haunted fuel injector

[goodworkmax]

I have a '90 K75.  the fuel pump quit last summer so I had a rebuilt put in by Duncan's Beemers in Maynard MA.  Bike drove great after that until I was 2/3 of the way to Saratoga Springs and all of a sudden one of the cylinders quit.  I took the rail off the bike, cleaned out the injectors and the bike ran great again. (Better in fact than when I bought it 2 years ago).  Then yesterday I was taking my first long ride since doing the work and the same (rear) cylinder quit again.  This morning I pulled the rail again and leaving the injectors on cranked the bike and let them shoot onto a piece of cardboard.  It was obvious that the rear injector had a compromised spray pattern and lower volume.  I pulled that injector, cleaned it with some techron and reinstalled.  Tested the spray patern again as above and all 3 looked good.  put it all back together and the Bike ran great for about 12 miles of my commute to work and then the cylinder quit again. 
Would like some opinions as to whether the injector is bad or is it just collecting debris at the end of the rail?  Should I replace or put an inline filter in the fuel line coming into the rail?   

[BrickMW]

I would swap it with the front injector, see if the problem stays with the injector or the position.. then go from there.

[Martin]

I am assuming you have a fuel filter in the tank. Deteriorating fuel hoses can contribute to the problem hoses in the tank must be rated as submersible and ethanol compatible, external hoses must be ethanol and fuel injection compatible. Water can settle in the rail and if left it will rust, water combined with ethanol will also eventually form an acid..You might want to remove the fuel rail and check for debris and clean. Clean the rail by blowing into a clean white rag, you can then inspect for rust and or debris'
Regards Martin.

[goodworkmax]

There is a metal filter in the tank and yes the hoses are correct type.  I did clean the rail thoroughly when i did the injectors. I'll try swapping the problem injector with one of the others and see if it follows the injector as suggested by BrickMW.   Thanks

[Martin]

When you cleaned the injectors did you remove the internal filter screen.
Regards Martin.

[goodworkmax]

no i did not.  Is this inside the tank?

[Martin]

There is a small filter screen inside the injector. They can be removed by screwing in a self taping screw or self drilling screw that is large enough to grip the screen. you then pull the self taping screw with a pair of pliers or vice grips, this will extract the screen. Most of the time this will wreck the screen, however replacement screens and "O" rings can be sourced from injection specialists or Ebay..
Regards Martin.

[Vespa no more]

How is the injector?
As Martin said, there is a small filter / screen in the top of the injector.
Get a replacement first, then pull it out with screw. Once you've done one you will be very familiar with it. I screwed in and then put the head of the screw into a vice and pulled the injector... quite easy.
If you don't have the replacement screen, you can clear the screen by squirting from the base of the injector (reverse direction).
See on youtube for diy FI cleaning.
But make sure to end off with correct direction.
Use a small 9V battery - not a 12V. And don't keep it on for too long ... say 1 sec - can damage the FI (solenoid?)


Guy