AMTRA.com.au

A

 The WR's do like to run lean but if it had plenty of power and it's been running this way for a while I'd guess that it's still within safe limits.
 
Lean running can cause burnt valves and in rarer cases holed pistons.
One way to see if there is a problem with the vales is by checking the clearance. A valve that is burnt will close up it's clearance as it losses material or the valve seat loses material. But there is normal wear also to consider and how long it's been since the last valve service.

Half a turn out on the idle mixture screw should add enough fuel through the whole rev range to stop it backfiring.
Was it a big backfires or a more like small pops? 

My 426 has 6300 km on it, valves checked regularly and only needed adjustment once.  I would think 3700 km is not a problem and is really a low use bike.

As for the starter motor, if you can kick it then wait till it stops working before worrying about replacment.

Just make sure it really is 3800km's lots of guys take there speedo's off...

3700 K's in 5 years is very low. I've clocked up 2000 in my first year and i don't feel like i get to ride enough. The backfiring and bogging sounds like the white bros pipe has been thrown on without the jetting adjusted to suit which may indicate that it has not been serviced by a reputable dealer as they should have picked up the telltale signs of running that lean. Easy to fix that problem though with some jetting changes or even putting in an fuel screw to richen the mix(There may already be one there).
You can also check to see if the free mods such as the airbox have been done. I may be wrong but i believe that on the 03' that some of the airbox could be cut out to increase airflow. If this has been done, have a look at the quality of the work. Another indication of dodgy work or the home handyman type of work.

Good luck.
Andrew

Go with the ones you know and trust, the Honda guys.
The difference in price for the parts will not be that much.
By the sound of it the bike is in need of a mechanic more than parts.

+1 with Tim, use the mechanic you already know and have some trust in.

So when do you take it out for the first ride?

Cheers for the advice again guys, much appreciated!

I'm keen to take it for a short trail or two tomorrow arvo, and see if I can feel anything else that I need to tweak during the scheduled tune-up next week...

Then I'm keen to get out with the AMTRA guys for some serious kick-ass trails!!

That'll probably be in 4 weeks tho cos I'm finishing my uni course then and have to write my thesis at some stage :)

Cheers.

That was adam posting by the way... He's over at my place and we're picking his bike up tomorrow morning.

Not problem Adam, see you on a ride.

Things to look for that show you that a bike has done a lot of kms.

Warn foot pegs, both on the area that you foot sits on and in the pivot.

Lots of wear of the paint on the frame, look for fresh paint.

Brake calliper mounting, they should not wriggle too much when grabbed by hand.

Disk condition, no dish where the pad runs.

The condition of the plastics, at less than 4000 km it should still look fairly good. If there are new plastics may show that the original ones were showing age.