1985 K100 sudden loss of acceleration and super rich mixture smell from exhaust.

dieselyoda

Active member

• Aug 9, 2019

• #1

The bike runs nice, not great.

History: old girl, about 80K miles, routine tune-ups, valves just checked, new plugs, one fuel pump/filter a few months ago.

Up until lately, no complaints but suddenly got lazy and the exhaust smells super rich.

Air filter is great, plugs look good, TB sync perfect, idles steady at 1000 RPM.

My next thought is the timing changed and I have gone retarded a bit. Checked my marks with a strobe, marks align.

Not sure where to go next except advance the timing and risk burning pistons/valves.

 

98lee

3 Red Bricks

Staff member

• Aug 10, 2019

• #2

Yoda,


Try this next. https://forums.bmwmoa.org/showthread.php?93214-Testing-K75-K100-temperature-sensor

Don't advance the spark. That is not the problem.

 

pglaves

#13338

• Aug 10, 2019

• #3

I read the original post and my mind instantly suspected the engine temperature sensor. But I see Lee beat me to it.

 

dieselyoda

Active member

• Aug 11, 2019

• #4

You guys are on to something. The sensor is working but seems lazy or the thermostat is stuck open.

The engine isn't getting very hot, about 150 degrees but I am not sure the reason is the thermostat yet. Pretty low ambients here last few days.

I am a little afraid to bring it up to temperature in my shop without a fan cooling the exhaust but I guess if I remove anything that could melt, I should be OK?

 

98lee

3 Red Bricks

Staff member

• Aug 11, 2019

• #5

Lazy?

Either the sensor exactly matches the water temp throughout the range or it doesn't. If it doesn't, it needs to be replaced. Use your infared temp gun to verify the water temp in the pan for different resistance readings.

Usually you should remove the sensor and "bench test" it in a pan of varying temp water.

If the sensor tests ok, clean the connections at the sensor and at the ECU with DeOxit. Any corrosion at the connections will vary the resistance seen by the ECU which will result in incorrect mixture.

 

dieselyoda

Active member

• Aug 12, 2019

• #6

Still could be the sensor but the thermostat is definitely not holding. Never gets hotter than 150F.

Ordered a new thermostat, 4 weeks away!

 

98lee

3 Red Bricks

Staff member

• Aug 12, 2019

• #7

In stock at EME: https://www.euromotoelectrics.com/product-p/thermostat-716.htm



Don't forget to order the cover O-ring (under options) for $4.

 

dieselyoda

Active member

• Aug 24, 2019

• #8

Fixed-Thermostat

I really wanted to post a picture of the thermostat but I think it wound up in neverland.

Essentially, the thermostat fell apart.

After we got it together, the engine started building and shedding heat. A quick, ginger run around the block and the change was noticeable.

Rode it like I stole it, fan came on, builds nice response and the rich smell as disappeared.

 

98lee

3 Red Bricks

Staff member

• Aug 24, 2019

• #9

 

pauls1150

MOA #24991, south of Los Angeles

• Aug 24, 2019

• #10

A ginger run around the block... that was your passenger?

Interesting coincidence - my neighbor's Kia SUV was having temperature issues, so we got into the thermostat... not quite broken all the way through, but it was about to become two or three pieces.