In my opinion Pit stop should take 5-7 seconds by good mechanic with gun.
Till 10 seconds by less experienced man.
Fuel gun make difference, you can be sure that you have 75ccm in the fuel tank not less. Sometimes, when mechanic desqueeze the bootle too early it pumps fuel OUT of tank... I had one situation like that... It sucks...
But you must know, that fuel always spills a little bit.
By the way I have tested a lot of guns, (RB, Xceed, Proline, Ofna) and Xceed seems to be the best so far.