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Old 04-21-2011, 06:10 PM   #1
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Default Merc 5.7 Stalls @ 3000 RPM

I have a '98 2352 MH w/ 5.7 Merc. It stalls consistently at 3000 RPM. Any ideas?
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Old 04-21-2011, 07:28 PM   #2
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gotta give us more than just stalls dude....
first off..welcome to the zoo...2nd does it fire right up again??,....more details please??...


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Old 04-22-2011, 01:33 PM   #3
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First this is just over 8 knots, at 2800 rpm engine noise will noticeably change, if i bring down the throttle it won't stall, if i leave it it stalls but will restart, it's consistent 8-10 knots, 3000rpm, additionaly it has the se116 drive. i'm going to change out all fluids/liquids, but i'm guessing it doesn't end there as it already starts/runs, i'm wondering if this is a drive issue or an engine component in need of replacement, getting thru the 895 page manual is a process....
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Old 04-22-2011, 02:43 PM   #4
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Have you tried cleaning the carb? clogged up jets could lead to such a condition. Choke sticking could as well, I would think. Bad fuel might, but I'd think that would be running rough and even possibly hard starting as well and would be noticable regardless of engine rpm's. Just a coouple of random thoughts.
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Old 04-22-2011, 03:57 PM   #5
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carb is one....
since we can rule out timming....I'd look at fuel filters and the vent tube....if you get to that point ...here's a quick and easy way to check....run the boat .....have someone on the back near the fuel filler cap.....be careful since the fuel filler maybe in a place that one may be in danger of falling out....
take off with the boat and when it starts to stall..have that person break the cap loose so that air can flow....he might hear a hissing sound when it releases vacuum....the engine should take off and you may see that you have a blocked vent line .....

also check the mountings on the carb...if the bolts and screws loosen up..you will get a vacuum leak...easiest way to check is use soapy water in a spray bottle...shoot the base with a stream and if the engine smooths out...voila...loose gasket/carb.....

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Old 04-22-2011, 03:59 PM   #6
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also...this isn't a drive issue...this is either carb or engine issue..stalling is indicative of fuel delivery problems....

usually!! that is..
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Old 04-22-2011, 04:46 PM   #7
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Great. W/e project. i'll let ya know how it went come monday.
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Old 04-22-2011, 06:19 PM   #8
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Definitely sounds exactly like a fuel delivery issue. At lower RPM's the delivery system is supplying just enough gas, but as RPM increases the engine needs more but the delivery can't keep up with demand and the carb basically runs dry. The different sound you notice is more than likely the engine going lean as the carb runs out.

The actual problem could be many things as Seapuppy and Shrew noted above so try the easy to check things first. Clogged vent (if you can run the boat with the gas cap off and not spill any gas into the water give that a shot) and clogged filter(s) is what I'd check first.

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Old 05-07-2011, 03:31 AM   #9
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Right you all were. Taking the gas cap off worked. How can I pinpoint the presumed clog? (i went ahead and changed the fuel filter and a fuel line. i'm not doing well navigating the engine compartment, (how the hell is anybody supposed to work on a boat engine???)

On another note i found oil in the coolant reservoir, which to me means one thing, but temp has been running fine though i had to put in two quarts also presumably covering spillage/leakage to the bilge. do i have a blown head gasket and another leak, or just the former, or am i just putting coolant in the wrong reservoir.....
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Old 05-07-2011, 09:31 PM   #10
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um.....first off....lets fix the vent problem..the tank has a vent tube that goes from the tank to the side of the boat's hull....usually on the stbd side..

you probably need to replace that entire run as it probably has a mud dobber or some other type of nesting blockage..

now for the oil problem....you have a serious problem....you should not be putting engine oil into any reservoir.....but if your getting oil into the reservoir..then you have either a cracked head gasket..cracked head....or some other item that is causing oil to leak into the water jacket....so....take the boat to a qualified merc mechanic and have him diagnose the problem...

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Old 05-07-2011, 11:50 PM   #11
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Too late seapuppy, I already took apart the engine, the gaskets are intact, though the build up around the seals was horrible, moisture and "mayonnaise" everywhere, other than that everything looks ok on the surface, the closed coolant system is in desperate need of a flush, i brought all the parts in for a thorough clean, and i plan on switching out all the components, i'm going to continue to strip it down and see if anything sticks out,
i think after some tlc she'll be in tip-top shape,


thanks for the tip on the vent, i'll pull it out tomorrow and see what's in there,

as for a mechanic, no way! i got the boat to learn and have a project (although i'm not sure i knew i was getting into a project of this size....
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