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Author Topic: First bike 72 CB500 K1 oil light problem.  (Read 514 times)

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Offline glenymact

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First bike 72 CB500 K1 oil light problem.
« on: June 25, 2022, 05:45:41 PM »
Hi all,

I am new to the forum I live in St. Catharine's Ontario Canada (tried to figure out the SOHC forum map but couldnt find out how to eddit it). Just bought a 72 CB500 (odometer shows 16k miles but is not original), took it too an experience mechanic whose business was focused on classic cars and bikes and he seemed to know what he was doing. Safetied the bike and got it registered. He changed the oil 20w50, replaced the fork seals and the fork oil, adjusted intake and exhaust valve lash.

The bike has run fine for a few rides, and then i noticed once warmed up the oil light would come on when down shifting and slowing and the bike wouldn't hold idle (it was set to about 900rpm). I adjusted the idle to be a bit higher 1100 and the problem went away. after some time the problem resurfaced and now my oil light comes on only when the bike has been heated up. Last ride the light would stay on until 3k rpms after i got it nice and hot.

from a bit of research i am thinking that the oil switch might be due for a change or at least a cleaning i am not sure if you clean them or just replace them. I am leaning towards the switch because it starts behaving differently once its heated up. Again i am a complete noob and would imagine my guesses or ideas could be way off base and would benefit from a more experienced person. PO said he sent the carbs away to be rebuilt last summer but i read a whole forum post about a hanging idle that was resolved by a carb cleaning.

i have read that i can open the tapet covers while running and check if oil is making it up to the valves, i have yet to check that. Any thoughts?
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72 CB500 K1

Online newday777

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Re: First bike 72 CB500 K1 oil light problem.
« Reply #1 on: June 25, 2022, 06:25:36 PM »
Welcome aboard glenymact
It sounds like it could be the pressure switch,  or, it could be the oil in it. What brand and weight was put in?
New oil filter too?
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Stu
Honda Parts manager in the mid 1970s Nashua Honda
My current rides
1975 K5 Planet Blue my summer ride, it was a friend's bike I worked with at the Honda shop in 76, lots of fun to be on it again
1976 K6 Anteres Red rebuilding project, was originally my brother's that I set up from the crate, it'll breath again soon!
Project 750s, 2 K4, 2 K6, 1 K8
2008 GL1800 my daily ride and cross country runner

Prior bikes....
1972 Suzuki GT380 I had charge of it for a year in 1973 while my friend was deployed and learned to love street riding....
New CB450 K7 after my friend returned...
New CB750 K5 Planet Blue, demise by ex cousin in law at 9,000 miles...
New CB750 K6 Anteres Red, to replace the totaled K5, I sold this K6 at 45k in 1983, I had heavily modified it, many great memories on it and have missed it greatly.....
1983 GL1100A, 1999 GL1500 SE, 1999 GL1500A

Offline MD

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Re: First bike 72 CB500 K1 oil light problem.
« Reply #2 on: June 25, 2022, 07:01:33 PM »
Welcome from the Arrowhead Region of Minnesota,

Double check the oil level.  Low oil will result in the oil light coming on at lower rpms.

-MD
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1975 CB550F Super Sport;  Lake Superior Circle 1000, 45-90 Saddle 1000, All in Yooper 1000 and SS 2000 in 48 hrs:  1985 GL1200A, MN in State SS1K

Offline tool14

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Re: First bike 72 CB500 K1 oil light problem.
« Reply #3 on: June 26, 2022, 05:16:34 AM »
welcome aboard
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Offline glenymact

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Re: First bike 72 CB500 K1 oil light problem.
« Reply #4 on: June 27, 2022, 12:41:44 PM »
Newday777 i called my mechanic and he said it was lucas brand 20w50. I described the symptoms to him and he thought could be the switch could be the pump. so i am going to try the switch first. i ordered more oil before i spoke with him and just cruised these forums to find a brand. Wound up going with Spectro 20W50 motorcycle oil its mineral oil. My mechanic said i could try lucas treatment, which is an oil additive that thickens the oil, if i am having oil pressure issues. I will start with a new switch and see if the issue goes away. I also want to try cleaning my carbs at some point. because i found a new issue last night. Throttle response would jump from 5k rpms to 7-8k rpms and then drop down again without any real response from the bike. I have to test the clutch to make sure it is fine but i think its a fuel delivery problem. gonna have to actually get into it instead of just supposing.
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72 CB500 K1

Online newday777

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Re: First bike 72 CB500 K1 oil light problem.
« Reply #5 on: July 13, 2022, 04:52:18 AM »
I think the Lucas additives have friction modifiers in it and you many have slipping clutch from it if their oil has friction modifiers in it too.
That will require you to flush the engine. Go out and get a gallon of Rotella T4 15w40 oil(yes it is diesel oil but works great in our engines with wet clutch as there are no friction modifiers) and a can of Seafoam treatment (both available at Walmart). Warm up the bike, then drain the oil out, change the pressure switch and drain the filter case (reuse the filter), then put in the whole can of Seafoam first and then fill the oil to top line. Go for a 100-200 mile ride(one ride) to fully heat the motor and flush the clutch plates clean(keep RPMs below 2,500! Do lots of shiftingup and down). Then go home and drain the oil while it's still hot. Change the filter and fresh oil. Should be good to go then.
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Stu
Honda Parts manager in the mid 1970s Nashua Honda
My current rides
1975 K5 Planet Blue my summer ride, it was a friend's bike I worked with at the Honda shop in 76, lots of fun to be on it again
1976 K6 Anteres Red rebuilding project, was originally my brother's that I set up from the crate, it'll breath again soon!
Project 750s, 2 K4, 2 K6, 1 K8
2008 GL1800 my daily ride and cross country runner

Prior bikes....
1972 Suzuki GT380 I had charge of it for a year in 1973 while my friend was deployed and learned to love street riding....
New CB450 K7 after my friend returned...
New CB750 K5 Planet Blue, demise by ex cousin in law at 9,000 miles...
New CB750 K6 Anteres Red, to replace the totaled K5, I sold this K6 at 45k in 1983, I had heavily modified it, many great memories on it and have missed it greatly.....
1983 GL1100A, 1999 GL1500 SE, 1999 GL1500A

Offline BenelliSEI

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Re: First bike 72 CB500 K1 oil light problem.
« Reply #6 on: July 13, 2022, 05:13:28 AM »
I’d check your clutch adjustment before anything else. Do you have a workshop manual for your bike? Clutch adjustment is an easy task. Read the section and then ask if you have questions.

Don’t make “carb cleaning” your first job on the bike. It’s more work than you might think.
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