weird problem with 3.0l merc

[sneakypete]

OK so my boat is running great after new plugs and dist cap and so forth. Im getting actually 200 more rpm's then last year, and im actually topping out near factory spec. However after I run the boat at cruise or WOT it runs great until I back it down to just the point where it is in gear. At this point it bogs down to 400 rpm's then dies. I fire it right back up and it works fine. It only stalls when you bring it down from a high rpm. I can put around all day but once I run it an bring it back to 800-1000 rpm it wants to die. Last seasons gas is still in the tank, it is a carburated engine. Im thinking bad gas or a carb that is on its way to a rebuild. It is a 2005 with about 150 hours, just put on fuel/water sep this year. Any suggestions?

[165Striper]

The first thing I would check is the new fuel/water separator and any connections you made in the fuel line. It sounds like you might have a small air leak.

[sneakypete]

The first thing I would check is the new fuel/water separator and any connections you made in the fuel line. It sounds like you might have a small air leak.

Good point. I will check the lines and make sure it is all tight. I had to put the seperator on the opposite side of the bildge from the fuel pump. Wasnt much room for me to work with.

[sneakypete]

Good point. I will check the lines and make sure it is all tight. I had to put the seperator on the opposite side of the bildge from the fuel pump. Wasnt much room for me to work with.

If that is true I would like to know why nothing is effected by the vacumn leak at top end.

[midway]

If you were sucking air you should have wot problems as well. I don't think the carb is the problem, there may be a little water that causes the shutdown but then it would seem that it would not putt around as you say. I would check the kill switch on the engine that works when you shift in and out of gear, there could be drag in the cable that is making the switch try to work.

[sneakypete]

If you were sucking air you should have wot problems as well. I don't think the carb is the problem, there may be a little water that causes the shutdown but then it would seem that it would not putt around as you say. I would check the kill switch on the engine that works when you shift in and out of gear, there could be drag in the cable that is making the switch try to work.

Well I can putt around for a little then when I get back to dock and throw it into reverse it finally stalls. It chugs along at idle but eventually dies. I will also check the kill switch. I tried raising the idle but that didnt do anything. Id also like to mention I did use fuel stabilizer but I left the tank half empty. Has anyone used sea-foam...should I use it. I am going to burn as much fuel as I can then replace it along with a new fuel sep. Yea I agree about the carb its only a 2005 with under 200 hours. I dont think the ethanol ruined it just yet.

[midway]

I use Seafoam, just put a can in my tank before I went on a recent trip to central Fl, it is good stuff.

[Chief Alen]

Rebuild the carb it's gunked up.

[165Striper]

If that is true I would like to know why nothing is effected by the vacumn leak at top end.

I don't have an actual answer, but a guess. I had a similar problem on my outboard that turned out to be a leak in my water separator housing (at least that is my guess). The boat would start fine, idle fine, run WOT fine, but would stall out when brought back down to an idle after running for a while. My best guess is that I had a VERY small air leak that under light loads didn't leak, but after running at higher rpms would introduce enough air into the line to make it hard for the fuel pump to feed the motor at low rpms but could still suck fuel around the air at higher rpms (kind of like a poorly primed siphon). I never had a fuel leak, but after replacing fuel lines and filters (along with other stuff!), I replaced the housing in an act of desperation and my problem went away. Like I said, it is just a guess. I really have no idea, but it fixed my problem.

[Beaubeau]

Pete, Was there a filter that you had replaced that was in the carb?

If so, a common problem with the symptoms you have is a piece of crud keeping the needle and seat in the float bowl from closing.

The way to check is to look down the carb when it is running in the idle position. No fuel should be comming out of the main jets in the airhorn.

The correction is to starve the carb out of fuel when running by squeezing off a rubberline between the fuel pump and carb. Before it totally dies out, unclamp the fuel line and a burst of fuel will blow the debri off of the needle and seat.

If this desn't help you, I hope it can help someone else.