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New Member, just got my '81 CB750C home!

mwp309

Been Ridin' A While...
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Hi all, just got home with my new to me 1980 cb750custom. It has a very reasonable 25K on the odometer. Has been sitting covered for the past 3 yrs in a garage. I was surprised to see it has a nice custom stainless steel 4 into 1 exhaust and the cheap emgo pod filters. Needs a little love, but is very nice for the half a thousand I paid for it! Gotta learn what to do before I try to start it, I'm thinking that a little oil in each cylinder, fresh oil and filter in the sump, fresh gas with a little seafoam in it, of course a new battery, anything I may be missing? Too dark to take pix, will try tomorrow. It's nice for it's 32 yrs!
Oops, my header says '81 but it's an '80.
 
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I believe those carbs have a vacuum activated valve on them so it may take alot of cranking before you even get fuel to the bowls. You'll probably want to take a look into the tank and see if its clean or rusted inside. The carbs will probably need to be cleaned if its been sitting a while. keep us posted on how it goes.
 
Thanks Andy, was going to drain gas tank this am. Can't wait to go out to the garage, it's all of 34 degrees today! Thanks for the info about the vacuum valve on the carbs, the PO did warn me that it is a mother to start in the springtime. Any way to bypass the vacuum valve and force feed gas into the carbs? Save my battery a bit of hard labor that way.
 
You can bypass the fuel valve. I believe the vacuum on it attaches to the #2 intake, and the valve itself sits just above the 3 and 4 carbs. It is possible to remove it and just gravity feed the carbs. I believe they actually refer to that valve as the sos "spawn of satan" on some of the dohc honda forums. I think there is even a write up with pictures on cb750c.com.
 
Didn't see any vacuum valve that jumpped out at me, however, after a day and a half working on it, I got it to fire up using my neighbor's jump box. Pulled the battery, new in 2008 and never used, got it on a charger to see if it will hold enough juice to start the bike tomorrow am.
 
Old battery won't hold a charge. Replaced the battery with an AGM sealed unit. Got it to fire, won't stay running. Throttle is sticky, but by manhandling it, I was able to go around the block! Gotta keep goosing it to keep it running. All my fooling around, I drained the new battery! Got it on the trickle charger and will try again tomorrow, hopefully the seafoam in the gas will help clean any gunk out of the carbs and it will actually run better.
 
i got the same bike last year and rode it a few times and just keep having issues. 1st it didnt wanna stay running and kept flooding too, so i took the carbs off opend em up and cleanded em and it ran fine. then it started having a charging issue so i kept jumpin it to ride and then i opened it up and found the alternator and stator are scuffed up from rubbing together. but replaced the battery and keep checkin with meter and it is charging still so i rode it around town then the turn signals stopped working. gonna try a new flasher relay and see if it works. if not i might have more electrical issues than i can work on. im mechanicly inclined but wires are like spagetti to me they all look the same. gonna have to get some wiring pictures to understand i cant figure out the blueprint style schematics.
 
Check your ground wires under the seat on top of rear fender clean conections make sure their tight i had same issue with my 80 750 custom turn signals would work then not ground wires a notorius for this.when looking at schematics follow colors from source to function it will help you to understand them better. Good luck!😳
 
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