KTM 125 duke stalling

[gavcol]

Hi, I have a ktm duke 125 that I bought a few weeks ago. I picked the bike up with a known fault of not being able to engage any gear. I knew that it would probably need an engine strip down. Long story short, some of the piston had broken and a fragment was stuck in the gears. Cleared it all out and replaced the piston.

This is my first engine strip down so I wasn't expecting it to go plain sailing on the first attempt. I have been following a workshop manual that I have. When re-installing the engine there is one connector that I can not find a home for, it's under the air box (close to the throttle body), has 2 wires and is tie wrapped with a range of about 5cm. I've searched for it's home for so long and have decided that it doesn't have one.

Bike fully assembled and it dies after about 60 seconds (sometimes a little less). I can drive the bike through 1st, second and third but then it just dies.
The bike will start first time after ignition is switched on, leave it and the rpms gradually fall before it cuts out after about 60 secs. Ignition off and on a few times and will start again first time. If I just try to restart it wont start.

I've checked the fuel pump by taking the hose off and letting it flow in to a container whilst holding the start button, that looks good and when the bike is running I can hear the pump working in the fuel tank.

I've had the injector off and forced some carb cleaner through it, only 2 of the jets are working (out of 4) so will order a new one of those but I don't think that is the cause of the fault.

I can't keep it running long enough to read the fault codes off it.
It has a lovely clean piston, clean cylinder head and a brand new spark plug. Battery is fully charged.
Does anyone have any ideas? Anything that I can check?

[jaffa90]

I know nowt about your bike (old hat), did you find out why " some of the piston had broken and a fragment was stuck in the gears."?

Also 4 jets are better than 2 (more fuel).

Fuel pumps should be pressure tested with a breathing tank.

Also i will pass on that connector because fuel injected bikes have many.

Also how do you drive a bike.

[A100man]

Does your manual have a wiring diagram that shows the currently disconnected part? Without knowing what it is you/we cannot discount its importance.
____________________
Now: A100, GT250A, XJ598, FZ750

Then: Fizz, RS200, KL250, XJ550, Laverda Alpina, XJ600, FZS600

[Andy Perrett]

As above, the 2 wire connector right by the throttle body, under the airbox, sounds a bit like it's for a sensor, such as a MAF, to determine fuelling.

I think you need to at least get the wire colours and have a look for 2 wires that colour next to each other, on the wiring diagram.

[gavcol]

Have done so much for this over the past few days and i'm not getting anywhere.
Firstly the connector is dirtier than the other connectors that I have taken off the throttle body to check.
My throttle body has TMAP (Temp and air pressure) sensor, fuel injector, throttle position sensor and idle controller. These are the only plugs on the throttle body and they are all connected.
One of the wires goes back to the ecu pin 15, I have the 2012 workshop manual and I believe it is the same bike as the 2015. All of the ECU cables from the diagrams are present there is one extra cable in the ecu connector and it's pin 15. So i'm 95% certain this cable is for a different bike (maybe the 390 shares the same harness).
Work that i've done over the past 2 days;
Changed the Head gasket as didn't have a new one when put the engine back together, checked the timing marks line up.
removed fuel pump and cleaned pump bag. I'm pretty sure that i can hear the fuel flowing back into the tank through the return valve so it must be at the right pressure (unless that valve has broken). Injectors have been blown out from both ends and I get a really good mist out of them now up
Spark plug is brand new and has white powder on it so tried the old one.
Checked the cylinder ground wire
Ran it with no oil and no coolant (to rule out a leak). Only the once for 60 secs till it died.
All the times i'm running it is without the air filter box connected.
A bit more depth on the symptom - Start's first time fine, increase throttle to about 3k rpm, after 4 or 5 secs the revs gradually start to fall, increase throttle to maintain 3k rpm, again after 4 or 5 secs rpm starts to full, over half throttle trying to maintain 3k rpm. At this point the exhaust gasses start clouding white. The density of the smoke increases, I can hear a sucking noise from the engine and then it dies.
After all of the checks I made above the symptoms are the same.
I tried running without the TMAP sensor connected and I get same symptoms but with a flashing ecu light

[Andy Perrett]

60 seconds without oil? Rather you than me. What were you trying to prove here?

