Topic: 1973 CB500 Restoration - Wrencher New to Bikes -

[erranttraveler]

I had the great fortune of picking up a 1973 CB500 in pretty decent condition. I'm planning on cleaning it up and using it as a daily rider while slowly improving its performance. I'm new to wrenching on bikes, but in the past I had a 1969 VW Squareback and a mid-nineties Volvo that taught me how to work on vehicles.

I'll be posting here as much as possible and sharing my project in the hope that it can help others with similar projects and so that I can learn from all of your collective knowledge.

The initial assessment goes something like this:

• Bike runs, but the petcock needs rebuilding/replacement as it has been leaking fuel into the engine for an undetermined amount of time.
• The PO said that he was riding it pretty much every day, but that it would 'overheat' in traffic.
• The exhaust is a 4 into 2 and not the original
• The electrical system seems to be in decent shape (thank god!) and it stars right up and all lights, etc. work
• It seems to have been leaking slightly from one side of the head and will need the head gasket replaced this winter
• It recently had the breaks 're-done' but the rear break offers nearly no help when trying to stop the bike and the front pads squeak and squeal when pushing the bike
• The carbs were recently sync'd, so hopefully I won't have to do this for a while
• The tires are brand new as well

[TwoBigCats]

congrats! i bought one when i returned from SEA in late '75 ... fun bike with a great sounding motor. enjoy refreshing and riding it.

[JimS63]

Sounds like it won't take you too much time/money to get it up and running reliably! Except for the head gasket that is. Good luck with your project!

[erranttraveler]

Well, I was hoping for a nice birthday present of being able to ride around legally (got my plates and registration last week) and with a fixed petcock, but it was not to be.

I got a new replacement gasket (16955-268-020 and about $4 including tax) for the petcock and installed it and checked the cup and the ports of the petcock assembly. The old gasket was cracked and was a bit worn around the seal for one of the ports, so I was hoping that the brand new one would address the slow leak out of the front-most nipple. Once I replaced the gasket I put some fuel back in the tank and tested the flow on primary, reserve, and closed valve settings. The flow was improved after I cleaned out the petcock assembly and fuel cup with a few blasts of carb cleaner, but there was still a slow dripping leak out of the front nipple even when the valve was fully closed. Bummer.

When I had the gasket off, I noticed that the ports seemed to have a bit of uneven wear around the circumference of the holes, so I'm thinking that this is what is causing the slow leak. It now looks like I'll have to replace the whole assembly, alas.

After discovering this bad news,  I reconnected the fuel lines, put the tank back on and I was looking forward to at least being able to get out on the road for a bit after doing an oil change last week. My plans were thwarted, however, when the bike failed to start up for me. I got a couple good tries in with the electric starter where it tried to turn over and cough to life, but after about the third attempt, every time I tried the starter the solenoid would click and the starter would whirr a bit, but the engine wouldn't turn over. I tried knocking on the starter with my fists, but this didn't work, then I tried to use the kick starter, but that didn't work, and finally I tried a bump start, which seemed to yield the closest thing to an actual start, but my legs and lungs gave up (no real hill near where the bike is garaged) before I could get it running. (NOTE: it was in 'run', the choke was open, the fuel valve set to ON (and tried RES), and the ignition on, jfyi)

The lights all worked with the ignition on, so the battery did have some juice, but I'm thinking letting it sit untended for about a week might have been too much and that the battery is on its way out.

I'm hoping that's the only thing it is, and I'll hopefully have time tomorrow to try a different battery and see if it will fire up with that. If any of you guys think it might be something else, please let me know.

In the meantime, to save myself the hassle/expense of having to change the oil again since the petcock is still leaking, I setup a little device consisting of a long funnel and a soda bottle to catch the slow leaking gas from the petcock nipples.

I'll updated more soon, and hopefully be able to post a video of it running and a few more pictures.

[rb550four]

Bummer. Did you check the kill switch to see if ya may have bumped it to the kill position? Sounds stupid right? I do it all the time.

[erranttraveler]

So, another weekend, another step closer to getting her running.

I got a brand new petcock in the mail on Friday and installed it on Saturday, but the leak persisted! The guy I bought the petcock from sent me a smaller set of washers/gaskets for the two screws that mount the petcock to the tank than what the parts guide called for, and I couldn't get them to fit the screws, so I used the old gaskets... Big mistake, they seem to be the root of my leak, since the brand new petcock continues to leak on me (albeit more slowly). I talked to the guy I ordered the parts from, and he suggested I file down the centers of the gaskets/washers and then thread them on the screws... I'll try that this week and see if they work.

I also borrowed a battery charger and re-charged the battery, which allowed me enough juice to get the engine fired up, but it was running terribly and coughed out after only a few minutes of idle with the choke closed. I discovered later, that the issue was even greater than the battery: I have a totally melted spark plug wire that severed the connection between the cap and the wire on the #3 cylinder plug wire. Bummer.

