Good afternoon!  I purchased a 1985 BMW K75 back in April.  Parked it in my driveway until I could get my endorsement straightened out, and we got hit with a massive sleet storm later that week.  The storm knocked the bike over in the middle of the night and blew the cover off in such a way that it was covered with sloppy frozen precipitation the next morning.  It has not started since.  I should note that I am a novice in all things mechanical.  I've maintained my own vehicles for years, but only through knowledge gleaned from YouTube and various forums, so there are definite gaps in my understanding and capability.

Crank


The first issue was extremely inconsistent results when attempting to start the bike.  Following the start up procedures initially produced regular cranking of the starter but not starting, but after several attempts while fiddling with the choke and throttle, the starter would crank even after the starter button was released.  I could stop it by turning the key to the off position.  Additional attempts got even weirder.  Once it stopped starting when the button was released, but then started cranking again when I released the clutch.  I again was forced to turn the key to get the starter to stop.  A quick search of the forum indicated a welded starter relay.  I replaced the component with a Niche starter relay and the bike went back to cranking as it should following start up procedures.  As far as I can tell, there are no additional issues with the starter, but the bike still won't start.

Fuel

After noticing no fuel pump noise, I pulled the fuel line to check the pressure.  Stabbing the starter elicited only a dribble of fuel.  Before I replaced the pump and filter, I replaced the obviously deteriorated fuel pump connector under the seat with a nice Deutsch connector.  I still didn't have fuel pump noise, so I replaced the fuel pump and filter.  This gave me a nice robust whir when I stabbed the starter and corresponding pressure in the line going into the injector rail.  I also pulled the injector rail with all the injectors still attached and ensured I had good spray when the starter was pressed.  This seems to indicate to me that I have good fuel flow and at least no interference from the EFI, but the bike still won't start.

Spark

I also pulled all the plugs and although they weren't pristine I had spark from all of them when I grounded them and stabbed the starter.  I replaced them anyhow because plugs are cheap.  I forgot to mark the cables and take a picture of the routing, but some quick research got everything back where it was before I touched it.  I also sprayed ether directly into the cylinder while I had a plug out and didn't get a single combustion.  As far as I can tell, I have good spark but the bike still won't start.

Air Flow


I pulled the air box apart to check the filter and the filter was also pristine.  The bike wasn't purchased in a very dusty environment so this didn't surprise me.  Spraying ether directly into the air conduit with the air box disassembled produced no combustion.  I had a friend crank the bike with my hand over the exhaust and I got intermittent pressure from the cylinders moving, so it would seem to me that I have good air flow but the bike still won't start.

Miscellaneous


All of the fuses in the box on the left hand side of the bike seem to be intact.  I have the bike on the center stand not the kick stand.  The transmission is in neutral and the clutch is in.  I put fresh gas in it and even if I didn't the ether should have at least ignited.

I'm not really sure where to go next.  I'd appreciate any guidance on this.  Thank you all so much for your time.

Welcome, the Upper Peninsula Is a great place to ride.  I've been through there 4 times now, I even almost got a deer with my K75RT on Highway 28. 

Have you looked inside the tank?  Often these old beasts will have a lot of dirt and dissolved fuel pump vibration damper in there, and when the bike fell over all that crap may have been disturbed and then was able to clog the screen to the fuel pump. 

As a result, some of us when getting a "new" Brick will remove the tank and do a good flush and inspection of the inner working bits.  Depending on how filthy the insides are, a couple gallons of white vinegar left to soak followed by a scrub with a Scotchbrite pad will get the worst out.  Then, the wise owner will replace the fuel filter and the hoses in the tank with new.  The best filter is the NAPA 3032 and the fuel lines should be for submerged use in ethanol fuel which I think is the SAE J10 rating.  The pump and the mounting parts are a judgement call based on how they look and whether the pump will spin when power is applied.  Be very careful around the fuel level sender, they are fragile and harder to find than unicorn poop(not to mention $$$$ when you do find one).

Good luck with getting it running.  They're great bikes.

Point-Seven-five wrote:Welcome, the Upper Peninsula Is a great place to ride.  I've been through there 4 times now, I even almost got a deer with my K75RT on Highway 28. 

Have you looked inside the tank?  Often these old beasts will have a lot of dirt and dissolved fuel pump vibration damper in there, and when the bike fell over all that crap may have been disturbed and then was able to clog the screen to the fuel pump. 

As a result, some of us when getting a "new" Brick will remove the tank and do a good flush and inspection of the inner working bits.  Depending on how filthy the insides are, a couple gallons of white vinegar left to soak followed by a scrub with a Scotchbrite pad will get the worst out.  Then, the wise owner will replace the fuel filter and the hoses in the tank with new.  The best filter is the NAPA 3032 and the fuel lines should be for submerged use in ethanol fuel which I think is the SAE J10 rating.  The pump and the mounting parts are a judgement call based on how they look and whether the pump will spin when power is applied.  Be very careful around the fuel level sender, they are fragile and harder to find than unicorn poop(not to mention $$$$ when you do find one).

Good luck with getting it running.  They're great bikes.

I did check the screen when I replaced the pump and filter and it was clean.  There is some detritus in the bottom of the tank, but I was able to remove a lot of it by hand and with a siphon.  Regardless, if the pump is pressurizing the line and I have good fuel spray, doesn't that mean that everything upstream of that should be good?

How's the battery doing? Sometimes these bikes will seem to crank okay, but the battery isn't quite strong enough to fire it into life.
I'd jump the battery from a nearby car if you can and have another go - it'll eliminate one potential fault.

Just want to confirm, you said bike is in neutral. Does that mean green light too?

Fuel, spark and air are allegedly present despite a likely less-than-gentle impact of the Brick upon the ground, and a sleet bath. Verify that, starting from the left, cylinder #1 is connected to the leftmost coil, cylinder #2 is connected to the middle coil and cylinder #3 is connected to the rightmost coil.

A description of spark plug condition more apt than weren't pristine would be wet or dry, especially when describing the replacements for this occasion. I will point out that because they have been allegedly firing, the spark plugs can never legitimately be described as pristine in the future; however, they once were pristine but those days are gone.  

Crank the engine a few times, remove all three spark plugs and tell us whether the plug tips are wet or dry. If they are wet, check the fuel pressure with a pressure gauge attached by a t-fitting to the delivery line that is fitted to the injector rail. I'm betting they are wet, but since I really have nothing at stake, if I'm mistaken I pledge to slap the knuckles of my left hand once briskly using a folding rule marked in both inches and millimeters used for measuring animal tracks and scat.

The engine might be flooded and the combustion chamber oil soaked. Maybe just removing the plugs and cranking the engine will dry it out if that is the case. A hard fall like that could conceivably mess with the timing chain but that is for later.

which side did the bike lye on all night ?

Follow what Laitch said to do and report on the wet dry plugs,

if you have a pressure gauge you might want to verify that there is sufficient compression pressure in each cylinder.  

Don't know that it would be related to a fall, but stuck piston rings or valves would create a no-start.  It's easy to pull the valve cover and inspect all that too.

if the bike lies on the left hand side all night and you pick it up and try to crank it you may break a ring bend a valve etc  , just a thought so try a compression test

Sorry for your trouble. Try this: give each cylinder a squirt of engine oil to increase compression. Chris Harris has a video about this no start due to lack of compression.