K75 starts but will not run

[FranK75]

My ’91 K75 starts but will not run. It starts and idles for maybe 1 second and dies. Occasionally I can get it to rev if I give it some throttle but I get frequent backfires through the air box and it will not run at idle. I took it to the Beemer dealer in Charleston last spring when it was doing the same thing. They said I had bad fuel and water in my fuel. They cleaned that up and it ran great for a few months last summer. This spring – forget about it! Here is what I’ve done so far:

•   Checked Compression – All cyls are good ~ 120
•   Removed and cleaned out gas tank – what are those crystals that form in there?
•   Installed a new fuel pump & filter – pressure from pump is 90 psi
•   Fuel pressure at rail is 40 – it does not go up to 60 psi on starting
•   Spark is good
•   Injectors are injecting
•   Fresh spark plugs
•   Removed airbox and cleaned temp and mass air sensors
•   Cleaned and retightened battery ground

Bike has been mostly garaged and I don’t see much if any corrosion on electrical. I think my FI computer is good (not really sure how to test it). Aside from installing a new fuel pressure sensor I am baffled. Any advice is welcomed.

[Bfbob]

Just in case you haven't found the answer in the last 7 months...  sounds like you've checked the easy stuff except one:  Firing order. Too obvious?  Maybe - with a triple, if one is wrong, two are wrong and you've only got one cylinder firing.  Easy to check

Next thing isn't so easy.  Check the cam chain - maybe it's jumped a tooth, or is just way stretched.

Good luck!