[Nebraska-man49]

I do not own this bike, but I am trying to help a friend who bought it. He got the bike several months ago, I went with him to check it out. Cosmetically this bike is absolutely excellent condition. The guy who sold it buys and restores older bikes and he got it from an older guy who had bought it new but it had been sitting stored for a number of years.
The seller said he had rebuilt the carbs, repaired leaking fork seals, new tires, and a few other things. Because it was winter and snow-covered streets my friend did not ride the bike but listened to it idle and questioned the seller pretty extensively. We returned a month or so later when the snow cleared but the weather was still quite cold so we trailered it. The seller started and drove the bike up on the trailer for us. so it seemed to be running ok.
After getting it home and unloading it (it wouldn't start) it had a weak/bad battery. Got a new battery installed but still having issues getting it started. One of the issues is it has been very cold here and he has been told that these bikes are very cold-blooded.
Now I am going to have him bring the bike to me and I will start digging into the problems. From what I am hearing I think is carb/fuel issues but I suppose it could be vacuum problems also. Could it be the on, off, or reserve fuel valve?
Any suggestions as to what else I can start looking at would be greatly appreciated. I know this is a very lengthy and wordy post so apologies, please.

 

[Randall-in-Mpls]

Models with a vacuum-actuated petcock, like your Silverwing, can be hesitant to start if they've sat long enough for fuel to evaporate from the bowls (sometimes as little as a few days.)
Beginning with a fully charged battery, turn the key switch ON, open the petcock, and leave the kill switch OFF.
Crank the starter in short (2-3 second) bursts until the oil pressure warning light goes out. That should have applied vacuum long enough for the bowls to fill.
Turn the kill switch ON, and if all is in order, it will fire right off.
Depending on fuel quality, you might need to purge old, stale fuel from the bowls before this procedure.

 

[richnct]

Check the rubber vacuum hose to the fuel valve. If old they develop splits on the hose ends and reduce vacuum applied to the valve diaphragm. This can manifest itself as poor starting but still run if it starts. Additionally, applying vacuum to the vac hose, or pressure to the atmospheric hose should operate the fuel valve. By mouth or with a syringe works, that low level of force. With the carb drains open this can demonstrate the valve is functioning and also provide new gas to the carb bowls.

 

[Sidecar Bob]

What they said ^^^
My preferred method is to
1) make sure the carbs are empty (place a container under the overflow/drain hoses and open each drain screw until fuel stops flowing out of the hose)
2) disconnect the fuel line from the petcock (what you called the "on, off, or reserve fuel valve")
3) Attach a funnel to the fuel line and add 90cc of fuel directly to the carbs
4) re-attach the line to the petcock
This will fill the bowls and it should start as easily as if it was run yesterday.

As for being "cold blooded", I ride mine in the winter and until I retired I drove it to work every day in the cold half of the year in Southern Ontario no matter what the temperature. Google says it is above freezing in Nebraska today so that shouldn't be an issue once the carbs are filled (unless there is something else wrong)

Welcome to the forum. At this point I would usually ask you to add your location and your bike's model and model year to your profile so that you don't have to remember to tell us every time and we don't have to keep asking when you forget (see Forum Settings link in my signature).
In this case I would recommend encouraging your friend to join so that he can avail himself of the forum's resources directly.

And welcome to the world of antique vehicle ownership (they own us, not the other way around). Your friend's bike is about 4 decades old and the Previous Owners may or may not have had all of the maintenance necessary to keep it safe & reliable (especially the "restorer" who intended to sell it when done) so it is highly recommended to download the Factory Shop Manual for your model (available through the CX Wiki - link in my signature) and go through all of the service procedures, regardless of whether your bike has reached the specified mileage.
Note that while aftermarket shop manuals are pretty much necessary for people without factory training to work on a lot of makes & models of bike the FSMs for the CX/GL500/650 family of bikes are so well written & laid out that the FSM is really the only book you need and and even the best aftermarket books are secondary references at best.

I also recommend looking on all rubber parts with suspicion because rubber does not age gracefully. Check the date codes on the tires and replace them if they are over 5 years old no matter how good they look & feel (old rubber simply cannot flow around the irregularities in the asphalt well enough to grip, especially if it is cool or wet). The original rubber brake lines should be replaced every 2 or 3 fluid changes (= 5 or 6 years) so if the bike still has them I recommend shopping for modern stainless braided ones (they last practically forever and double the life of the fluid). And don't forget things like the rad hoses and the boot between the engine and swingarm (they can crack on the bottom where you don't see it).

Oh, and we like looking at pictures of other people's bikes here so