Reaching out for new ideas. Dying idle problem.

[Shadowwolf1117]

Here is the quick of it, those of you that know me know I am a kawi mechanic for a lot of years. Hence the frustration for the following issue.
2007 Ninja 250, no mods no upgrades. 30k miles, always maintained. Sat for 1 month, typical idle choke issues, rebuilt carb to specs and perfection, starts idles with choke to 3500 rpm, shut off choke, idles same, touch nothing and it will slowly drop off and die. New plugs, carbs are sync'd air fuel jets are dialed in valves are to spec intake boots on airbox and head side are clean no tears or cracks, fuel is super fresh running all diagnostic tests on iv bottle so vacuum petcock and tank is eliminated. At a loss guys, open to outside of the box thinking. FYI also did compression test and leakdown, all to spec super strong. Thanks for any insight.

[Skid]

Disclaimer: I have turned a few wrenches but not much on motorcycles. Just throwing some ideas out there since you asked.

Sounds like the motor is leaning out - so a fuel issue of some sort. Have you checked the float needles and level?

Dirty fuel filter?

[davenay67]

Is the engine dying in corellation with the engine warming up..?? In other words, will it die like this every time it gets to a certain temperature..??

It does sound like a fuel issue from how you describe it. When it's dying, perhaps you can blip the throttle and see if you can get a sense of whether it's lean or rich at that point in time....

[Shadowwolf1117]

First address. float levels seats and needles are set and clean
Second address. the warm up temperature is not indicative to the stalling issue, i allow it warm up enough to raise temperature to close choke, and yes "blipping" the throttle will keep it running. but closing the throttle will allow it to idle high around 3k and then slowly plummet to a stall. so although fuel seems to be the culprit, mild throttle massaging will keep things running. If there was a fuel pump I would look to blame it, but there isnt, just a vacuum petcock, which as mentioned before is currently out of the equation given the fact I am on an iv bottle.
Keep the ideas coming guys there will be someone with something that will make us all go "Hmmmm maybe" but until then I am a bit stumped.

[dirty nasty]

Hanging and high idle? Sounds lean to me. Have you adjusted your fuel mixture screws properly? The bike should sit at 1300-1500 RPM at idle.

[Shadowwolf1117]

Yes air fuel screws are set proper, and carbs are sync'd. and yes everything points to lack of fuel but nothing indicates such on diagnostic. Cannot seem to pinpoint where the fuel lack would originate.

[cuong-nutz]

Sticking slides? Pinched rubber thing that goes over slides?

[dirty nasty]

What about those small silver guides that the needles slide into? I had mine in wrong and the bike ran really weird. They can fall out easily and are hard to keep track of.

[alex.s]

after it dies have you checked how much fuel is in the carbs. are they low? could the float valve be getting stuck closed? what about battery levels? after it dies can you easily start it right back up? or does it stumble trying to start back up until you rev it a bit? maybe one of the stator coils is bad and its not charging enough and when it sits idling the spark gets weaker until it dies? i guess that would only really make sense if it suddenly stopped... the fading to off and hanging makes it sound like its just not getting enough gas ... can you hook up some kind of flow meter to your gas feed?

did you soak the carbs? maybe an internal passage is partially blocked

[Shadowwolf1117]

Originally Posted by alex.s

after it dies have you checked how much fuel is in the carbs. are they low? could the float valve be getting stuck closed? what about battery levels? after it dies can you easily start it right back up? or does it stumble trying to start back up until you rev it a bit? maybe one of the stator coils is bad and its not charging enough and when it sits idling the spark gets weaker until it dies? i guess that would only really make sense if it suddenly stopped... the fading to off and hanging makes it sound like its just not getting enough gas ... can you hook up some kind of flow meter to your gas feed?

did you soak the carbs? maybe an internal passage is partially blocked

To address all the carb questions, they are virtually new now after all the meticulous cleaning and checking, float levels are spot on and the gas in the bowls are still at capacity after stalling, so fuel pressure and flow rate seem to be spot on. Battery is new and charged and restarting the bike is no more difficult than its original start before the fade to stall. you make an interesting point about the coil, we have been adressing loss of fuel but what if it is loss of spark, now the plugs are new and gapped correctly, I even swapped a couple of new sets to eliminate the proverbial "bad new" part. Im going to check spark levels next and see if perhaps a coil is to blame, understanding it would simply cut out and not slowly drop whose to say that maybe the stator is still engaging the "remaining" spark after the coil dies. Im not sure if that evenmakes sense but I will test spark duration and post up soon.

[Shadowwolf1117]

Originally Posted by cuong-nutz

Sticking slides? Pinched rubber thing that goes over slides?

Slides are superbly clean and move effortlessly and the diaphragms are in pristine shape no tears or stress cracks or anything.