At this stage, maybe a compression/leak down test might be the best step forward? Cheap compression testers are not too much money.

You definitely don't have a head leak then? No water in oil or vice versa?
The white smoke and sucking noise sounds like water jacket leak.

[gavcol]

I think that I have a compression tester somewhere, will dig it out.
White smoke + white residue on the spark plug, was wondering if once it heats up slightly perhaps some oil was getting through.
I noticed just now that when it stalls, I switch ignition off and then on again, fuel pump doesn't come on. Turn the ignition off and then on again and it comes on. If I apply 12 v to the pump it runs continuously. Is the pump designed to run continuously or does the ecu control it and if so how? I haven't seen a fuel pressure sensor anywhere in the manual so i'm guessing that it runs constantly and any over pressure is released back into the tank through the return valve

[gavcol]

UPDATE - £120 on a used fuel pump assembly. Same fault so it's nothing in the fuel tank

[Andy Perrett]

Post a video of the white smoke or the plug with the white still on it.

A very lean fuelled plug can almost go white, but let's not forget that oil and water makes a white emulsion too.

If you take the oil filler cap off, any signs of white sludge in there? Does the oil look clean? Is it losing coolant, even a little?

[gavcol]

I just went out and took a video. I pushed past the smokey stage and this time it didn't stall.
The smoke cleared up and it seemed to settle down. I may be misjudging the new fuel pump. I'll re-assemble and take it for a drive, will let you know how it goes

[Mysteriass]

Now it'll have the same problem but with a different cause.

"Err, it only lasted 60 seconds and got slower and slower the more I tried to rev it"

So might be worth remembering to put oil in before going out.

[Andy Perrett]

[gavcol]

Nope. Put it all back together and took it for a ride today. Didn't get very far. I ran it with no oil for 60 secs at most. I don't think that'll cause any problems.
Plan now is to compression test at the weekend. I think the white smoke is a red herring. It didn't push anything out on the ride. Injector or ECU maybe? Not firing the fuel at the right time?

[Andy Perrett]

[gavcol]

Yeah, there's no cross contamination. Hard to say on the level's I've had to drain and refill so much.

[Andy Perrett]

[Mysteriass]

There's usually an arrow on top of the piston that indicates that you must face that arrow towards the exhaust port.

Once you've put the piston in the right way there's a very specific order that the rings are arranged. Each ring also has a very specific orientation.

Not only that but some rings expect to be put in the right way up (They're usually stamped with a symbol to indicate the top).

I'm wondering if there's been a ballsup here somewhere?

Those rings in wrong might cause running problems and smoke. If the piston is in the wrong way - and consequently the rings arsebackwards also - there'll not only be smoke but a hole in your wallet.

[gavcol]

I didn't know that piston rings had an orientation. I replaced the piston with a used one so just replaced the old one with the arrow facing the same way as the one I removed and left the piston rings as they were. Would the piston ring issue show up when I compression test?

[Andy Perrett]

Why fit a second hand piston? The old one blew up.

A new one can’t be over £40 for a 125 4T

[Islander]

[gavcol]

Ok, looks like I'm taking the engine off again. I'll get a new set of rings and replace them. The reason I bought the piston second hand is that to buy it new it's 170

[Andy Perrett]

[gavcol]

UPDATE - No progress made!
All of the following parts have been replaced in the last week with used parts.
Lambada Sensor and Front exhaust
Throttle Body with TMAP sensor, throttle position sensor, injector and idle controller.
Ignition coil.
I got my compression tester but it doesn't fit so ordering a new one.
Exactly the same system.

[Robby]

If it runs for 60 seconds and then gradually dies, I would be expected a fuel pressure problem.

For diagnosis only, try running it with a temporary direct 12v feed to the fuel pump. If it keeps running past the usual point, then something is telling the fuel pump to stop after about a minute.

Also make sure the battery on the bike is fully charged before trying anything. Running out of electricity feels a lot like running out of fuel, and you might have trashed the alternator with bits of piston.

[gavcol]

I was thinking battery yesterday, hadn't done anything with it yet as starting fine and comes up with low battery when it's low.
Will try switching in a car battery and wiring the fuel pump direct.