Hello Ladies & Gentlemen,

90,000 miler, was reliable until sprag clutch cried 'enough'.

I've ridden the last 40,000 miles on this and plugs have always been changed at every 3k service. 
Just recently I replaced some more parts to try and cure what looked like an air leak on C4.
I took a short run to get fuel and this is what the new plugs look like after 8 miles.

I'm close to thinking this might be the end of the road for this engine.

Thoughts..?

I would do compression and leakdown tests before tossing in the towel on that engine.

What year K100 is this?  Do you park on the side stand?  What oil are you using? What is the oil consumption?  What is the oil level?  What kind of fuel mileage are you getting?  What did the last set of spark plugs look like when you pulled them out?

At 90,000 miles I would expect a stuck injector putting too much fuel in the cylinder before bad rings or valve guide seals letting it burn a lot of oil.

My money is injector related, top of the list. Then valve clearances. The engines are unburstable and rarely an issue.

I had similar on my 84 RT at about 87k miles. Injector issue. Cleaned etc and sorted it.

do not discount bad ignition cables , thimbles ....or even the bad plug , a few have seen almost brand new plugs fail , i say few .
 do not let bad cables reside in there too long , could affect the coils long term ..

Point-Seven-five wrote:I would do compression and leakdown tests before tossing in the towel on that engine.

What year K100 is this?  Do you park on the side stand?  What oil are you using?  What is the oil consumption?  What is the oil level?  What kind of fuel mileage are you getting?  What did the last set of spark plugs look like when you pulled them out?

At 90,000 miles I would expect a stuck injector putting too much fuel in the cylinder before bad rings or valve guide seals letting it burn a lot of oil.

Hello, thanks for the comments..

Here's some additional background:
K is 1990
Occasional side stand, but stays on centre stand  in the garage.
10W40 Semi Synth oil
Injectors were serviced by Injectortune 2014. 3 passed all spraying 165cc/min. 1 failed and was replaced by another used. 
Oil consumption negligible.
45 -50 MPG regularly.

Might have to dig out the compression tester...

Thanks all.

Besides the condition of the plugs, what are the engine performance symptoms you're attempting to mitigate? What indicated a possible air leak?

#4 is the only one that looks normal, but it is hard to tell from pictures. I would do the easy stuff first, check the coils & coil wires for proper resistance. Also the temperature switch to see if it is working properly. Do a bit of searching on this site as there is lots of info on how to check things out, before you start throwing parts at it.

The symptoms show that it is running rich but is that because of poor ignition or too much fuel. You mention an air leak, that would tend to make things run lean, not rich. Have the plugs always looked like this or is this something resent.

Great! Thanks for the reply with information.

First, what did the old plugs look like when you pulled them out?

If the oil consumption is negligible, I doubt that the problem is oil fouling.  Your rings and valve guide seals are probably okay.  

Side note: My 16 valve K100RS's use a lot of oil compared to my 2 valve versions.  Around 1 quart every 800 to 900 miles.  My other bricks will go over 2,000 miles on a quart of oil.  The high consumption is most likely due to the 10w30 full synthetic that I am using in them.  It's been said that synthetic, especially in the lower SAE grades, gets past rings and seals more easily than Dino oil.

Six years is long enough to have some crap get into the fuel system and stick an injector.  My experience is that idleness is what messes up fuel injectors on bikes with good fuel filters.  Even if the bike hasn't been sitting for a long time something could be hanging up the pintle.

You might want to pull the injectors for cylinders 1 and 2.   Run some carb cleaner through them.  There are cheap plastic fixtures that go on a can of cleaner and allow you to blow it through the injector.  This would be an easy and safe way to see if they're stuck open, and possibly clean out whatever may be causing the problem.

History of injectors is enough for me to say, that's were the problem lies

moriarti wrote:History of injectors is enough for me to say, that's were the problem lies

I accidentally put diesel in my K1100LT on Christmas Day.

39k miles on it, it had been running fine. I got most out and topped up using E5 petrol and figure remaining fuel to be about 10-12% diesel. It ran a heck of a lot better, like I had changed injectors. No need to even take out the injectors for the first shot.

I agree on going for the injectors, but try a 10% diesel in the gas tank. Agreed to on the plugs, I often had dud plugs straight out of the box. But replacing HT leads, if they are original, is a good move and not expensive.

92KK 84WW Olaf wrote:

moriarti wrote:History of injectors is enough for me to say, that's were the problem lies

I accidentally put diesel in my K1100LT on Christmas Day.

39k miles on it, it had been running fine. I got most out and topped up using E5 petrol and figure remaining fuel to be about 10-12% diesel. It ran a heck of a lot better, like I had changed injectors. No need to even take out the injectors for the first shot.

I agree on going for the injectors, but try a 10% diesel in the gas tank.

Reminds me of back in the 60's when i had a job working in a gas station.  One of the treatments we did to old engines was to take the air cleaner off and pour, that's right, POUR a quart of kerosene(paraffin to the Euros) down through the carburetor while revving the piss out of the engine.

Besides getting rid of every mosquito for a couple miles, this would loosen up and remove a lot of the carbon buildup on the valves, piston face, and in the cylinder.  The engine would run a little smoother, maybe a little cooler, and the pinging from pre-ignition would stop.

The stuff we used had some sort of pine scent in it so that the resulting fog smelled kinda like a smoldering pine tree so the neighbors wouldn't be coming around with pitchforks. Still, we had to watch which way the wind was blowing.

