New owner of 1987 K75- with questions. - K-Bikes.com - Excellence in Motion
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post #1 of 22 (permalink) Old Nov 4th, 2006, 7:03 pm Thread Starter
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New owner of 1987 K75- with questions.

Hi everybody. I've enjoyed reading the forum today, have read all I can find about the K75.

I just bought a 1987 K75 (I think it's just the K75, no suffix on the manufacture plate or on the tail of the bike). It has only 14,000 miles from the previous (original) owner, who traded it in for a new Suzuki not too long ago, as I picked this one up at the local Suzuki dealership. Trading in my 1997 Suzuki LS650P Savage, I paid $1,500 for the Beemer. I think it was a good trade.

Questions:

(1) The bike runs slightly erratically at highway speed, mostly after warming up. The engine will surge, sometimes getting full power, then not getting full power-- misfiring is what it sounds like. It makes for a jerky ride down the highway. It seems as if there's a fuel delivery problem. I have ordered a fuel filter from the nearest BMW Motorcycles dealer, which should arrive via FedEx by Monday morning. If this doesn't fix the problem, the dealer said to look at the spark plugs and all the hoses, as the L-Jetronic injector system is supposedly very sensitive to vacuum leaks. Anybody have this problem before? Does this sound like a good plan of action, for the time being?

(2) Brakes are grabby at relatively low speeds. I notice it mostly as I come to a slow stop at stoplights in town. It feels like a thick spot in the disc or a rear drum out of round (yes the bike is drum rear brake), as you come to a stop it's sorta the inverse of the engine surges. The brakes get strong in one spot each rotation, or at least that's how it feels. I plan to change the brake fluid and see if that cures it. Would old fluid mess with the ABS and cause such a feeling? Is this natural for the older K bikes? Should I check the discs up front to see if one's out of round or something? I would think the surge would be extra-noticable at highway speed if there was a disc out of whack.

(3) Oil capacity: Four quarts? The owner's manual supplied was from a K100, not a K75. I have read elsewhere that it's four quarts, but questioned the reliability of the site.

(4) Idle speed is a bit low (showing around 900 RPM). Could this be a result of a dirty fuel filter? If not, how do I adjust it?

This BMW is my second bike, after spending a couple years on "Zook," my customized Suzuki single cylinder. I had been keeping an eye peeled for an F650, in keeping with single-cylinder theme, but couldn't pass up the deal on this K75. I think, if I can get it running smoothly again, I won't regret the purchase. The previous owner was an older gentleman who only took it on a handful of longer rides each year, while the rest of the time it stayed parked in his barn. He was a regular customer of the local shop where I bought the bike, buying a new battery about once a year because he didn't have a place in the barn for a battery tender.

Thanks for reading, and looking forward to the experience of owning a BMW cycle,
Banger
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post #2 of 22 (permalink) Old Nov 4th, 2006, 10:12 pm
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I had a 87 k75 for six years, great bike but fell in love with a 02 1200rs this summer. My k75 started running erratic, then really bad, turned out to be the rubber flex hose past the Jetronic. One small pinhole it runs rough, then the big hole- it hardly runs. Enjoy this bike, it is the smoothest engine you will ever have.
Carl
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post #3 of 22 (permalink) Old Nov 6th, 2006, 5:11 pm
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Dear Banger: Sounds like you may have fouled spark plugs, cracked ignition wire insulation or fouled injectors from sitting too long. If the bike has high milage, it could be the fuel pump not being able to produce the required pressure at the injectors?

Also, please be advised that I have an original K75 Owners (Riders) manual that I really need to trade to you for your K100 manual! I just bought a 1987 K100LT and really need to buy (or borrow to photocopy) a manual! The manual I have covers the K75c and K75s models and it is copywrited 1990. This is a BMW original and is a good one with all the pages and the fold out electrical diagrams. Thank you very much.- sherrill
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post #4 of 22 (permalink) Old Nov 6th, 2006, 8:42 pm
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No ABS

If it's indeed an '87, and it has a rear drum brake, then it doesn't have ABS. Those appeared around '91 or '92, and only with disk brakes front and rear. I sounds to me like you could stand getting the drum turned, and getting new brake shoes. What you describe could be done by the shoes resting against the drum and corroding, causing a grab every time the shoe passes that point in braking.

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post #5 of 22 (permalink) Old Nov 7th, 2006, 9:40 am
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Cool

If your K75 looks similar to this, you've got a 87 as I do. It should have a rear drum brake.



the irratic surging and low idle maybe the same issue, fuel pump or fuel line maybe clogged, run the bike with at least one tankful of freash fuel before you rip into the fuel pump. Keep the engine rev above 4500 rpm when you're traveling at highway speed.
When was the last time the valve clearances were checked? they usually hold adjustment pretty well, but 14000mi. in 20 years, that bike problably have not been checked for a while.

Rear drum brake rarely goes out of round, it does not generate enough friction do to any significant braking force. I didn't know the 87 K74 come with ABS...

When I change the oil, I always keep track of how much oil is drained and put back in roughly the same amount, start the engine, warm it up to running temp and shut of the bike to check the oil lever and add more that way until the oil lever is within the red circle of the sight window. I never really keep track of total oil capacity.

Good luck, keep posted on your progress.

Master your environment, and you will survive just fine.
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post #6 of 22 (permalink) Old Nov 7th, 2006, 10:15 am
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Oil Capacity

The manual says 3.7 quarts without a filter change, and 4.0 quarts with a filter change. Which begs the question, who changes their oil without changing the filter? It always seemed like leaving the dirtiest stuff in the motor to me, when the whole point of the exercise is to get the damn dirt out of there.

