Bike just had first service now always backfiring ( KLX)

[soundbeltfarm]

Had my KLX 300 serviced for first time last week it is new bike and changed 3 shims and done whatever else they do for a first service.
Took it on a trail ride today and when i was button off the gas it would always backfire.
what would they've done to the bike that could cause this?
and what is a general cause of back firing?
Thanks for any help

[merv]

General cause of backfiring is lean mixture on closed throttle which they may have altered by adjusting your pilot screw on the carb.

[Motu]

As Merv says,lean at idle - they would of set the idle in the workshop,on a trail ride it's going to be running much hotter and so run leaner.Just set it a tad richer.

[soundbeltfarm]

Thanks for that.
also should the shims need changing at the first service or it that the valves have just seated themselves in?

[Motu]

With modern machining tolerences valve adjustments aren't as common as they used to be,but by the first service they should of settled,maybe enough to need a shim change.

[soundbeltfarm]

With modern machining tolerences valve adjustments aren't as common as they used to be,but by the first service they should of settled,maybe enough to need a shim change.

Thanks Motu.
gee you're a wealth of knowledge.