Wetting plugs and poor idle....

[Infectus-Guy]

It's been off the road for years. I just cannot get this damn thing running properly. I used chatgpt to document everything I've tried so far. I haven't dared touch the TPS yet, but I guess it's something I could try before I throw this thing on Marketplace and be done with it.
Thanks for any ideas.....


Fuel system

Fuel quality

Fresh super unleaded fuel fitted.

Fuel pressure

Dynamic pressure checked.
~33 psi at idle.
Pressure rises slightly with throttle.
Considered within expected range.

Fuel pressure regulator (FPR)

Vacuum hose checked.
Smoke test performed — no vacuum leaks found.
Vacuum hose removed and inspected — no evidence of fuel bypass from a ruptured diaphragm.
Return path to tank confirmed.
Previous tank non-return valve removed/gutted due to suspected restriction.

Injectors

Injectors recently cleaned.
Injector coil resistances checked — all within specification.
Bike injectors and spare injectors compared.
Both sets marked A46-00.
Spare injector set available for future swap test.
Injector leakage/sticking not yet ruled out.
ECU / wiring / sensors

ECU

ECU identified as Kawasaki 21175-1053.
No stored fault codes.

ECU grounds

ECU black/green ground to battery negative: 0.3 Ω.
Sensor ground to battery negative: 0.5 Ω.

Engine temperature sensor

Resistance checked.
Within specification.
Grey wire resistance to ECU checked — no excessive resistance.

Air temperature sensor

Resistance checked.
Within specification.
Blue signal wire to ECU checked — minimal resistance.

Throttle position sensor (TPS)

Potentiometer resistances checked.
Within specification.
Actual TPS adjustment/position still not confirmed.

MAP sensor

Vacuum test performed directly on sensor.
Output measured:
5 inHg → 1.9 V
10 inHg → 1.5 V
15 inHg → 1.2 V
20 inHg → 0.85 V
Output change was smooth and linear.
Vacuum hose and plenum take-off checked — clear.
MAP sensor held at ~20 inHg during running:
Exhaust smoke reduced.
Idle quality improved.
Ignition system

HT leads / plug caps

Resistance checked.
Within specification.

Spark plugs

Plug types currently fitted:
2 × new BR9EIX.
2 × low-mileage BR9EIX.
Plugs cleaned.
Spark checked with plugs grounded to engine casing.
Spark appears good after cleaning.
Swapped plugs into cylinder 3 — fault remained.
Engine condition

Compression

Compression test completed:
All cylinders between 116–130 psi.
No single cylinder showing a major compression failure.

Vacuum leaks

Intake/FPR vacuum system smoke tested.
No leaks found.
Current symptoms / observations

Engine:

Runs poorly immediately from cold.
Rich smell.
Black exhaust smoke when revved.
Poor/lumpy idle when warm.

Cylinder-specific:

Cylinder 3 exhaust header significantly cooler than others.
Cylinder 3 plug wet with fuel.
Other plugs dry but sooty black.

Vacuum/MAP behaviour:

Unable to obtain a meaningful idle vacuum reading using gauge teed into MAP pipe.
MAP override test (forcing ~20 inHg signal) improved idle quality and reduced smoke.
Current unconfirmed suspects / next logical tests
Cylinder 3 injector
Swap with another cylinder to see if fault follows injector.
Injector leakage/sticking still possible despite resistance being correct.
Cylinder 3 ignition under compression
Plug swap has been done, but HT lead/cap/coil output under load not fully eliminated.
Actual engine vacuum
Confirm gauge connection directly to MAP vacuum source.
Determine whether low vacuum is cause or symptom.
Throttle body condition
Throttle plate position.
Synchronisation.
TPS adjustment.
Injector pulse width
Would determine whether ECU is commanding excess fuel or fuel is entering unexpectedly.

[JezZedexE1]

That is a pretty comprehensive list and covers just about everything.

However, my limited experience and knowledge has picked up two things my bike had which caused similar issues, namely the spark plugs and the fuel tank fuel relief valve.

Use the standard BR9ES plugs and make sure the valve internals are clean and operating as it should. The last issue I was struggling to resolve was spark plugs getting wet and black (with standard plugs) within a couple of minutes of running the engine. Removed, stripped, cleaned & replace the relief valve and runs properly.

I am sure I read somewhere the iridium plugs do not work properly if they are cleaned. Not sure the reason behind that, something about the coating on the electrode. They cannot be cleaned like the normal ones can, using a bit of wet or dry paper.

[Infectus-Guy]

Thanks for your reply. Yeah I've read that about iridiums, though out of the cylinder they sparked much better after a gentle brushing.
Im gonna hit it with the timing gun tomorrow, but I checked that years ago so can't see it being that.
I'm not sure what you mean by relief valve? Do you mean the non return valve in the fitting that returns to tank? I already gutted that and did away with it. I was hoping that was the cause of the overfuelling, but having gutted it and checking the dynamic fuel pressure, I've confirmed that's all good. Maybe the pulse width on the injectors is too high and it's dumping too much fuel? Who knows, but I definitely can't be bothered to scope it!

