Where is the vacuum line to the Fuel Pressure Regulator located on a 85 K110RT?

Anyone have a picture?

Don't have a pic but if you look at the throttle bodies, each of the intakes has a small vacuum takeoff spigot. 1, 2 & 3 will be blanked off with a rubber cap. No.4 has a vacuum line attached (probably encased in a protective wire spring) which goes around the end of the TBs (where your TPS is) and connects to your FPR located behind the TBs
EDIT: found this pic on another thread. The vacuum line is the one in the wire spring.

An '85 probably won't have the wire spring, but the hose will be as in Captain's picture.

Paul.

Why is there a spring around that line in post-85 m/c?  It seems to be a protective measure, but protection from what?  My 1985 bike does not have it, and I've never seen the need for a spring there.  What am I missing?

The short answer is it stops the vacuum tube collapsing on itself when the negative pressure inside increases. The spring casing holds the tube in it's round shape which is a very strong compared to being oval. When a rubber tube bends around a corner it tends to flatten out and can kink.

The long answer... Injectors rely on a constant pressure to deliver the correct amount of fuel. When the vacuum increases in the intake manifold under accelleration the flow of fuel will increases due to a change in the pressure differential between the fuel rail and the injector nozzle. The vacuum tube relays this change in pressure to the FPR so it can regulate the fuel pressure to maintai the correct flow thru the injectors. If the tube collapses/kinks, the FPR won't be able to adjust the fuel pressure and the mix will become very rich when accellerating.

Early machines do not have this spring. Later ones do.  I suppose it's a worthwhile retrofit then, even if my 1985 K100RS apparently never has experienced any problem that could be put down to a lack of spring on this vacuum line.

I'm not sure, but you may not even notice if there was a problem. Dirty emmissions, slightly poorer acceleration, increased fuel consumption especially if your heavy on the throttle. Certainly wouldn't be very common.

It's my understanding that the spring is there to keep the tube in the round (so no kinks) for optimal vacuum operation.