wr450 flat spot help

[TnN]

hi guys ive just purchased a wr450f 2003. when i got it home it was leaking oil on the right hand radiator and after some research found it was missing the decomp plug so i sorted that. when trying to start it after a few days of sitting it will crank and every third or so crank will pop from the exhaust until it starts. once started and warmed up it has a flat spot when trying to accelerate down low and sputters. if i quickly flick the choke on it rides perfect other then high idle. i changed the spark plug but the issue is still there. im hopeing for an easy fix and some advice.i can do basic stuff like removing and cleaning the carby if need be. i was told it wasnt ridden for a month or so when i purchased it so maybe a carby/fuel issue? thanks in advance

[FORMA MOTO]

Pretty normal for a bike if it sits too long.

 

Pull the float bowl cover and inspect for any white, brown, or green corrosion.

 

White is water, brown is old fuel, and green is ethanol and water.

 

At the very least you will need to replace the pilot jet and spark plug, and do a vavle clearance adjustment.

 

These bikes come set up very poorly from the factory, and if you want it to run smooth and consistently, you will need to do some reading up on the uncorking and rejetting, and possibly the dissconnection of your TPS and ACV systems.

[TnN]

im concerned about the pop/backfiring when cranking it to start it