give a bit of trouble in cars,although given how many and how old,failures wouldn't blip any Bosch radar.A motorcycle is a much harsher enviroment....but you should have your finger on the pulse of K75 air flow meter problems.

False air.....or false fuel.It wasn't monitoring one or the other - but thought it was.

**Ixion** · 22nd February 2009, 22:53

There's a bit of history of the AFM needing adjustment , to eliminate black smoke. But i've not encountered any report of complete failure.

A third suspect is fuel flow somehow. Let the electronic whizzies think what they may, if there is no fuel , or the pump won't pump it, strange things will happen. . The whizzies calculate how long and when to open the injectors. But they blithely assume that there will be petrol in the line to inject.

The deranged squirrel rattle sounded very like a pump cavitating. No, I don't know why it would do that. The initial effect was exactly like running out of fuel on an FI engine - in fact for a moment I thought I had.

**McDuck** · 23rd February 2009, 06:38

Originally Posted by Ixion

There's a bit of history of the AFM needing adjustment , to eliminate black smoke. But i've not encountered any report of complete failure.

A third suspect is fuel flow somehow. Let the electronic whizzies think what they may, if there is no fuel , or the pump won't pump it, strange things will happen. . The whizzies calculate how long and when to open the injectors. But they blithely assume that there will be petrol in the line to inject.

The deranged squirrel rattle sounded very like a pump cavitating. No, I don't know why it would do that. The initial effect was exactly like running out of fuel on an FI engine - in fact for a moment I thought I had.

Maby go back to the spot and see if you can do it again....