I've got a Mercury XRi EFI 175 on a Ranger 481vs. Serial is 0D123631. It starts up at the beginning of the day relatively easily (sometimes requires advancing the throttle a little), but as soon as I go to take off it hesitates and sort of bogs down for 10-15 seconds before finally taking off and getting on plane producing a fair amount of extra smoke in the process of getting going. For every subsequent takeoff throughout the day it jumps up on plane without issue, even if I let off of it as soon as it gets on plane the first time to try again. It's almost like it's got something that builds up when it sits that it has to "blow out" by making it through a takeoff before running right. It's done this for as long as I've owned it, but it's something I'd definitely like to get figured out!
Spark plugs are probably 2 months old and the problem has persisted over several sets of plugs, compression (as read by a Harbor Freight gauge) is 118-120 across all 6 cylinders, fuel lines from the tank to the motor have been replaced within the last year or so, primer bulb was replaced at about the same time, pulse fuel pump was rebuilt at the same time (admittedly due for it again, but it had the issue before rebuilding it), fuel filter (fuel/water separator) is new. I always pump the primer bulb firm before starting.
After looking through a manual for the motor, my initial thought was that the issue was related to the exhaust relief ports on the back of the motor being submerged when the motor is trimmed all the way down, but it would seem that this issue would remain throughout the day and not just the first takeoff of the day. Is it possible that the exhaust relief ports being submerged could only cause the motor to struggle first thing in the morning? I do have a jackplate I need to get around to installing that would likely solve that problem or at least rule it out. I've also tried the technique of beginning to take off with the motor trimmed higher then trimming down as the boat begins to clear the water a little. There have been times it seems like it helps, while others it seems like it does not.
The problem also seems to be worse if I let the motor warm up/idle longer before taking off. Idling before taking off for short or long periods later in the day doesn't affect it.
This one really has me stumped. The behavior of only doing it the first takeoff of the day then working wonderfully after that is the strangest part for me.
Thanks for any guidance you all can offer!