1987 K75T Speedometer and Fuel Rich

[jtmckinney]

I bought this machine about a month ago and it has been running great until a week ago when it started cutting out and missing. I pulled the spark plugs and #1 was fouled, #2 looked like it was rich and #3 looked just right with the tan color and dry. They were the correct plugs according to the manual, Bosch X5DC. Exhaust looks dry at the tail pipe. It has never smoked and doesn't appear to use any oil. The person I bought the machine from told me he used full choke at cold start and then went to half choke after a few minutes and took the choke off after a few blocks. The manual says to use half choke for the ambient temperatures here in summer which is what I am doing now. I also put Chevron Techron into the fuel approx 100 miles before it started cutting out. Fuel millage has been low to mid 40's.

I plan to remove the fuel tank this weekend and trouble shoot the fan which doesn't work and at the same time I will look at the air filter but I think it is ok.

That the plugs look so different is my question, is this a bad thing?

Also on the way to work this morning the speedometer and millage odometer quit working for a while and then started working again and then quit again before I reached work. The rest of the instrument panel seems to be working just fine.

Any ideas as to the first place to look for this problem.

The trip odometer has not worked from the beginning, I was showed this by the provious owner.

All help appreciated, Thanks
James

[41077]

Intermittent speedo is a common problem on the early K bikes, and has been addressed here before (try a search). There are fixes (not cheep) one of my two K75T's has this issue and I've lived with it for 24 years, works most of the time.
Fuel injectors might be the problem but I'm no expert mechanically.
How many miles on this bike, how many on that set of plugs.
You MPG seems about right, I get closer to 43/44 on my urban commute.

p.s. Welcome to the T owner minority. T production was not continued in 87 something about low sales, at least thats what the BMW rep told me at the 87 show when I asked "where is the T model?" So your 87 T is a leftover 86 sold as an 87, a one year production run makes them kind of rare.

[SheRidesABeemer]

Welcome to the K75 club!

I would strongly recommend you follow the previous owners recommendations in regards to leaving the choke on. The manual has nothing on experience. I leave mine on for a mile or so. "Choke" is a misnomer, there is no rich mixture here. My mechanic assured me I could leave it on all day, it's like giving it a little throttle.

Do a google search for K75 speedometer and follow links on ibmwr.org

When my speedo stops, I blow the horn three time and then it works. Sometimes I wave to imaginary friends at the same time. :p

Soon you will be telling us that it backfires down shifting in 2nd or 3rd. We know. It's ok. ;)

[Gilly]

I would suspect a wiring harness problem for the driveability concern. I did have something similar to that a number of years ago and was fixed by the dealer make improvements to the connections at the ECU (electronic control unit) under the seat, seems it was either loose or corroded a bit or both, been too long to remember exactly.
I'd avoid the bosch plugs, here again I had an experience with Bosch plugs on my bike:
Had replaced plugs, tightened like normal, next day on the way to work it started missing on a cylinder. Being somewhat mechanically inclined, I assumed there was a problem.
Pulled out the new plugs and noted a dark exhaust stain sort of between where the threads are on the plug and where the hex part is the socket fits on to. noted there was what looked like a metal seal right where the exhaust stain was and assumed compression loss at that joint, it had failed. Been using NGKs ever since with no problems.
Gilly

[BuddingGeezer]

Can't help on the speedometer, but maybe on the fan. There are basically 3 reasons the fan wont run if the fuses are good.

1. the temp probe is bad. This probe is a reducing resistance the hotter it gets ground that controls the fuel injection computer and fan switch. To check it put heat, I used a blow dryer and see that the resistance is falling. If not, could be the problem of rick running when the engine is warmed up and the fan not running.

2. The fan switch is bad. If the fan switch goes bad the temp light will not light either. The fuel injection relay fuse controls the relay energizer circuit and the horn relay fuse controls the fan itself. If the probe is good, ground a wire in the probe and hit the starter button. If the fan doesn't run, ground the other wire and hit the starter button (forget Clymer manual it's wrong). If the fan runs the switch is good, if the fan doesn't run it might also be the fan.

3. Jump the fan direct, if it runs the problem is one of the above. These fans are notorious for melting the plastic brush holders.

Usually the problem is #3, have had #2, but your rich symptoms could be #1.

Ralph Sims

[jtmckinney]

Thanks for the info. I will work on it this weekend.

Once again Thanks!
James

[godzilla]

The only time I ever use the 'choke' on my K100 is when it is really cold outside, below about 40° and only after she fires. Basically it is just to rev up the engine a bit to help warm her up. I shut it off as soon as I reach speed on the highway.

I never touch it once the temperature is about 40°.

When my speedo was doing that, I banged it a couple time to bring it back to life. However after a few years and a few hundred bangs, I ended up with a leaking seal around the glass. I washed it one day and got too much water in the speedo and that finished that deal off once and for all. Almost nothing worked on the cluster after that. I ended up replacing the whole cluster with a used one. The 'new to me' one started doing the same thing, so I had my wrench do all the published fixes and now it works 99.9% of the time.

I have often wondered how many miles she really has on her. I got her at 69K and had problems with the thing until it died at 113K. I know I had at least another 5K when it wasn't working, and we tore it apart one day and saw that someone else had already been messing with it, so that problem existed long before I bought her.

After the 85 or 86 model, BMW put a venting system on these clusters. That was supposed to help drain water out of the cluster and vent it so it wouldn't fog up. We attempted to put one of the vented backs on my cluster, but the pins were different and it wouldn't fit. He sealed the glass and put a new gasket in around the seam and used electrical tape to double seal it. Other than the Gear indicator not working and because of THAT, no Neutral switch, it works pretty good.

My Gear Indicator reads:
N: 5
1st: 5
2nd: Blank
3rd: Blank
4th: Usually 5, but when cold 4 and sometimes 9
5th: 5

Weird.

Oh, and the bulb monitor quit working.

Love them K's!

[mrich12000]

Well it's time to look for the Hall sender on Ebay or by one from www.beemerboneyard.com
this is the clasic fault of the K75 bikes and as the sender degrades it make al kinds of issues with the cdi ignition module. it shortens the dwell for the firring and makes the injector pulse go nuts. hense the rich fuel and of firring sparks.
Had a long talk regarding this with the southern BMW Ontario Guru Floyd Twiford regarding my bike as it had the same symptoms and then it died on the 401 accelorating BLAAAAAAAAAAA nice, your bike is @ 3months from that BLAAAAAA
so look for that hall unit and you will feel the diferance,I did now it pulls stumps

My 2 cents:whistle :bikes :gerg :ca