Good shout Olaf,we have used this cocktail in reverse on old diesel motors to clean injectors with good results ,cheap/easy too.

TWB,in the UK we used REDX same thing lots of smoke clean engine innards

Is the vacuum hose to cylinder four cracked or popped off behind, or you replaced it and it's popped off?

daveyson wrote:Is the vacuum hose to cylinder four cracked or popped off behind, or you replaced it and it's popped off?

If its 83-85 there is also a vacuum hose at no 1 to the vacuum sensor in beside the fuel pressure regulator.

Thanks everyone..

Here are answers to the questions you raised, and perhaps this will help someone else browsing in the future..

This K is 1990, and I have replaced the vacuum hoses. 
Previous plug changes have been 'normal' but 4 always lean.
No.4 has always run lean - according to the plug condition and the mercury level - which would never match 1,2 and 3.. (suggesting the air leak) but I've just replaced the intake manifold adaptor, clamps etc. Made no difference evidently..
I have removed and cleaned injectors 2 and 4. Will see if this makes any difference before moving on and doing the others.
The rad is out too. The fan wasn't functioning all of a sudden, so I have just ordered and received a replacement SPAL 7.5 inch fan.
Once that's in I will test run again and close this thread.

Thank you and regards,
Neil.

Did you use sealant when replacing the inlet adaptors - the ones that bolt down onto the cylinder head? That's a commonplace leak in my experience - it is after all on the vacuum side of the throttle plates. Nowadays I never reassemble those adaptors without RTV.

V11POW wrote:This K is 1990 . . .

Is this the LT or the RS?

I'm afraid, but as you probably run on unleaded fuel since 20 or 30 years, the coloration of spark plugs does mean nothing no more about air fuel ratio. It was the lead oxydes resulting from combustion that used to allow hypotesis about the richness or leaness of the mixture.
But no lead in fuel means no lead oxydes.
The only information the color of plugs can give today is about rings and cylinder wear, or the valve guides wear, causing extra oil to get into the combustion chamber.

I spose cylinder four looks like the last one to look at, but I'll do it again. I should have mentioned that after a ride, the vacuum hose should be dry when pulling it from the throttle body. If it's damp the fuel pressure regulator diaphragm is leaking, and excessive fuel is getting sucked in.

If it seemed like it was replaced when you got your brick, the previous owner might have had the problem. If it was a serious leak, the con rod could be bent from hydraulic lock. That would reduce compression on cylinder four. That's a long line of "ifs" I agree, but it's an easy check for fuel in the vacuum hose.

Hopefully it's just a leaking regulator, not a bent con rod. Simply removing the crank cover allows you to look at the con rods.

Edit: as with earlier posts, I'd at least do a compression test.

jbt wrote:I'm afraid, but as you probably run on unleaded fuel since 20 or 30 years, the coloration of spark plugs does mean nothing no more about air fuel ratio. 

Yours is the only post so far in this thread referring to coloration of spark plugs. 

References in previous posts have been about the condition or appearance of spark plugs. Maybe we're just experiencing a language translation glitch. Every major spark plug manufacturer on the planet seems to currently supply webpages with photos interpreting the condition of spark plugs as they relate to fuel mixture or engine performance.

On the other hand, if spark plug manufacturers are posting these photos and descriptions just to comfort elderly consumers like me who don't realize the photos are meaningless and are artifacts of a bygone era, I think it's endearing and I'm all choked—in the emotional, not fuel delivery, sense—up. 

If you swap the injectors and try and replicate the problem on a different cylinder. If the problem does occur on a different cylinder, hey presto, it's injector related - either the supply or the injector itself.

Point-Seven-five wrote:

92KK 84WW Olaf wrote:

moriarti wrote:History of injectors is enough for me to say, that's were the problem lies

I accidentally put diesel in my K1100LT on Christmas Day.

39k miles on it, it had been running fine. I got most out and topped up using E5 petrol and figure remaining fuel to be about 10-12% diesel. It ran a heck of a lot better, like I had changed injectors. No need to even take out the injectors for the first shot.

I agree on going for the injectors, but try a 10% diesel in the gas tank.

Reminds me of back in the 60's when i had a job working in a gas station.  One of the treatments we did to old engines was to take the air cleaner off and pour, that's right, POUR a quart of kerosene(paraffin to the Euros) down through the carburetor while revving the piss out of the engine.

Besides getting rid of every mosquito for a couple miles, this would loosen up and remove a lot of the carbon buildup on the valves, piston face, and in the cylinder.  The engine would run a little smoother, maybe a little cooler, and the pinging from pre-ignition would stop.

The stuff we used had some sort of pine scent in it so that the resulting fog smelled kinda like a smoldering pine tree so the neighbors wouldn't be coming around with pitchforks.  Still, we had to watch which way the wind was blowing.

 
Point-Seven-five, Hello old friend.
Your answer has me in stitches, I think you should take up comedy writing!
Happy New Year,

Lorne

Hey Lorne, good to see you are still around!  Hope you're still riding your bricks.

my 85 rs was running rough..noticed the three covers on the air intake were dried and cracked...replaced them and now it runs like a top.  These are small rubber parts, cost about 3.00 each.

webster wrote:my 85 rs was running rough..noticed the three covers on the air intake were dried and cracked...replaced them and now it runs like a top.  These are small rubber parts, cost about 3.00 each.

You're talking about the three vacuum port caps on the throttle bodies, likely. The fourth one has a hose on it which goes to the fuel pressure thingamabob.