1980 cb750 custom...my first ever 4 cylinder!

[Derek]

Well hello everyone, aquired this today and i am not quite sure what it is exactley as no paper work with it as of yet, as far as i know it is a,
1980 CB750 Custom
its in decent shape and apart from two leaking carbs and a seized up choke cable it will hopefully be running tomorrow, excited.
I never had a hankering for one of these but at $250 i couldn't pass on it and after going to look at it today i kinda really fell for it.

So here's hoping for main engine start tomorrow

[LukeM]

$250 is a steal for this bike, especially if you can get it running!!! The bike looks like it's in decent shape. I hope you get it running, and there's nothing seriously wrong with it.  

I heartily recommend you download the Factory Service manual found on the MANUALS section of this forum.  It is very good, and will help you solve just about anything wrong with your bike.

It shouldn't be hard to diagnose those 2 problems.  RE: the choke cable, let's hope it's just the cable that needs to be lubed, and not something frozen on the carb bank. Be advised that the choke cable is designed to slowly roll back to the OFF position.  At least mine did.  No matter how I tightened the tension thing for the choke, it would eventualy roll back to OFF.  I found out later it was designed to work that way.  If someone else has a different experience with this, please reply.

Leaking carbs may be needle valve sticking open, cracked fuel line at the carb bank, or perhaps a bad gasket between the float bowl and the main carb body. It depends on where it's leaking. Rebuild kits are readily available.  If you do take the carbs out, it would make sense to give them a thorough cleaning inside and out.  There are several postings on this forum on how to do it.  Re-run has done this at least once.  If you're like the rest of us, you will probably have the carbs in and out of the bike at least twice. There are some places who will clean the carbs with an ultrasonic machine.  I've heard that they come out extremely clean, all the way into the deepest darkest places.  Rice Paddy here in Columbus charges $65.  The liquid they use is a diluted solution of Simple Green and water.

My 1979 CB had a fuel manifold valve, that would shut off fuel flow when the engine wasn't running. It runs off of the vacuum tap on one of the carbs.  If you don't want to deal with that, you can bypass it, but you will need to be religious about using the petcock when you park the bike. I leave that up to you.

Change the oil, check the air filter, check the tire sidewalls, brake fluid, lights, fuses, all the other basic maintenance stuff.  I hope you get it running, and give us some updates on how you're coming along.  We're here to help if we can. Welcome to the forum!

Luke M

[TOOLS1]

Everything Luke just said, or send it to me
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[Derek]

Thanks for the welcome.
For info i am a brit and live in northern Minnesota, been here 10 years and i sold my Triumph T150v when i moved to the states, so 10 years without a bike and back in the day i would never have even considered one of these.
Removed parcel carrier and that screen thing today and threw them in the dumpster!!
Carbs off and airbox off for cleaning.
Washed her off and she really is in good shape and i am hoping to do the carbs this afternoon and see if she will fire up.
I will take pics and keep you all up to date.
Side panels are the only thing missing and a few bolts here and there, it has done 52,000 miles and tires are good and it does seem to have not been abused in its life.

So here's hoping when it runs it sounds good.
Question, them silencers on this bike, are they origional as far as you guys can tell?
seen various configurations and was wondering if they are stock desisn or not.

Anyway, thanks again for the welcome...:)

[Derek]

Yeah if i get sick of it I'll send it to you no problem...lol

[TOOLS1]

I think your exhaust is aftermarket, but I am not really familiar with the DOHC models.
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[Derek]

Great news, she fired up first turn but stilll fuel leaking from the over flows on two of the carbs, they are the rubber tipped shut off valves in the float chambers.
i cleaned up the seats carfully but the rubber looked a bit ribbed.
Anyway, we now know its worth spending a bit on to get her running good.

Smoked at first and ran rough, then cleared and ran superb, it even idles smooth too!!.
so delighted is all i can say.

everything works, indicators, all lights and horn etc
so i now have a want list, air filter, oil filter, air filter rubber connectors as these are perished and the needle valves (whatever they are callled) and side panels and that should be it.

unable to take it down the road coz of the fuel problems, but i have a real good feel about it.

Happy Chappie!

[Derek]

Ok here she is, with crap removed and cleaned up, fuel leak appears to have stopped, maybe dryness from being stood was the culprit with the leaks.

so just the fine detail now and i know i have got lucky with this machine.

[sgtslag]

V-e-r-y Nice!...  You stole that bike.     Enjoy it!  Cheers!

[Derek]

Just took it up the road for a gallop and chain and sprockets will need replacment, also balancing of the carbs, runs sweet but in the lower rpm range it is not as smooth as i think it should be.
Never having ridden oneof these before it hard to know how it should be, i am sure though it should be better than it is, which is understandable i guess.
Fuel leaks have gone, which is pleasing to say the least.

So, as you guys are the experts!!........what should i expect from it regarding fuel consumtion and general performance, i was never a hard rider but i do like to hear the motor working?

Brakes feel good and it feels solid and tight, other than the chain area which i feel sure will be shot when i investigate it further.

Derek

[TOOLS1]

With that bike in good tune, you should get 50-55 MPG. And yes it should run as smooth as a sewing machine.
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[Derek]

update on the beast,
all in all ok, however, Noisy clutch.
When Lever is pulled in the noise goes away, when released it sounds aweful.
I have downloaded the service manual etc and will be stripping the clutch side soon, just pointers on what to look for will helpful.

Cheers, Derek

[arko]

Real nice bike man!! I have just bought same type only mine is a 1981 model. Got it started for two weeks ago, after its been stored for 5 years. Good luck!!  This you can.... :-))

[seestheday]

Very good looking bike. Did you manage to get papers for it yet?

[arko]

Its not the original silencers you have on you bike as far as I can see. I try find a picture.