[JezZedexE1]

This bit on the underside of the tank. Has a small spring and things to control the fuel pressure. Someone might be able to say/advise whether gutting it will help. After cleaning the one on my bike, it was totally different. Problem gone.

Screenshot 2026-07-16 195027.jpg (101.47 KiB) Viewed 669 times

Have you got the fuel filter (new one preferably at this stage) on the correct way? Flow direction is shown on it.

[Infectus-Guy]

Yeah that's just a non return fitting and it doesn't (well it shouldn't) affect the fuel pressure. All it's there for is, so that you don't lose all the fuel from your tank when you remove the pipe.

[rangeroy]

plugs too cold use 8's whilst its on the stand, its not producing boost so no chance of damage (IMHO) when you had injectors cleaned did you have them flowed/cc'ed & are they standard?
good luck

[Infectus-Guy]

Interesting thought ref plug temp, but it runs so badly I almost can't see it making that much difference.
Unfortunately the injectors didn't fit their test rig. I've actually got a spare set, so I'm going to give them a try.

plugs too cold use 8's whilst its on the stand, its not producing boost so no chance of damage (IMHO) when you had injectors cleaned did you have them flowed/cc'ed & are they standard?
good luck

[JezZedexE1]

Yeah that's just a non return fitting and it doesn't (well it shouldn't) affect the fuel pressure.

I understand your thinking, but my thoughts at the time I was doing my bike (I may be wrong here) was that if the fuel flow returning to the tank is partially blocked, the back up may cause a change of something. Either fuel flow, direction of flow or change of pressure somewhere in the line. Possibly the reason for wet plugs. A bit more fuel than required maybe. I may have been overthinking it though.

Whatever the issue was that my bike had, it seemed to have been resolved cleaning the non-return valve.

Likewise, without internal parts in the valve, resistance may be reduced so the flow could be affected, but in the opposite way. Path of least resistance and that stuff.

I do not know if what I have written is plausible or correct, but I do find have input from other sources helps me progress.

Hope you figure it out soon.

[rangeroy]

Jez will be correct over the relief valve if it sticks it will increase pressure & fuelling, not sure why the injectors didnt fit the cleaning rig? seems odd to me & they could be bigger than the normal 240cc as standard so if you have spares try them

[750turboguy]

Wooow.... I mention this alllll the time because no one goes here.

Just because the battery starts the bike, it could have a weak cell. A weak cell will mess up the electronics and cause EXACTLY what you are experiencing.

How's the battery? You indicated the bike has been inop for years. Put in a new battery. DONT JUST CHARGE THE OLD ONE.
REPLACE IT!


After having similar issues several years ago I eventually discovered the problem. Confirm like this with a freshly charged battery.
And make sure each cell is properly filled with DISTILLED water. Why distilled water? Fresh water, even filtered spring water
is full of contaniments and will foul the cells.

Remove ALL the yellow caps. place the black probe of your volt meter on negative and just dip the tip of your red probe into the
cell closest to the negative. Do you get 2volts? Move to the next cell. Do you get 4volts? Then 6, then 8 then 12?

If not. Replace the battery.

Or...try this. roll the bike next to the car and disconnect the bike's battery and using jumper cables connect to your car battery.
DO NOT RUN THE CAR. just use the battery. If the problem is the battery, the bike will run on the car battery. Now..connect you meter to the red and black at the bike and rev the engine just a bit...not too high. Does the voltage increase? If so, the alternator is pumping out
juice. Hope this helps.....

And one more thing....... DO NOT TOUCH THE TPS. If it was running well before, there's no need to adjust it.

[Gibsones295turbo]

Wow, sounds exactly like mine.
Mine was sitting for a few months and ran crap & was smokey. Had a new turbo fitted and changed the valve stem seals, new genuine rings, and a re- hone.
Its stopped the blue smoke but now its running really rich and not very crisp & a slight mis fire.
I put my old iridium plugs back and checked most of what you have done.
Once its hot it improves a bit. But not much.
I am going to take it for a gentle thrash tomorrow to see if it cleans itself out a bit.
Like someone else mentioned here, i may remove the fuel return valve in the tank and see if its causing too much back pressure.
Did you replace valve stem seals? They may be worn.
I reckon an old bike left standing for a while gumms a lot of fuel related parts up.
I was also wondering about my new HT caps, as they Dont have a 5k resistance in them ! Not sure if that would make a difference though.
I will also re check my engine temperature sensor tomorrow and see if its reading correctly as I'd assume that that may cause a rich mixture.

[Infectus-Guy]

Yeah the battery is brand new and fully charged with good voltage. Thanks for the suggestion though, often overlooked.

[rangeroy]

race mode enabled?