Re: mercury 7.5 carb
Can't tell if that's the same diagram as
this one but it's #8 on this one(pretty sure they're the same)... Mine has the same line running from the back of the carb to the #8 on the block....I assumed it was a vacuum line on mine ?
If yours is only 3" long I assume it's not connected on the other end, which would mean it's probably sucking air... you can see from the 2 links we gave you(pretty sure they are the same part) where it goes, there should be a check valve\90 elbow coming out of the block on the left side of the motor if your looking at it from the front, it should connect to there.