TOPIC:

Hello guys, I just ride my bike today for the first time of the year.. and the oil light has pop in the cluster.. I pull the bike in 3rd gear at 8000rpm and bang oil light stay on all the time. I rode it for 100miles without any trouble.. oil level is perfect. Engine is running like brand new(he’s brand new) .. Don’t understand at all!! I put Car oil in it and the clutch is slipping yesss, maybe wrong adjusted or wrong oil?! (castrol 20w-50) thank you for your advice 

You should pull the oil pressure switch and put an oil pressure guage on it to see what your oil pressure is. Hopefully, you just have a bad oil pressure switch, but don't ride it till you check with a pressure guage.

Your light being on is a bit worrisome as you just rebuilt your engine.

This guage should work.

www.canadiantire.ca/en/pdp/equus-90-degr...l+pressure+gauge#srp

You should probably switch out your oil to a motorcycle oil. Just grab Kawasaki 20w-50 Motorcycle oil.
I bought a 1 gallon jug for about $30 here in the states.


Oh, and put your motorcycle info in your signature. Otherwise, we have to go through your previous posts to figure out what bike you have.

 

Thank you,  but  if the oil pressure were bad, I will have break my engine in 100miles ?! No knock sound, no heat.. it’s weird 

You never know..but with oil pressure...you never take the chance.
You kill the engine and figure out what the problem is unless you have money.

Pull your timing cover plate and see if the wiring to the oil pressure switch is ok.
 

Your oil pressure light is there for a reason - ignoring it if the switch is not faulty will be a very expensive lesson.  It may already be a moderately expensive lesson.

I had same thing happen maybe 20 years ago. Same bike 1980 kz750 e1.
problem was orange blue wire connection at the pressure switch. 
like F64 said remove the timing cover and pickup plate and clean that connection and particularly clean that non metalic area around the connection.  I had nothing visible but figure the connection was grounding out via corrosion or crud or moisture. Cant remember exactly but a good clean did the fix.

ps. The oil switch is like the neutral switch in that operation breaks the ground and the light goes out

good luck



 

Alternate the ground lead on the back of the oil pressure switch between ground and not with the ignition on and the idiot light should be on when it's grounded and off when it's not.
That'll tell you if you have a wiring/bulb or a switch issue. 
Oil pressure switches are not really serviceable so a new one is the easiest option. Or if you want to try and save your existing one you'll need to clean up the plunger shaft, reattach the lead and test with the oil pressure switch touching a ground and pushing the the plunger in and out watching what happens to the idiot light. 

Had the same problem on my 750H last year. Stopped the bike immediately and took the timing cover off. Turned out the timing plate was pressing against the lead and grounding it - I wasn't careful enough when I put everything back together. Took the plate off and moved the wire out from under it and had no more problems. Still put the pressure gauge on when I got home to double-check though. The pressure gauge can be screwed in to the side of the crankcase (where the plug is in the picture below). Putting it in instead of the pressure switch won't work as you won't be able to mount the timing plate.

Warren: The 750's have a different pressure switch. No plunger so replacement is the only option if it's shot.

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Thank you guys, so you talk about neutral switch. That switch is near the front sprocket if I remember?! And my oil pressure switch ls under timing cover?!  I forgot to mention that It happens when Realise that my clutch was slipping like hell at 7-8000rpm !!? Light never goes out after that

Yes. Oil switch is under the timing cover. Right hand side. Download the manual for gpz750

Does OIL CAR can cause my oil light ?!  I put that in it

The car oil shouldn't cause your oil light to come on but it will cause your clutch to slip.