Delica Canada | Mitsubishi Van Club

Now that i say the Deli is running well i have a small little cough when its warming up, when i have the RPMs set at 1300 it lets out a little cough. it idles smooth then for about 2min of warming up ,once and a while it does it. not sure how to explain it almost like a extra little bit of fuel to choke it, then a small puff of black smoke to fallow. Iv done the fuel filter, and put in cleaner for the injectors i havent had them checked or timed. could they need setting,or the pump need a look over. The reason i havnt had them looked at is because of the price i was given just to inspect them. suggestions please if you may. and maybe some prices and places to have honest work done.
Thanks rdub