There's a photo below of what's left of the coil wire.

I don't really want to spring for a new coil, as I think the coil works just fine, but I'd love to hear your advice. Should I just suck it up and buy a new/used coil or try to repair the one I've got with some solder and a wire splice (realizing, of course, that this is a very temporary fix)? The other coil wires are pretty stiff and I'm afraid another one might go at some point soon.

I really want to get out on the road and ride before it gets any colder, but I know I'll have to replace the coil eventually. What do you all think?

Also, any idea what could have caused only the #3 coil wire to melt? Is there something up with the electrical system I should be wary of?

[Stev-o]

First off, welcome.  The end of the wire is the spark plug side, correct? If yes, buy four new caps and cut off a very short amount of the wire and screw the new cap on. Get em at the dealer, about $3 each.

These bikes need a good battery to run, so you may want to put that on your shopping list (about $50). 

Need to fix that fuel leak, that is a safety issue. Don't be discouraged, these are all minor issues.

[erranttraveler]

Hi Stev-o, thanks for the welcome, it's good to be posting on here instead of just lurking.

I'll get the caps and replace the ones that are there. The spark plugs are pretty new, I think, so hopefully new caps will be all that's needed on the ignition side of things.

Also, I'm keeping all my fingers crossed that putting the new gaskets on the mounting screws for the petcock will once and for all end the fuel leak.

Any suggestions for a good replacement battery for this bike? I was looking at this sealed one here www [dot] batterystuff.com/powersports-batteries/sYT12C.html, but it seems a bit expensive.

Thanks!

[Stev-o]

If you haven't changed the spark plugs, consider doing that too. Actually, a full "3000 mile tune up" would be a good idea and rule out possible issues. 

The scorpion battery is good, I have one in my K4.  I like the fact that it won't spill acid since it is sealed. $59 for that is a good buy. I also have bought Sears Die Hard batteries, they run about $50.

[erranttraveler]

Getting close to halloween and only marginally closer to getting the 500 on the street.

I couldn't find the AGM Scorpion battery in stock anywhere, so I ended up ordering a Shorai lithium battery (LFX14A5-BS12). It's a bit expensive, but it will hopefully last for a long time, and it certainly has a ton of power. I was able to find time today to install the battery, fix the leaky petcock, check the spark on all the plugs (it was fine), test the compression (it was low), and adjust the valves.

After all of that, however, I still can't take her out. Here's what I'm experiencing:

I can get it up and running, but it isn't idling very consistently, and needs throttle input to keep running. The biggest problem seems to be manifesting as very hot headers coming out of the 1 and 4 cylinders, and icy cold pipes out of 2 and 3. I realize this could have been a spark issue, but I made it a point to test all the cables and each produced what looked to be a strong spark. The compression was low (80psi) on all the cylinders, but equally so, which I think was due to my improper technique (I only figured out after doing the compression test that you have to crack the throttle open when you are turning it over to get an accurate reading). There might be a general problem with the coil. Also, the spark plugs were totally black, and two seemed to be a little wet with oil (bad news, I know).

Also, when I rev the engine it sounds fine, but when I engage the clutch, I have to rev it very high in order to move the bike forward, and it stalls out after moving forward only about a foot, no matter how much I crank the throttle. There's just a complete drop in power under full throttle with the clutch engaged. It's nothing like what this guy (http://forums.sohc4.net/index.php?topic=111602.0) is experiencing, since it revs solidly in neutral.

I will do a carb cleaning and see if the problem persists, but I think I might want to order a new(used) coil and replace the spark plugs as Stev-o suggested, to make sure that's not the problem. When I removed the points cover to do the valve adjustment, I saw that the points were brand new.

I'm also thinking it might be a fuel flow issue. When I replaced the petcock, the fuel sometimes flows smoothly out of both petcock nipples, but sometimes only flows out of the front nipple. Is that normal?

I know there are still many things that I need to work through to isolate the issue, but if anyone has run into a similar problem, I'd love to hear how you dealt with it.

Thanks!

[Stev-o]

If your pipes are cold, those cylinders are not firing.  Change plugs/caps and trim plug wires a quarter inch. Good luck.

[disco]

"If your pipes are cold, those cylinders are not firing.  Change plugs/caps and trim plug wires a quarter inch. Good luck."

Not necessarily if there's no fuel getting in you'll also have cold exhausts. I had same thing occurring on my CB750K6. I initially thought it was a spark issue & was going down that path checking points, connections, coils etc. I finally replaced the carbs with another set  and what a difference!! It has transformed the bike. It now has power all across the rev range. The throttle feels crisp & instantaneous.

I checked the old set of carbs & found fuel deposits blocking vital orifices.