Hi all,

I recently picked up my first K, a 1984 K100 RS and have some troubleshooting questions. On the ride home, she stopped on the highway.
The throttle cut out, similar to what you'd expect when you run out of fuel. At the time, I thought the engine was overheating, as it was a hot day (~40°C) and the temperature gauge was swinging wildly around the 90/100°C mark. I pushed her off the highway and she started up again about 10 minutes later. I rode off onto a B road, and then she stopped again about a kilometre further. This time I stopped for a good 20min thinking it would let the engine cool down completely. This seemed to help and I got home without any other hiccups.

After some internet research - my symptoms seem to point more towards a clogged fuel filter/bad fuel in the tank, as the bike was sitting for a few months with the previous owner with ~4lts in the the tank. I plan inspect the fuel filter when I run down the current tank of gas.

Which brings me to the my question - I did another ~100kms today, with no issues, but still noticed that the temp gauge swings wildly when on the highway - is this normal?

How easily does the bike start? I would change the coolant and replace the fuel pump and filter, also check the mounting system inside the tank. Mine had rotted and the pump was cutting out. The new mounting and pump have cured the stutter and ruff running.

Stumpy wrote:How easily does the bike start? I would change the coolant and replace the fuel pump and filter, also check the mounting system inside the tank. Mine had rotted and the pump was cutting out. The new mounting and pump have cured the stutter and ruff running.

Bike starts up immediately (even with no "choke") and after about 45 seconds settles down into a smooth rhythm. I did open the coolant tank and notice that it looked more like water than a coolant water mix, will flush it out.

Is the swinging of the meter normal - I notice that it is aggravated during bumps on the road. When parked, the needle seems to be quite stable.

PS: It's this guy - just to be sure:

It might be worth checking where the gauge is wired to as I'm pretty sure the early RS didn't have a temp gauge fitted, but I might be wrong (I normally am!)

Dave

ashthespy wrote:
Is the swinging of the meter normal - I notice that it is aggravated during bumps on the road. When parked, the needle seems to be quite stable.

In a word - no. Normally the temp needle is very stable, rising or falling slowly and steadily with temperature changes.

I have noted erratic swinging of the needle on a couple of occasions - both were down to the imminent breaking of one of the wires to the gauge. The gauge is mounted reasonably firmly, but the wiring isn’t and does flex as the bike jolts along. Over time, this can cause the wire to break completely, but can give intermittent readings as it makes and breaks contact just prior to giving up completely.  Easy to check and easy to fix...find the errant wire, cut back and affix a new connector.

As for the cut out when running, cooling down and runs again...that sounds like a Hall effect sensor issue. Type Hall effect sensors into the search bar and see lots of good advice and suggestions. Fuel pump/filter/stale fuel issues wouldn’t get better with cooling down.

Davep wrote:It might be worth checking where the gauge is wired to as I'm pretty sure the early RS didn't have a temp gauge fitted, but I might be wrong (I normally am!)

Dave

They didn't - but it's pretty easy to retrofit one to an 84.

Check the wiring.  If the insulation is chafed and intermittently grounding then that will cause the gauge to spike.

ashthespy wrote:The throttle cut out, similar to what you'd expect when you run out of fuel.

Did it sputter and die (like running out of fuel) or just die instantly?

Thanks for the tips everyone, will look at where the gauge is wired into and get back.
Will also do some research on halleffect sensor now! :-)

duck wrote:

ashthespy wrote:The throttle cut out, similar to what you'd expect when you run out of fuel.

Did it sputter and die (like running out of fuel) or just die instantly?

Hmm, good question, I am not entirely sure - I just recall no response from the gas, and then the bike not starting up when I was costing to the shoulder to pull off. When it did start on the highway, it would only idle, and any throttle would kill the engine.

FWIW, I did another ~100 kms today on the moterway with no issues, so I wonder if I just had some 4 month old gas sitting in the tank..
I unfortunately don't have access to my workshop/tools, as I just moved to the country, but will try to find a place to get the filter out and give it a gander..

If it's the hall, it needs around 30 minutes to restore itself.
If you can start after 10 minutes, it's not the hall.

Also check the tankbreather system.
If the bike stalls, open tank, should start right away.