Just bought a '80 cb750k, couple of questions.

[nickajeglin]

Hello everyone, my name is Nick, and I just traded my 83 vt750c for a nice 1980 cb750k.

The po's story was that an old friend had a stroke a while back blah blah blabh... been in a barn for 5 years, blah blah, put aircraft fuel in to store it, etc.

It does look really really clean from what I can tell, zero rust in the tank, Oil looks and smells pristine, but they could have changed it. No rust visible anywhere, not even on what appears to be aftermarket 4-2 exhaust, no exhaust leaks, no smoke on startup, zero rust on chain or back sprocket, and back sprocket looks pretty nice from what I can tell.

I just drove it home, and it seemed to run well. A lot of valve noise compared to my vt, but I imagine that's probably normal since it's got the cams right up under the tank.

I was having trouble shifting, but I was wearing big steel toe boots, and I'm very much used to a nice loud clunk from the vt to let me know that I've shifted, the gears on this were very quiet. It looks like the carbs may be leaking a very small bit from what look like drain tubes on the bottom, but that's the only issue I can see right now. I'll pick up a clymer manual this week, and start working through fluid changes and tune up. Any advice on issues specific to this bike I should check on?

Also, it's got a fugly aftermarket windjammer fairing, does anyone know offhand what part's I'll need to dredge up to change it back to stock? The bike is in such great shape I kind of just want to clean it up and replace parts with original, but I'm not sure what all was discarded when the fairing went on. I imagine turn signals, headlight, and mounting brackets for that stuff?

Anyways, I'll post some pics later today or tomorrow, It really is a great looking bike, especially for having been in
nebraska for so long.

 Also, I think I kind of want to go back to stock exhaust at some point, since I think that the 4 into 4 mufflers look way sexy. Will most years of factory exhausts fit on this, or is there a particular set of years that have common parts, or maybe like a series number? Additionally, will I have to rejet if I go back to original?

Thanks,
Nick

[TOOLS1]

Hey Nick
The valve noise is probably the carbs needing synced. When they are out of sync the engine will sound like it is going to fly apart.
On the faring removal it all depends on what was removed. Sometimes they leave the headlight ears, sometimes not.
On the manual, you can download the factory manual from the home page here for free. It's a lot better then the Clymer.
An original exhaust is going to be $$$$$$$$$$$$$$$$$$$$$$$$$ if you can find one. However I do have a set hanging in the shed I might be willing to part with. Not the best of shape, but still pretty useable.
TOOLS

[shinyribs]

Nothing to say that Tools hasn't already said. Except the valve noise could possibly be cam chain noise. The FSM (Factory Service Manual) will detail how to go about adjusting that.


Fellow member here, Seestheday, has made some nice videos on these bikes that you can find in the Repair Sources and Write-ups section.

Here are a few links:

http://honda-cb750-s.456789.n3.nabble.com/I-made-a-few-videos-and-bought-a-domain-name-td4040818.html

http://honda-cb750-s.456789.n3.nabble.com/Video-adjusting-checking-valve-clearance-DOHC-td4040843.html

Welcome in,Nick!

[nickajeglin]

Thanks for the links and tips, I'm probably going to ride it around a bit this weekend, just to get a feel for it, and see if any issues pop up.

Here's some pics!!








Last pic is the little tubes that are leaking on the bottom of the carbs. Looks like it's mostly the two inside ones that are doing it to me.

On the exhaust, the more I look at this the more I think it's ok. I think you're right about $$$$$ and It's unlikely I"ll find some in as nice of shape as the current one is. I guess for now it's "if it's not broke, don't fix it."

[shinyribs]

Nice looking bike for sure! Get ya some hoses on those carb overflow nipples. Keeps the fuel from dripping on the motor and...well,you know.

If you ever decide to swap pipes keep me in mind. I have a set of 4-2 pipes in good shape. Factory double wall head pipes that prevent the chrome from turning blue due to heat.

[TOOLS1]

Those pipes being so blue, tells me that the bike is jetted very lean.
TOOLS

[icerigger]

The leaking form the overflow is either the needle valve sticking/not seating or cracked overflow tubes. Rap on the bowl with a screwdriver handle to see if you can get the needle valve to seat. If not you'll have to clean the carbs, checking the overflow tubes for cracks.

 

[nickajeglin]

I rode it around a little bit today. It felt pretty awesome, a little vibration at high revs, but I assume that that could be fixed via some simple tuning. After a while it died out on the highway, I about panicked, but had the presence of mind to pop the clutch in 4th before it stopped rolling, It had very little power, but if I kept the revs about at 3500 it would keep moving. It finally died for for sure a few miles later.

I pulled the battery, andnoticed it's brand new and has a trickle charger hookup dealie attached to it. When I got it home and checked it with a multimeter it showed 5v....4v.....3v.....2...1. This makes me suspect the charging system. PO must've had it on a charger, and it ran off the battery all day, then died when it was drained. Should I suspect the rotor/stator off the bat, or could the regulator have caused this? I'll check them all of course, I just like to know when I'm on the right track. If it is the rotor/stator, is replacement the only option? I could've swore that I saw somebody talking about rewinding the coils DIY style.

TOOLS: Would someone not having rejetted it after changing the pipes caused it to run lean?  Or is that backwards?

Thanks for the tips, you know it's a great forum when people are already giving you some help just from seeing the first pictures of the bike. I'm currently charging the battery, and a buddy is bringing a fresh one down so I don't have to leave the bike out overnight.

[free2ride]

what else can I say? nice bike! and this is the place to find out ways to make it "nicer"

[motogrady]

ha, my first 750k, it was a used k model, carried a 2nd battery wherever I went.

Never did figure out the no charge issue on that one.

You have a charging issue, they get low on battery they run like crap then die.

As far a jetting, a different pipe may move more air thru the motor, making it run lean.

With a 4x1 pipe on my '79 f I've got 75/110s, and still feel they could be a bit bigger.

[nickajeglin]

Turns out that my friend who brought me the (dead) battery last night has a nearly complete 79 or 81 cb750c that he has all taken apart, he's willing to give it to me if I will reassemble his current bike, a cbr. I may just give him cash... putting together what someone else has taken apart is a nightmare.

Anyways, now once I track down the charging problem, I'll have spare parts!

[free2ride]

nickajeglin wrote

Anyways, now once I track down the charging problem, I'll have spare parts!

good luck! I wind up buying a new battery every second year