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post #7 of 22 (permalink) Old Nov 7th, 2006, 12:56 pm Thread Starter
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Quote:
Originally Posted by wastedspark
Dear Banger: Sounds like you may have fouled spark plugs, cracked ignition wire insulation or fouled injectors from sitting too long. If the bike has high milage, it could be the fuel pump not being able to produce the required pressure at the injectors?

Also, please be advised that I have an original K75 Owners (Riders) manual that I really need to trade to you for your K100 manual! I just bought a 1987 K100LT and really need to buy (or borrow to photocopy) a manual! The manual I have covers the K75c and K75s models and it is copywrited 1990. This is a BMW original and is a good one with all the pages and the fold out electrical diagrams. Thank you very much.- sherrill
Wastedspark: Spark plugs are forthcoming if the fuel filter doesn't solve the problem. The bike has only 14,000 miles on it-- exceptionally low for its age-- and the fuel pump sounds like it's pumping away, emitting a whirr upon switching the ignition "on." I even noticed the pump still running one night when I stalled the bike while pulling into the basement. So I don't think the pump's the problem.

And a trade of manuals sounds like a good ideer. PM me with pix if you will.

Rob: Your brake diagnosis sounds probable. I'll look into it this weekend when we give the bike a good once-over. I only assumed it had ABS because there's a small line running down into the top of the drum that looks like an ABS sensor wire.

The "initial" service this weekend will entail a change of oil and oil filter, change of fuel filter, change of brake fluid, spray-down of brake parts with brake parts cleaner, check of all hoses, check of spark plugs, and if possible, a check of the valve clearances.

Thanks for the help so far. Keep the suggestions coming.

Regards,
Banger
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post #8 of 22 (permalink) Old Nov 13th, 2006, 12:49 pm Thread Starter
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An Update, post-service:

Hey, thought I'd drop a line in updating after our "initial service" of the new member of the family.

Got into the fuel tank and found that the filter (a Purolator, though it at least had the BMW symbol on it) was very stopped up. You couldn't blow air through it. Furthermore, there was a tear in one of the hoses coming off the fuel pump. Luckily that tear was near the end of the hose, so I cut an inch or so off of it and replaced it. It still reached its destination tube fine, it was just a little shorter. The new fuel filter was inserted-- this time, a BMW original part instead of the Purolator-- and all seemed to go off without a hitch. I must note, though, there was some gunk in the tank from the foam rubber that seals the fuel pump off from the rest of the tank. It has rotted severely. Can this piece be replaced by itself? I pulled the fuel pump and noted that it is removable from the actual pump element, as is the screen filter on the other side of the pump. The screen, it should be noted, was very clean.

Those relatively minor changes seemed to make the erratic running go away, though I've only ridden it about 45 miles since then. Will update again if it rears its head once more.

The brake fluid was changed. The old fluid was a dark, almost chocolate brown color. Yuck. Drained and replaced with a vacuum style bleeder, so that you don't have to do it the old fashioned way. New fluid is a light honey color. The brakes are stronger and a bit smoother, but the grabbiness is still apparent at low speed. Might need to take off the caliper/pad housing, remove the pads and spray the calipers to ensure there's no gunk there that the brake parts cleaner missed.

Spark plugs were checked. They were NGKs, but at least the gaps were right. Didn't seem too bad. A little dark in color, but my step-father ran the wire brush over them on the bench grinder and they came back shiny as new. Will be replacing these with BMW-recommended Bosch before the spring comes and I actually get the chance to ride more than once or twice a month.

The oil change went relatively smoothly. That drain plug lets the old oil out all at once! On the old filter, the previous owner had inscribed the last date the oil was changed (September 2004) and the mileage (13,500), so it had only had 1,000 miles put on it in two years! That really seals it as to why this K needed the cobwebs dusted off real good before doing any serious commuting. I put the recommended 20w50 into it and replaced the old filter (a BMW original-- but why, when everything else we found was NOT as recommended by BMW?) with a Fram, and it seems happy now. Runs like a top so far. I plan on getting a BMW filter next time, so long as it's not exponentially higher in cost.

Thanks for your help so far. Suggestions for the brakes?

Regards,
Banger
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post #9 of 22 (permalink) Old Nov 13th, 2006, 7:54 pm
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manual for a K100

I too need and will happily pay for a copy of a manual for an 85 K100. Even copies of a manual.

Let me know how! :o

"What follows is based on actual occurrences. Although much has been changed for rhetorical purposes, it must be regarded in its essence as fact. However, it should in no way be associated with that great body of factual information relating to orthodox Zen Buddhist practice. It's not very factual on motorcycles, either."

Robert Persig - Zen and the Art of Motorcycle Maintenance


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2000 323i (Sold)
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post #10 of 22 (permalink) Old Nov 13th, 2006, 8:52 pm
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Banger
Great that you got a lot of the maintainance cleaned up.
There is nothing wrong with just using NGK plugs.
tip: Check the ohm reading of the plug wires. They should be around 7,500ohms. The main thing is if there is one wire that is way out of range with the other plug wires. There are expensive(around $55.00 EACH).
The main reason for using OEM oil filters is because they are unpainted and mounted internally! Did that Fram filter you put in have paint or that black gripper stuff on it? It might flake off and plug up the oil pickup screen or worse. Order filters in bulk from ChicagoBMW. Get your part numbers from www.maxbmwmotorcycles.com parts fiche.

Beemer01
You can pick up a Haynes 2-valve K-100, K-75 repair manual at just about any BMW dealer in the country for under $25.00.

Bruce C
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