Oil light comes on at low rpm.

My 1980 kz550 ltd. oil light has started coming on at idle but goes off when I give it gas. I just changed the oil and filter. Oil level is fine. A little over half way up between the two lines on glass oil level indicator. I've had this bike for three years and this is the first time this has happened. Does the oil pump get weak before it dies? What should I be looking at?
Thanks for all the help.

do you know where your sending unit is? maybe try pulling it apart and cleaning it

When I saw the thread title I knew it was going to be about a 550. I've had several motors that have done this, some with relatively low miles (5000 mis). I've never figured out why they did it, but I've never had a mechanical problem with them either (yet?).

If you want to try wireman's suggestion, I think that the sending unit is on the bottom of the motor, near the drain plug.

Oil weight/ viscosity can play into this. What oil are you using and the weight? Installing a pressure gauge to test the pressure is a good Idea, but could be to thin of oil. The switch could be a problem, and I would say that they are pretty inexpensive. But if oil weight is correct and you test the pressure and its low, then either the pump is worn or the bearing clearance is excessive at your crankshaft. Your manual will have the spec for oil pressure. You say "Low" RPM, what RPM is that? Is the Idle speed close to 1K?
If you look at this blow up of the pump and pressure regulator, you will see that the regulator, which dumps excessive pressure back to the sump, could possibly be stuck or a very weak/ broken spring. Group 24 in the picture.
Also while not shown in this picture there are O-Rings at the oil pan to motor for oil galley that could possibly leak some pressure back to the sump.


They are #14 in this picture.

I am using Quaker State 10 - 40 weight. I will check the things mentioned so far. Thank you. By low rpm I mean idle, yes, it idles at 1000 rpm.

I think that the idle speed spec for a 550 is 1300-1400 (going on my sometimes faulty memory), so you may want to adjust that.

I use 15/40 rotella in my bikes, and I've had at least three 550's that had this condition, all had less than 12,000 miles. The light goes off above 2000 rpm usually, but oil temp does affect it. It doesnt begin to illumunate until the bike has been run 15 minutes or more.

I also had it come on during highway riding once, I was maintaining 85 mph, riding w/passenger, for 40-45 min when that happened. That made me take notice. I pulled over and let it idle. It didnt make any bad noises (other than usual air cooled KZ stuff). I let it sit 15 min or so, ran it again at idle and all seemed normal. I resumed my ride, but at 70-75 mph and had no more problems.