About 3 months ago I had Avon tires put on my 2007 Wide Glide. The Cobra MH90-21 was put on the front. From the beginning that tire has been leaking about 1/2 pound of air a day. I bought 2 new quality pressure gauges to confirm it. To try to fix the leak I had the tube, rim strip and valve replaced. It still leaks. Is that kind of leak normal for skinny tires? Other than a protruding spoke, what could be causing the leak? How can it be fixed?

 

Not normal and you need to put the tube under water to find it. Put some dish soap in the valve. It might be loose.

 

Or just install a new tube?

 

As I read the OP it looks like the tube and valve stem have been replaced already so can only be a couple of things,

a) you bought cheap *** tubes, get a brand name
b) there's something in the tire causing another leak with the new tube, note orientation of the tube to tire, find the leak in the tube and check that part of the tire or look for debris inside the tire.
c) your installer doesn't know how to install a tube without pinching it - find new shop.
d) you have bad luck and ran over something again. SOL - LOL

 

+1
I would do this test with the tube by itself, off of the rim, and then, if it doesn't leak, do it again with the tire mounted on the wheel. Submerge the wheel in water so the valve stem is completely submerged and check for leaks. If it's not the valve stem, rotate the wheel so every part of the wheel gets submerged up past the spoke holes and check for leaks.
Make sure the valve stem cap is on when you do the tests. It might be possible that the valve stem cap is causing the valve to leak.

 

My guess would be the protruding spoke

 

Tubeless fixes most of these issues, thats why I have them on my WG

 

Tubeless tires still require tubes and rim strips when mounted on laced wheels.

 

Just put some spit on the valve stem top and if it bubbles,the valve core is bad so replace it. If the mechanic that replaced the tube for you, used the old valve core then the leak would still happen in a new tube. If it isn't the valve core then you need to break the tire down and check the tube in a immersion tank and your wheel for a spoke that needs to be tightened or replaced.