Fuel Starvation Issue or what? '87 K75s

kentuvman · Sep 27, 2015

Mileage @ 54,000

ON way home from Billings rally my K75s was acting up - the idle was below normal and sometimes it would die. It seemed like there was a dead spot on the first 1/3 of the power band but above 5k bike ran normal. Another way of saying this would be as if the choke were on and the engine was running rich until getting to higher rpm.

Replaced Fuel Filter when I returned home and that seemed to help.

Went on a camping trip this weekend and before leaving, I added @ 8oz if the Chevron Techron Fuel Treatment with a full tank of gas. As my ride progressed, the bike seemed to run better and was idling like normal @ 1k rpm.

Yesterday, we went on a scenic ride and as we were leaving a town my bike completely shut off - it was like a turn of a switch! I tried restarting but the engine just cranked but no go. My initial thought was a failed hall sensor, failed fuel pump, or the computer conked out. My friend stayed behind and we started troubleshooting - checked the fuse to the fuel pump with a multimeter, checked the power going to the fuel pump, pulled off a plug and confirmed there was a spark. Knowing we had a spark, focused on confirming if the fuel pump was working. Because we were parked on a main street in the midst of Apple days, I couldn't hear if the fuel pump was activating - finally, I pulled off the filler cap, pushed the flapper down and touched the starter button with my ear close to the opening in the tank - I barely pushed the starter and heard the fuel pump - I pushed it a couple times and then tried to start the bike and she coughed but started and the incident did not repeat itself.

This morning on my ride home from Wisconsin @ 160 miles, the idle got rough again when I stopped for gas - at a stop sign, the motor died because the idle was stumbling - before leaving, I added the remaining 8ozs of the Techron and problem seemed to clear up.

Any ideas of where to check or some knowledge of what's going on? I did notice some seepage around the front injector but it's not leaking or wet but may have seeped at one time and a few times I've noticed a fuel smell when the bike is running but it's not leaking.

Would like to get this resolved before taking another road trip!

Thanks!

Ken

pglaves · Sep 27, 2015

kentuvman said:
Mileage @ 54,000

ON way home from Billings rally my K75s was acting up - the idle was below normal and sometimes it would die. It seemed like there was a dead spot on the first 1/3 of the power band but above 5k bike ran normal. Another way of saying this would be as if the choke were on and the engine was running rich until getting to higher rpm.

Replaced Fuel Filter when I returned home and that seemed to help.

Went on a camping trip this weekend and before leaving, I added @ 8oz if the Chevron Techron Fuel Treatment with a full tank of gas. As my ride progressed, the bike seemed to run better and was idling like normal @ 1k rpm.

Yesterday, we went on a scenic ride and as we were leaving a town my bike completely shut off - it was like a turn of a switch! I tried restarting but the engine just cranked but no go. My initial thought was a failed hall sensor, failed fuel pump, or the computer conked out. My friend stayed behind and we started troubleshooting - checked the fuse to the fuel pump with a multimeter, checked the power going to the fuel pump, pulled off a plug and confirmed there was a spark. Knowing we had a spark, focused on confirming if the fuel pump was working. Because we were parked on a main street in the midst of Apple days, I couldn't hear if the fuel pump was activating - finally, I pulled off the filler cap, pushed the flapper down and touched the starter button with my ear close to the opening in the tank - I barely pushed the starter and heard the fuel pump - I pushed it a couple times and then tried to start the bike and she coughed but started and the incident did not repeat itself.

This morning on my ride home from Wisconsin @ 160 miles, the idle got rough again when I stopped for gas - at a stop sign, the motor died because the idle was stumbling - before leaving, I added the remaining 8ozs of the Techron and problem seemed to clear up.

Any ideas of where to check or some knowledge of what's going on? I did notice some seepage around the front injector but it's not leaking or wet but may have seeped at one time and a few times I've noticed a fuel smell when the bike is running but it's not leaking.

Would like to get this resolved before taking another road trip!

Thanks!

Ken

The last two times the problem happened it cleared up when you opened the fuel tank filler cap. This strongly suggests fuel flow problems due to a clogged fuel tank vent. This is common with clogged vents on carbureted Airheads and not so much so on fuel injected bikes. Nonetheless, that is my best hunch.

kentuvman · Sep 27, 2015

Only thing different is I'm using a Cortech tank bag that covers the fuel cap with the big piece of thin foam that sits beneath the tank bag but don't think that's it - will check the vents.

