Hey guys, I think I'm back, fell off the edge of the map for a while there. Sorry.
So my Duke is now on its third major failure, first was a BHG, then my flywheel sheared its bolts and destroyed the stator side of the motor.
Bought a lower mileage motor from eBay and it failed three months later, not sure what's wrong there, but I was a bit over it TBH, hence me disappearing for a while.
Ready to get it fixed again, after my neighbour that builds hotrods as a passtime kindly offered to help the other day.
Long story short, it wasn't the 390 motor's fault, but rather the mods I had. Specifically in my case both the original and replacement motors failed after the open airbox lid.
Not due to it though, rather due to incorrect fuelling, so not adjusting for the lid after fitment. Took me two failures to realise. Go figure.
Good to have you back, Johann! I'm sure I'm not the only one here who wondered what had become of you.... I'm relieved to hear it was only blown motors and not something worse that was keeping you away. You are now officially a grizzled veteran who has been through the engine wars - authorized to dispense wisdom based on real, unintended and regrettable experience.
And I think you have made my case for leaving my Duke's engine virginally intact: no mods to intake or exhaust, no fuel controller.
Cheers Phil, if you want to do engine mods, IMHO do the factory K&N, Akrapovic slip-on and Akrapovic fuel map. I was offered a demo with these bits on when I bought my Duke, and should've just taken that one instead.
Long story short, it wasn't the 390 motor's fault, but rather the mods I had. Specifically in my case both the original and replacement motors failed after the open airbox lid.
Not due to it though, rather due to incorrect fuelling, so not adjusting for the lid after fitment. Took me two failures to realise. Go figure.
Not adjusting - not for air leaks around filter/lid but rather for added fuel, richening it up? I expect it would have been running pretty lean then, probably quite responsive/powerful but at a cost...
After reading everything here and on the RC forum, I had the Akra map flashed on delivery but that even felt lean so I went with PCV from Chad... I need to flash an updated map now that I'm running aftermarket exhaust, this is a good reminder for me to do that soon.
Truthfully I don't know. It's my main form of transport, so I don't want to mess with it too much anymore, having spent $3,000 US on repairs already.
That's the blue pill, the red pill is I now know how good it can be, and will always miss that. Closed loop fuelling being the main concern.
So, for a start, I'll likely only run Kev's closed loop black box with the Akrapovic fuel map. Might add the Bazzaz or maybe RapidBike Evo later on, but not sure yet.
Good to see you back Johann ! Sorry to hear about your multiple failures , but as Will already stated nothing more than that . Engine fuelling is a delicate matter , hence I fitted the Rapid Bike EVO which autotunes to avoid such errors .
Stating the perfectly obvious, the last thing you want to do with these already-lean-from-the-factory engines is to lean the mixture out further by adding more air. Still, I don't see how anything in the fueling could contribute to shearing flywheel bolts. Sounds like somebody (at the factory?) failed to torque them to spec. Or it was assembled with bolts of inadequate hardness. I don't recall hearing anything like that even back in the day when insufficient 2-stroke oiling sometimes caused total engine seizure.
Hey guys, I think I'm back, fell off the edge of the map for a while there. Sorry.
So my Duke is now on its third major failure, first was a BHG, then my flywheel sheared its bolts and destroyed the stator side of the motor.
Bought a lower mileage motor from eBay and it failed three months later, not sure what's wrong there, but I was a bit over it TBH, hence me disappearing for a while.
a more than big enough tale of woe to dampen pretty much anyone's enthusiasm. More details would be interesting but perfectly understand if you just want to draw a line under it.
Not been on here myself for nearly a month but for a rather different reason - I'm now driving for a living, so no computer access during the day (really don't miss it) and much less inclination to web surf when I get home.
Yes. Picking my bike up tonight, after the battery went dead too, so fitting the replacement (just a standard gel acid battery, no money for better).
FWIW the last failure was a dropped exhaust valve, which then speared straight through the piston. Go figure. Don't overrev kids! Especially looking at you lot with the piggyback ECUs.
Welcome back, Johann! Hope things go better for you henceforth. You've had some tough lessons. Your experience is a cautionary tale for those who want to mod their 390 imprudently or thrash it unmercifully. Bottom line: This engine is already highly tuned as delivered. Treat it with respect. Be wary of intake and exhaust mods, especially if you don't have a fuel controller. Avoid extreme RPM's. Change oil frequently.
