Rough running...

[justrfb]

Hello All.
We did it!... We went out yesterday morning on our maiden voyage. Thank God we were with the mechanic from the place we bought our boat. It was rough running, well actually, it ran awesome but after a minute or two at perfect constant RPM, lets say 5800, it quickly dropped to 5K then a few seconds later 4200, then 3500... Eventually, if I didn't adjust the throttle position, it would almost get to idle. I would bring it back to idle for a few moments and could start the whole process over again. 6K doing about 22-23 MPH, after a few moments, 5200, 3500... It is a 20' Princecraft Vantage 20L with a Merc 75 HP 4 stroke hanging off the back. The mech kept it there and said they were going to look at it today. What do you think? Thank you for your help...

Sincerely,
Rich

[Ron Burgundy]

Sounds like a fuel supply issue.

[redbeard]

Bad vent can't get air to the tank.

[jrolin1]

Was the throttle actually moving? If so then there is a friction adjustment to keep it from going back down by itself. No big deal.

[kryptonite]

Sounds like a fuel supply issue.

Bad vent can't get air to the tank.

Almost has to be a fuel related issue. Like said above.

I have also seen the motor suck air from a bad primer ball. Easy way to test is to use a new hose and primer with a portable gas tank.

[justrfb]

All good points, thank you. I was thinking similar in that when the engine was at a constant RPM, it was purring right along, making me think it was most likely, not an engine issue... Boat is at the marina we bought it at so hopefully we will hear from them today. Thanks for your help.

Sincerely,
Rich