If a clogged vent, why would motor run smooth above 5k rpm?

tinytrains · Sep 27, 2015

A couple thoughts. The low speed problems could be cracked crank case breather hose. This lets air in after the flow meter causing a lean mixture at low speeds. These hoses all need replaced after 20 years (easy to do). The problem I had with sudden shut-off was the electrical pass-though on the bottom of the tank. When it got hot, the connection to the pump would open and the bike would stop. $200 for a new float assembly fixed that.

Next time it does not start, pull the rear hose off the fuel rail and hit the starter button. It should squirt like a garden hose. If not. the pump is not running.

Good luck.

kentuvman · Sep 27, 2015

tinytrains said:
A couple thoughts. The low speed problems could be cracked crank case breather hose. This lets air in after the flow meter causing a lean mixture at low speeds. These hoses all need replaced after 20 years (easy to do). The problem I had with sudden shut-off was the electrical pass-though on the bottom of the tank. When it got hot, the connection to the pump would open and the bike would stop. $200 for a new float assembly fixed that.

Next time it does not start, pull the rear hose off the fuel rail and hit the starter button. It should squirt like a garden hose. If not. the pump is not running.

Good luck.

thank you - thats the only hose I've not replaced - also need to replace fuel tank vent hoses - looked up p/n on Real OEM and not seeing aft fuel rail hose and the two vent hoses - should the local BMW dealer carry them if I bring the existing hose in? I don't think most auto parts sell them. Thanks again.

tinytrains · Sep 28, 2015

The crank case breather hose is a special molded part you can only get from the dealer. Good news it is only 16 bucks.

Scott

kentuvman · Sep 29, 2015

Update - Fuel System Getting Needed Attention and Air Box too!

Following my hunch, I associated the smell of gas and the dried debris around the front injector as a potential contributor to my stumbling idle and bogging at low rpms. Removed the fuel tank today and discovered the following:

1. Before removing the injectors, used compressed air to blow away debris around the injectors. All are dirty but front injector is especially dirty and probably was leaking.
2. Planning to renew the aft hose that attaches to fuel rail, removed air cleaner top and found a mouse had made it's home in there - I hadn't been in there in 2-3 riding seasons.
3. The (3) rubber manifolds may be in good shape but they're filthy and will be replaced.
4. The fuel overflow hose is old and brittle and will be replaced.
5. Will run some weedwacker line through the vent passages to ensure they are clear.
5. The mini-filter on the other vent hose - do these wear out? It is very constricted. Was planning to replace it and the hose as well.

Spoke to Mr. Injector today in Idaho and planning to ship mine for service.

My objective is probably like many of you reading this - to know my ride as much as possible and try to avoid a breakdown - when she died in Wisconsin this weekend it was pretty unsettling. I felt very humble when she fired up and got me home - still the K75 is probably one of the most reliable models ever produced by BMW but they all need maintaining.

I'll continue to post progress when I get my parts - probably will make an order with Motobins.

Thanks for your help so far!

AntonLargiader · Sep 29, 2015

It's not a mini filter... if it's what I think you refer to, it's a one-way valve going from the tank into the front of the crankcase. Bikes without the SHED system will not have this, so you could just cap it off at the crankcase to see if it makes a difference.

kentuvman · Sep 29, 2015

Thanks for your feedback Anton - below is a picture of what I describe as a filter.

AntonLargiader · Sep 29, 2015

That's what I thought.

roncooper · Sep 29, 2015

kentuvman said:
Thanks for your feedback Anton - below is a picture of what I describe as a filter.

It is a one way check valve that some have used as a brake bleeder.

pglaves · Sep 30, 2015

In 1986 when I bought my K75T it had that valve in the vent line between the tank and the stub atop the engine case. It was originally intended to vent the fuel tank to the crankcase but not allow blowback from the crankcase. The dealer disconnected the line, rerouted the vent hose, and capped the crankcase stub at the 600 mile service. There had already been cases of full fuel tanks, sitting in the hot sun, venting raw fuel into the crankcase. Oil diluted with gasoline is not kind to bearings and such.

