Why you want to change the fuel filter on a '86 K75 bike

[gawga_boy]

While lubing the splines this weekend I took the opportunity to do some other maintenance work which included changing the fuel filter. First thing I found was the outlet hose was cracked and had some of the outer rubber flaking off. I also noticed black stuff through the inlet tube on the filter. After I put everything back together I fired my K75 up and noticed it was running slightly smoother at idle. That, along with the black junk in the inlet tube, prompted me to cut open the old fuel filter to see what was inside.

Here's what I found.









The brown red stuff in the can on the last photo is powdered rust.

Yesterday I went on a 130 mile road test. Not only is the engine smoother with less vibration at all speeds but it had better throttle response especially in 5th gear in 55mph to 85mph acceleration when passing slow pokes. I'm not an expert but I suspect that filter was clogged enough to give a somewhat erratic and less than optimal fuel pressure to the injectors that resulted in a slight imbalance in the cylinder combustion.

I don't know when the filter was ever changed but it was a BMW logo stamped Purolator PFC-39 filter.

Sorry for the out of focus images as the only digital camera I have is in my cell phone and it doesn't do so well on close ups. But you'll get the general idea of how bad the filter was.

[sleeper]

Looking at these pictures and following along with my buzz-dilemma, I am wondering what the practical interval is for changing the K75 fuel filter. I had it done by a dealer when I got my bike last August with 34,000 miles on it. I've got 45,000 miles now (yeah, it's been fun to ride) and planned on a fuel filter change at 54,000. Is 20,000 miles too long of an interval?

[Bobmws]

Looking at these pictures and following along with my buzz-dilemma, I am wondering what the practical interval is for changing the K75 fuel filter. I had it done by a dealer when I got my bike last August with 34,000 miles on it. I've got 45,000 miles now (yeah, it's been fun to ride) and planned on a fuel filter change at 54,000. Is 20,000 miles too long of an interval?

No real mileage figure for a fuel filter, it only takes one bad tank of gas to mess it up. Looking at Gawga boys filter I'd say it either had been in service a long time for the hose to degrade, or someone had use non-submersion rated hose.

[gawga_boy]

According the my factory repair manual the fuel change interval is 15,000 km and 30,000 km (9322 mi & 18645 mi). 15,000 km "When fuel quality is poor". I think my fuel filter's problem was it was never changed and original to the bike or hadn't been changed in a very very long time. I would suspect that the 20,000 mile interval is fine but Paul and others here have more experience than I have with the K bikes. Hopefully they will weight in shortly.

[Zagando]

Even a new filter can soon become clogged by one bad batch of gas; it's best to always carry a spare just in case. I would change them at least once a year otherwise.

Napa carries an inexpensive replacement that works for me and a lot of other folks---search here or IBMWR for the model number (3032 IIRC?) to be sure.

There seems to be a minor controversy whether or not these generic filters will withstand the fuel injection system pressure but so far so good for me and those that use them. Maybe an OEM on hand wouldn't hurt if cost isn't a big deal.

[gawga_boy]

someone had use non-submersion rated hose.

It appeared to be the standard BMW fuel hose. So I'm betting the filter had been there a very very long time.

[mieczkow]

Yeah, I changed everything rubber and "attackable by fuel" on my 87 K75S last year. It just seems after years of constant soaking in gasoline anthing except metal itself deteriorates. I pulled everything out and did a wholesale replacement of filter, strainer, rubber "bib", the sealing ring on the filler cap, etc. I found all the old rubber material to be both deteriorated and crumbly. It's not too difficult to do, although some of the parts will shock you with their cost. I've never had a fuel problem and the interior of the tank looks really clean by visual inspection.

[PHMARVIN]

Hi, Gawga_Boy,
I think the filter you changed was probably the original filter. I have only seen one BMW motorcycle fuel filter with the Purolator number stamped into it (the filter is in my parts stash) and I know that filter is at least 20+ years old. I don't think BMW has sold or used these filters for a very long time.

Check the black rubber vibration damper, the one the fuel pump sits in. If it is soft and gooey, change it - NOW! If it disintegrates and the fuel pump ingests it, you'll be buying a new fuel pump!

[gawga_boy]

Check the black rubber vibration damper, the one the fuel pump sits in. If it is soft and gooey, change it - NOW! If it disintegrates and the fuel pump ingests it, you'll be buying a new fuel pump!

Hey Phil,

I'm not surprised that it's the original filter. Lots of stuff on the bike was original including lots of bolts with what appears to be factory paint bolt removal indicator marks.

Appreciate the heads up. I was gonna do just that as well as check and replace all those fuel hoses if needed.

Frank

[gawga_boy]

black rubber vibration damper

Those thangs ain't cheap. But not as expensive as a new fuel pump.

[barooo]

Your post inspired me to change mine over the weekend. I've been meaning to, I bought a new filter last year but was never arsed to bother. I noticed that my fuel pump whine is pretty darn loud, so I finally got around to it. I also needed to change my gaskets in the cap, I did it last year but only the ones that were visibly deteriorated, not the one under the whole assy or the one that you have to snap apart the locking mechanism to get to since they both looked okay (nor the metal washer/ring thingy, nor the o-ring underneath). This time around my leaking with a full tank on hard stop/start or when parking on the sidestand is seemingly gone.

My bike starts easier now, it usually takes 6-8 cranks and a good 2-3 seconds when cold, now it seems like it's 2-3 cranks and about a second. Idles better too, especially cold, and the throttle response seems better. Nice. And it may be my imagination, but the fuel pump whine is much less pronounced. Hell, it even seems to shift easier

The old one I'm hanging on to as an emergency backup, but I may just buy a new one and throw in the trunk, now that I've seen the difference. not sure when it was last changed; possibly along with the splines, and misc. that buddingGeezer did before he sold it to the PO but the records I have are ambiguous about the fuel filter. And even if he did, 2.5 years is probably enough to warrant a new one.

next up, I noticed that the vibration seat thingy under the fuel pump feels slightly sticky. No visible deterioriation, but it's on the list for this winter along with rotors (and pads). I also ordered the air accumulator funnel thingy so I can eliminate my vent into the crankcase which is still stock.

[PHMARVIN]

Those thangs ain't cheap. But not as expensive as a new fuel pump.

Hi, Frank,
Yes, they are NOT cheap!! And since you have an '86, it uses the 52mm pump and the damper for it is more expensive than the one for the later 43mm pump. I am slowly trying to bring an '85 K100RT back to life and the damper is almost a thick liquid, as well as the pump being rusted. I bought a used pump off of fleabay and, when it arrived, it was still mounted in the vibration damper and the clip to clip it to the tank! So for $81, I got a working pump, damper and clip! As for less expensive parts, check out the MotoBins website. They are in UK, the prices are in British Pounds, and shipping can be expensive, but all-in-all, delivered to my door, the prices are usually less than even Chicago BMW and in all cases, delivery has been MUCH quicker than Chicago BMW.

[gawga_boy]

barooo........ glad I could be of service.

Phil.... thinks for the headup on fleabay (wife just loves when I'm on a fleabay roll ) and the motobins site.

BTW: in addition to having a bmw logo stamp on my filter it also has 1 460 453 with the inlet and outlet marked EIN and AUS respectively.