I am trying to track down an issue with my drive train that I've been trying to fix for a few weeks. I have a single speed setup with freewheel and a bash guard, 34:17 ratio. My chain seems to be catching/dragging somewhere as when I back pedal there is some resistance. My chain is not too tight, I've set up plenty of singles to get this part right. My bash guard was rubbing my chain slightly so I got a 4.5mm wider BB to help correct my chainline. That has not fully solved the problem and I think I will need to space the bash guard 2mm away from the chainring, this should solve the rubbing at the crank end of the equation.

I am also seeing that the freewheel seems to catch a little on each rotation as evident that the chain does a little jump while freewheeling. I have noticed a similar problem on another freewheel (AC Racing 15T) that I used on another build. When I replaced the freewheel with a no name 16T it solved the problem. My current setup has a Shimano 17T that is having the problem as well as a new AC 15T that exhibits the same behavior. I cant imagine that it could be the hub because they are both threaded on opposite sides and having the same issue. The hub spins perfect without the chain and it is brand new. Two bad Freewheels? Any ideas? Something I am missing here?

Stiff link?

I don't think you did the right thing by just tossing in a longer BB. You need to match front and rear chainlines. Do you know what they are now?

Nah, i just looked into that the other day, I'll be measuring that tonight when I get home to see whether it is off or not, up till now I have usually just eyeballed the chainline, but now that I know how to measure it I will get it exact. Luckily with a cartridge BB I can use spacers to correct the chainline without having to get a new one. It is not a stiff link either as the problem is when it freewheels not when I am pedaling. the other thing I did when i built this bike up was to flip my chainring around opposite of the correct way. I didn't think this would matter but maybe I should put it back on the right way? Are the teeth on a chainring not centered on the ring?

Some aren't. If yours are offset it will affect the chainline, though not by much.

Take off the wheel and try turning the cog by hand, like you were cracking a bank safe. Can you feel anything going on in there? Try with axial pressure.

I'll try that when I get home tonight, I'll also try flipping the CR back the other way(the rubbing on he bashguard seems like the CR and guard are too close together maybe). I keep reading about how crappy those Shimano FWs are, maybe I'll just switch to ACS Claws if the freewheel is crap.