58058D · Sep 30, 2015

Wow, I was surprised to read that there are still some bikes out there that still have this one way valve attached, and presumably still venting into the crank. And if it was still attached but not connected to the crank case, perhaps it is plugged and could be part of the venting issue. I seem to recall they were a 10 psi valve? I know mine would squeal when the vapors were trying to pass through it. Asking around about this squeal back in '91 with 4,000 miles on a new to me K100RS is how I learned about removing this and extending the vent hose out like the factory later did......I think I simply put a good sized screw into the short tube still attached to the block.

kentuvman · Sep 30, 2015

58058D said:
Wow, I was surprised to read that there are still some bikes out there that still have this one way valve attached, and presumably still venting into the crank. And if it was still attached but not connected to the crank case, perhaps it is plugged and could be part of the venting issue. I seem to recall they were a 10 psi valve? I know mine would squeal when the vapors were trying to pass through it. Asking around about this squeal back in '91 with 4,000 miles on a new to me K100RS is how I learned about removing this and extending the vent hose out like the factory later did......I think I simply put a good sized screw into the short tube still attached to the block.

It was never plugged into anything other than the vent on the underside of the tank - seems to always have run fine - go figure.

kentuvman · Sep 30, 2015

Update for today

1. Injectors shipped off to the Injection Doctor for repair / renewal.
2. Airbox removed and debris removed
3. Airfilter, although old, looks perfect - used compressed air with a needle type attachment and cleaned out every groove or fold - I can't see the point in buying a new air filter - am I missing something? No oil, discoloration - looks really good - it's a Purolator AF-3389
4. Ordered needed Manifold parts and clamps and fuel vent overflow hose from local BMW dealer - compared to Motobins, I believe I'm saving dollars - all parts @ $185 including tax and delivery to their location. Told manager I'm an MOA member and she went way above and beyond to give me a break on cost. Parts should be in early next week.

Thanks to Lee Fulton for confirming the part numbers in a previous email. Lee had mentioned Summit Racing carrying the correct Oetiker clamp pliers - is the the one I need? http://www.summitracing.com/parts/wmr-w83013/overview/
I noticed online that these pliers have different configurations on the pliers portion that secures the oetiker clamp.

Took a picture of where I'm at - read the steps in my Clymer book and will re-read several times before tackling the R&R of throttle manifolds -if anyone knows of any short cuts, words of wisdom please share what you know. Wondering how to remove the Oetiker clamps and use the tool to reinstall - I'll do my homework too!

Making progress - learning along the way!

kentuvman · Sep 30, 2015

PGlaves said:
In 1986 when I bought my K75T it had that valve in the vent line between the tank and the stub atop the engine case. It was originally intended to vent the fuel tank to the crankcase but not allow blowback from the crankcase. The dealer disconnected the line, rerouted the vent hose, and capped the crankcase stub at the 600 mile service. There had already been cases of full fuel tanks, sitting in the hot sun, venting raw fuel into the crankcase. Oil diluted with gasoline is not kind to bearings and such.

Always wondered what the black stub was - looks like mine's capped off too - I guess PO or dealer never removed the "filter" or whatever it's called.

kentuvman · Oct 2, 2015

Yesterday's progress

Found a capped hose going into crankcase after removing air box - cleaning while waiting for parts.

72bavaria · Oct 2, 2015

I just experienced the same symptoms as you. Engine seemed to be struggling for fuel. My mechanic did all the diagnostics you mentioned above. Problem was in the ignition wiring and connector was replaced near or at the ignition control under the fuel tank.

58058D · Oct 3, 2015

Ken, glad to see the line going into the crank case was capped off. That is what we all did back then, as Paul noted. If the pressure valve on the line from the tank vent is working properly, any time the pressure in the venting system gets high enough, fuel can come out and drip where you don't want it to. So, many of us removed the pressure valve and extended the line down and out near the swing arm, etc, like the 'newer' bikes. While fuel in the oil is no good, fuel dripping on a hot engine is also a recipe for disaster.....

kentuvman · Oct 6, 2015

58058D said:
Ken, glad to see the line going into the crank case was capped off. That is what we all did back then, as Paul noted. If the pressure valve on the line from the tank vent is working properly, any time the pressure in the venting system gets high enough, fuel can come out and drip where you don't want it to. So, many of us removed the pressure valve and extended the line down and out near the swing arm, etc, like the 'newer' bikes. While fuel in the oil is no good, fuel dripping on a hot engine is also a recipe for disaster.....

Thanks for your reply! Can the hose that's capped off be shortened so it is closer to the crankcase?

Another question - since things are apart, should I replace the rubber hose inside the spring that connects to the fuel pressure reg. and fuel rail - why is the hose inside a spring?

Fuel Starvation Issue or what? '87 K75s

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