[alex.s]

You might want to check all the coils just to be safe... Main plugs, crank pickup and stator. A faulty crank pickup can do some really funky things and they are all really easy to test... At least you can cross them off the list

[greg737]

What about those small silver guides that the needles slide into? They can fall out easily and are hard to keep track of.

Did you verify that the needle seats are still in the carbs?

Also, I've seen unexplained lean conditions caused by vacuum leaks on older fuel injected cars (old Alfa Romeos with SPICA fuel injection have problems with leaks in the rubber connectors between the throttle body and engine). So your carbs could be absolutely perfect but suffering from a vacuum leak situation that gets worse when the connector boots warm up and soften a bit.

[alex.s]

are there any small children or animals living in your airbox

[Shadowwolf1117]

Originally Posted by greg737

Did you verify that the needle seats are still in the carbs?

Also, I've seen unexplained lean conditions caused by vacuum leaks on older fuel injected cars (old Alfa Romeos with SPICA fuel injection have problems with leaks in the rubber connectors between the throttle body and engine). So your carbs could be absolutely perfect but suffering from a vacuum leak situation that gets worse when the connector boots warm up and soften a bit.

Vacuum lines were replaced when I first redid everything given that they were split, but vacuum has been solid during this entire mystery. I will inspect the coil and pickup stats tomorrow (tuesday) and post up...thanks

[Shadowwolf1117]

Originally Posted by alex.s

are there any small children or animals living in your airbox

Evicted years ago lol, all things clean and breathing well

[alex.s]

was it rebuilt on an indian burial ground where you dug up corpses to piss on them and make funny movies with them before burying them back in the ground again, but upside down after you baptize them?


...yes... these questions need to be asked for the sake of a proper diagnosis.




but seriously though.
lets go through the checklist...

fuel supply: good
carbs: good
air supply: good
electrical supply (battery) and charging (stator): good, and good(?)
electrical timing (CDI, pickup coil): good
main coils, plug wires and plugs: good
valve clearance and timing: good and assuming good
compression: good.

hmm...

maybe its some kind of clutch issue... like the clutch is dragging too much and its just stalling... have you taken the engine bottom end apart?
if its not some kind of mechanical drag, maybe at the low speed idle, the vibration is just right to vibrate a wire into shorting or cutting out? have you checked the entire wiring harness for any wire breakage?

[flynjay]

Might sound a little to simple, but have you adjusted the idle up a little bit? What is the lowest idle that you can maintain without choke?

Are the valves in spec?

[alex.s]

do you have an air fuel gauge? maybe you can install it and get a sample of it while it dies and see if its dying from fuel or from something else

oh! maybe theres something hiding in the exhaust!

[Shadowwolf1117]

Ok here is the latest update responding to the last bunch of ideas, and there were some good ones,

Timing and pickup coil checked and good within tolerances
Plugs new and good
Valve clearance timing and compression all in spec
I checked the exhaust and all clear.
I did not take the bottom end apart.
Clutch drag inspected, all free spinning no drag.

Response to the idle question, idle set screw is mild but does not affect the dropping off and stalling it simply either kills the engine completely on turn out or increases the already high 3500 rpm idle to even higher. and that is with very mild turns.

Air fuel gauge 20lbs vacuum even across the board and sync'd perfectly.

Next?!

[flynjay]

Originally Posted by Shadowwolf1117

Ok here is the latest update responding to the last bunch of ideas, and there were some good ones,

Timing and pickup coil checked and good within tolerances
Plugs new and good
Valve clearance timing and compression all in spec
I checked the exhaust and all clear.
I did not take the bottom end apart.
Clutch drag inspected, all free spinning no drag.

Response to the idle question, idle set screw is mild but does not affect the dropping off and stalling it simply either kills the engine completely on turn out or increases the already high 3500 rpm idle to even higher. and that is with very mild turns.

Air fuel gauge 20lbs vacuum even across the board and sync'd perfectly.

Next?!

You said you have it on an IV bottle for fuel. Did you plug the vacuum line that goes to the petcock? It sounds like either your idle mixture screws are all the way in or you have a vacuum leak.

[Shadowwolf1117]

Originally Posted by flynjay

You said you have it on an IV bottle for fuel. Did you plug the vacuum line that goes to the petcock? It sounds like either your idle mixture screws are all the way in or you have a vacuum leak.

Yes its on an IV bottle so obviously petcock is out of the picture, vacuum lines are run to the merc sticks, no vacuum leaks. Idle screws set to 3.25 turns out, they are just fine.

[Shadowwolf1117]

Upon massively close scrutiny there "appears" to be some unusual scarring around the intake ports on the head itself. If nothing new presents itself in the next day or two I will disassemble the head and have it magna fluxxed for possible hairline crack. Will keep you all posted...thanks