This, this, and this. Better I learn on a 390 than a 1290. Feel somewhat like getting the new 390, although extremely unlikely unless I was pretty much handed one.
Anyway, after a new battery she runs again, but I have the now infamous idle stalling problem again, the very thing that started me on my engine tuning path.
What was the consensus again to fix it? Side stand switch? Akrapovic fuel map?
Johann, The sidestand switch fix developed by John Wayne and Hoover is simple - first clean both the magnetic bolt and the switch itself. Then take the magnetic bolt off of the sidestand, place a washer underneath it and re-attach it to the sidestand. The washer will now hold the bolt closer to the switch when the sidestand is retracted, so the magnet will now operate the switch more decisively. This fix seems to work quite consistently.
Yep, I've not had it happen a single time since. ( I still pull up on the right at stop signs though!!).
It does get dirty down there, so I wipe it off fairly frequently. The other option would be to bypass the switch all together.
Johann, It sounds as though your throttle cable may be out of adjustment, with too much slack allowing the butterfly arm to drop past the position needed for starting. Tighten the cable slightly (by backing the cable sheath AWAY from the cable perch) and try starting. Repeat this in small increments until the bike starts without need for you to touch the throttle. The butterfly will now be in the correct position, and you will no longer need to crack the throttle to raise it into starting position.
I'm curious where you've heard this tactic? I haven't looked at the Duke's TB in particular but that is a VERY odd design if this is truly the way it's set up. In a good number of years of cars and bikes I've never heard of a system such as that. I'm curious if you've perhaps obtained this from an invalid source.
Idle is typically controlled by a by-pass valve (by-passes the butterfly). The by-pass valve on older vehicles was controlled by a screw, called the idle screw. This screw either adjusted the butterfly stop itself or it adjusted the air flow around the throttle body (via an idle bypass passage). In newer vehicles, there's a stepper motor which adjusts this so the ECU/PCM can control the idle. This is useful for giving higher idle at start-up, without adjusting it manually once it warms up, so it can idle low once warm. Given that I've read else-where that the idle can be adjusted via the ECU and that in the KTM throttle body explosion diagram part # 90641072000 lists the idle adjuster motor, I'm going to say the idle is controlled by the ECU in this case. I've never seen either A. A case where the ECU controls idle AND the person has further adjustment for idle, nor B. A case where the idle is somehow dependent on throttle free-play. In everything I've ever seen on all types of vehicles the idle is determined solely on the butterfly stop, which as mentioned can be controlled by many things, none of which I've ever seen be the throttle.
The manual here suggests that the throttle will have 3-5mm of free-play, which is pretty normal for bikes. manualslib.com/manual/584624/Ktm-125-Duke-Eu.html?page=144
If this KTM manual is indeed accurate this freeplay indicates that it's not possible for the throttle cable to be preloaded, as you're suggesting.
malJohann said:
Awesome thanks. Another problem, I need to slightly crack the throttle for it to start. Any ideas? I thought cracking the throttle at startup cuts the fuel?
Regarding the issue of needing to crack the throttle, first I'd adjust the throttle to specification (3-5mm of freeplay in the throttle). Secondly, if you have a piggy-back I'd remove it temporarily and see if problem persists. Just for testing. ECU might have to recalibrate idle, so remove it for a week or few before you declare it "doesn't fix problem."
If the aftermarket ECU/piggy-back is the culprit I'd bump the idle up a bit in the software (solely in the software). If the software allows control of a "cold idle" or "warm-up idle" specifically I'd increase it there. Hot idle won't matter much unless it's having issues there too. If that does not help or the idle is already sufficiently high (I think it's 1500-1700 hot on this bike) then the mixture is most likely off, and the fuel should probably be bumped in the low throttle/load vs low RPM section of the fuel map (or start-up tables if it has them). Rich conditions work nicely for starting vehicles.
Really crazy what kind of experiences you had. I can see why you'd wanna throw in the towel with it. I would have already, lol. Though if it's a mixture problem it's easy to see why it'd be running hot as piss if it was running lean and cooking engines. Glad ur sticking with it, I absolutely love this bike.
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