Hello to everebody,
three years ago I bought a beautiful yellow K100 built in 1983 S/N 381. I liked very much to ride it in the steep turns of my Liguria land, very close to the sea ... beautiful at all, specially with a very nice lady in the back ...

But last year I had a problem that, up to now, I did'nt solve.

The problem !

Just after half an hour of run, when the engine rpm is below 3000 rpm, the engine does not accelerate properly, it seems that only 3 cylinder are running, acceleration is irregular and slow.

As soon as the engine pass 3000 rpm, the sound of the engine became very very nice ... uaooooooo

I did some checks and accessories change without any result :

- spark cables
- spark igniters
- Fuel electronic unit
- spark coils
- fuel pipes inside the fuel tank

Nothing at all ... I'm very depressed !!!

Have you any idea, any indication ? Summer is coming and I would like to run again with it (with the nice Lady too!)

Ciao ciao

Ugo

I am sure there will be plenty of suggestions but mine is one of the Hall effect sensors on the front of the crankshaft.
I believe they can break down when they get hot.
Would give a similar effect to one faulty coil.

I'm with CJ, or maybe the timing is off?

If the engine is always running good when cold, you should try this:
When the engine is cold, remove the cover of the Hall effect sensors and heat up the sensors with a hair dryer. The sensors are rated for a temperature up to 160 degrees C. You could easily heat them up to 90 degrees. When they are hot try to start your engine and see if it is still working correctly. If it's not, you found your problem.
If the engine is still running OK, I would check the water temperature sensor.

CF

Have you any picture showing the Hall effect sensors location and how to reach them ?

In my Maintenance Manual no mention of them ...

Thanks !

Ugo

Behind the 'T' shaped engine casing, front of engine, just above water pump. Has 5 bolts securing it.
Be careful if running the engine with this panel removed. Can give a nasty shock.

I put this out as a question, Hall sensors go wrong and they are then heat sensitive, this problem comes up when the bike transitions to warm BUT it is only up to 3000 after that it becomes very smooth. Would a faulty Hall sensor do that wouldn't it be faulty at all revs?

I am wondering if we are looking at wear in the air flow meter it is an 83 after all said and done and the upper reaches of the wiper track would be relatively less worn than the bottom bit. Thoughts?
Regards,
K-BIKE

I would expect the problems with the Hall sensors to become worse at higher revs, however, as the ignitions become closer after another maybe less noticeable? Further riding below 3000 rpm at normal speeds should keep the engine cool enough unless lots of standing still/very low speeds to get the hall sensors warm enough to get into problems I would think. However, I have been chasing my tail before on these ones.

I don't know if there's another K close by where you can exchange some parts with? The AMM is a possibility. We need to get a bit more info I think.

Hi there, had a similar problem on mine, runing very rough up to 3000 rpm then smooth, the reason was a miss setting on the idle fuel/air adjust, the air bypass screw at the AMM. Here youl find a setting procedure http://skylands.ibmwr.org/tom/tech/co-setting.html
Best regards
JAP

Hi JAP, very nice hearing from you, only one thing :

my problem appears after half an hour that the engine runs, it seems correlated with engine temperature ... it happened you too ?

thanks e ciao !

Ugo

ugo2011 wrote:Hi JAP, very nice hearing from you, only one thing :
my problem appears after half an hour that the engine runs, it seems correlated with engine temperature ... it happened you too ?
thanks e ciao !
Ugo

Never noticed time, but as the mixture is temp controled both thinks can be related, have you measured the temp at wich the fail starts? as per your first post it happens afther half an hour runing on the way, by that time the engine should had been at working temp for at least 15 minutes, is it very cold were you are riding? if your thermostatic valve is not working propperly and it is very cold outside maybe you are not keeping working temp. Just guessing
Best regards
JAP

japuentes wrote:Hi there, had a similar problem on mine, runing very rough up to 3000 rpm then smooth, the reason was a miss setting on the idle fuel/air adjust, the air bypass screw at the AMM. Here youl find a setting procedure http://skylands.ibmwr.org/tom/tech/co-setting.html
Best regards
JAP

JAP, can you remove the period after the link? It causes an error otherwise.

Hi club_c,
All done well spotted.
K-BIKE

K-BIKE wrote:Hi club_c,
All done well spotted.
K-BIKE

Thanks K, I was out and couldnt do it from the BB
Best regards
JAP

japuentes wrote:
Never noticed time, but as the mixture is temp controled both thinks can be related, have you measured the temp at wich the fail starts? as per your first post it happens afther half an hour runing on the way, by that time the engine should had been at working temp for at least 15 minutes, is it very cold were you are riding? if your thermostatic valve is not working propperly and it is very cold outside maybe you are not keeping working temp. Just guessing
Best regards
JAP

No Jap, is not very cold, in this period Outside Ambient Temperature is about 15 °C, but also last year, during summer time, when OAT was around 25-30 °C, I had the problem after just half an hour. Half an hour is a sort of constant time, I guess some electronic circuit or component problem.

Probably this week I will try to heat the Hall sensor and, if still necessary, to change the Fuel Ignition Unit.

Ciao ! Ugo