1987 K100RT with a gazillion miles
I’m experiencing a very minor - but consistent - missing until the engine is completely warmed up (usually 10 miles or so) at which time the missing goes away.

I want to stress the missing is very real - I can feel it in my right hand grip - but the missing is not as pronounced as if I pulled a plug wire. 

I am ready to start troubleshooting but by the time I am back to the garage (more than 10 miles), the missing has disappeared. As long as the bike is warmed up, the missing does not rear its head.

The bike starts and idles without issue (although I believe a “minor” miss may be difficult to detect at idle.

Miss is more difficult to detect under hard acceleration (before engine is fully warmed up) than it is at steady speed.

This is a new thing in my life. I considered an injector not performing up to spec (but not plugged) so I am running a tankful of Chevron to see if their Tektron will clean out any semi-plugged injector.

Ideas, suggestions, hints, etc. are appreciated.
Dave

First thing, check carefully for air leaks, especially the Z tube.  Possibly one of the caps on the throttle body vacuum ports.

A small leak will make the mixture a little too lean when the engine is cold, but let it run better when it warms up and can run on a leaner mix.

How did you resolve that knock that was happening back in March, Dave? You ghosted that thread.

I had an Audi coupe with plenty of miles - exact same symptoms - just a very slight misfire on tickover, nothing under load.
Worn valve guide was the problem - on a compression test you could see the faulty cylinder 'missing' as the valve occasionally failed to seat and the needle 'missed' a flick.
Hope it's not that, but just something to consider.

No apparent air leak - sprayed stater fluid around the various tubes, hoses, connections and sealed vacuum ports with no change in RPM.

Spark plugs look good (and they were replaced 200 miles ago), verified valves were within spec, and I did a compression test (170-180-175-170).



Next step? Hey, maybe ‘next step’ is to wait and see if a tank of Tektron makes a difference.

Dave

Laitch wrote:How did you resolve that knock that was happening back in March, Dave? You ghosted that thread.

I did not intentionally circle back on this knocking post. The knocking may have been just the dreaded output shaft - in which case I have decided to just turn down my hearing aids until the bike warms up.

One thing I noticed was one of the spark plugs had a 1K Ohms resistance. The other three plugs had zero resistance. The plugs were very recently replaced (as a set). I am not sure if this resistance would cause a problem, but nevertheless replaced the plug.

Ah, another case of self-inflicted pain. If someone would just take my tools away from me, I believe my problems would disappear.

The problem was the timing was off. About a month ago I had an occation to remove the timing chain (another story for another time) and when reinstalling the chain I was very focus in insuring the cam gears were perfectly aligned with the case markings. What I was not so focused on is keeping the engine at TDC when aligning these two gears. In retracing my prior work, the cam gears (which were still in perfect tandem with each other) were off maybe two teeth when the engine was brought back to TDC. Correcting this “minor” oversight, resolved the missing notion. Problem resolved.

All was not lost, I did replace the little 3W bulb in the fuel gauge.

As always, thanks for everyone’s help.
Dave

A gazillion is somewhere between 230,000 and 240,000 miles. I’ve had it since 2003 when it had 86,000 miles on the clock. I keep changing the oil and it continues to go down the road. Can’t say for sure on the mileage since I have had the speedo gears replaced twice and there was a couple of years where the odometer wasn’t odometering.

it may just be getting a little worn even for a k100 

Yes, I agree.  I keep taking her temperature (compression, leak down test, etc.) to give me an idea how the old girl is doing. So far, so good.

davemadsen wrote: Ah, another case of self-inflicted pain. . .  .I keep taking her temperature (compression, leak down test, etc.) to give me an idea how the old girl is doing.

Could this in fact be a rare case of MMSBP?

Motorrad Munchausen Syndrome by proxy.

Never!