Topic: CB750 oil light

[Noah]

Hi everyone, I recently picked up a '73 CB750 which I'm fixing up to use as a weekend rider.  So far things have gone fairly smooth but one of the last things I'm having a problem with is the oil light.  When the ignition is turned on, the light comes on as it should.  After the bike is started, it goes off.  After about 10 minutes of riding (outside temps 70-80 degrees), the light will come on when I stop for a stop sign and the RPM's fall under 2000.  As soon as I accelerate and the RPMs go back up, the light goes off.  I haven't rode it more than 20-30 minutes, but toward the end of that ride, the light would start coming on under 3000 RPM.  There are no unusual noises coming from the engine and it rides smoothly. The bike has new oil (20w50), a new oil filter and I also changed out the oil pressure switch with one from another '73 I'm using as a parts bike, but it didn't make any difference. I don't see any oil leaks anywhere. Could this indicate a bad oil pump? Any ideas or suggestions would be appreciated!

[ekpent]

Hmm kinda spooky. How many miles is the odometer showing.Any know history on the bike like if the cases have ever been split or major engine work done.Peek inside the oil tank when its running sometime and visually check to see if you are getting a good circulation. Hooking up an oil pressure guage would be really helpful to give you some real numbers and data.

[bollingball]

+1 On a gauge it will tell you what is going on better than a (idiot) light. A cheap $10 one is better than the light.
I would not run it until it is resolved. It may only need new orings in the pump and at the Trans. shifter area.

Read this post don't worry about drilling the hub just yet but do the orings if that does it then drill the hub maybe in the winter.

http://forums.sohc4.net/index.php?topic=78643.0

                                    Ken

[Tintop]

great link bollingball, thanks for posting, and to the OP for the thread.  Will make the oil hole mod when I rebuild the K3.