so, about 2 months ago I had my 05 FXDLi dyno tuned (fairly stock setup, no power commander or anything) and it has been running really well so I don't know if it's relevant.

In the mornings the bike starts with no problems, turns over maybe a couple of times before it catches and then runs fine. But... in the afternoon when I go to fire it up to head home it's not behaving well.

What usually happens is I'll turn the key, wait for the engine light to go out (and I can hear the fuel pump prime) but when I hit the run switch it tries to turn over (and the lights dim) but it never catches. I usually end up having to try this 5-10 times (letting it turn over 3-4 times each go) and, so far, I've been lucky and I've got it started before the battery gives out.

I've checked for codes and everything comes back as "none"

Don't know if it's relevant but I'm at work at 8am, leave around 5pm so the bike is sitting in the garage at work for less time than the garage at home. Also at work I come pretty much straight off the freeway and 3 stop lights later I'm parked but going home it's about 4 miles of fairly slow surface streets before I park up.

Any suggestions on things I could look at (not very mechanically minded - I can spray WD-40 and did manage to change the spark plugs on a car once so be gentle!) or should I just head back to the folks who serviced it?