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05xsvego

5.7 Mercruiser stalling out and dying

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I am relatively new to boating and have been working on my first boat for about a year. 

It is a 1988 2350SX that required a lot of TLC and as always some much needed repair.  I ended up re-powering with a slightly newer used 5.7 alpha one setup with 120 hours on it that came from the great lakes area.

On the trailer the engine fires up and runs flawlessly.  The only thing I did to the replacement engine was had the carb rebuilt . 

I put it in the water for the second time now and have had the same problem both times.  I get the boat in the water, run the blowers for 4 to 5 minuets and the engine fires right up. I stay at the dock with the engine running and let everything warm up (160 to 175 degrees).  It takes a few minuets but everything runs normal.  

After everything is warmed up I am able to put it in reverse and pull away from the dock.  I am able to shift into forward and start heading out to the Chesapeake Bay.  After running out at about 5 MPH I notice the engine starts to loose a bit of power intermittently and the picks back up.  After this happens a few times it will loose power and eventually stall out. I can give it a little gas and the engine will restart and I can get moving for a nit and the engine repeats this again and again.  

I tried increasing the throttle only and let it run at a higher RPM for a little bit and then go into gear but it does the same thing. 

Last night when this happened It seemed to clear up as I got close to the dock and I was able to go into gear both forward and reverse and pull right up no problems.  I left the engine running at idle for about 10 minuets and ran smooth with no problems. I

It has me at a loss as to what the problem could be. 

At idle I am sitting at about 750 RPM and it holds there with no issues

Engine temp last night was 170 degrees 

Things I have done before putting it in the water 

New Plugs, D-Cap, Rotor, Wires and a new fuel water separator. 

I drained the fuel tank and filled it with about 40 gallons of 89 octane and a little less than 4 oz of Stabilizer (Sta-Bil marine) 

I cant help but think I am having some sort of fuel problem.  My first though is that the mixture is to rich basically flooding it out when i get going. 

There is no smoke form the exhaust and the engine idles smooth with little to no vibration. 

 

Any help or advice on what may be causing this would be greatly appreciated

 

Chris 

 

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I agree that you have a fuel delivery issue, and the reason it runs in the driveway is that you have zero load on the engine and are requiring a lot less fuel. You can rig a temporary fuel pressure gauge in the fuel delivery line and watch for a minimum of 6 psi, but there is also a fuel inlet screen on the carb at the fuel inlet that I would check first. Also, check the anti-siphon valve at the fuel tank as they get plugged up once and a while. Beyond that, fuel filter and/or fuel pump. I do not think you have any issue with running rich as the jets are fixed and that condition would show up at idle if the carb float was saturated or there was something stuck in the needle and seat. The mixture screws are for idle mixture only as they are out of the game as soon as the throttle plate is advanced above idle speed. You can look down the venturi  during operation to spot an over-fuel condition but I'm thinking that is a waste of time. Start at the little carb fitter, then go to the anti siphon valve.   W

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Thanks for the quick reply. 

That's what I will check first and foremost.  

I am thinking it is something simple,  I am have a lot to learn and have no problems asking for help. 

I appreciate it Wingnut,  

 

thanks again

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5 minutes ago, 05xsvego said:

Thanks for the quick reply. 

That's what I will check first and foremost.  

I am thinking it is something simple,  I am have a lot to learn and have no problems asking for help. 

I appreciate it Wingnut,  

 

thanks again

Not sure what carb you have as the 5.7's have 3 options but the filters are similar. Item two per attachment. Items 2 & 4 below. Weber does not use them.

http://www.marinepartsplus.com/catalog/mercruiser/serial/5.7L_2_BBL._GM_350_V-8_1988-1995/816596/1014-140

http://www.marinepartsplus.com/catalog/mercruiser/serial/5.7L_2_BBL._GM_350_V-8_1988-1995/816596/1014-180

http://www.marinepartsplus.com/catalog/mercruiser/serial/5.7L_2_BBL._GM_350_V-8_1988-1995/816596/1014-160    None

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While doing all of that, replace the rubber fuel line from the tank to the engine.  I had an issue a couple years ago and turned out to be that any load on the engine would cause the rubber fuel line to close off like a straw.  End of my fuel problems and an inexpensive fix.  My boat is a 1996 so the age of your fuel line is about the same as when I was having issues. 

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That is  worth a shot.  That was the only fuel line that I did not replace when I was doing the re-power.

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I had this stalling and hard starting issue on my last boat. After rebuilding the carb, it turned out to be a mechanical fuel pump issue. Wingnut's test should show you if that is the problem. I just replaced it and it worked.

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The electric fuel pump on my current boat was weak. It would usually deliver enough fuel, but not always, and would sometimes show the same symptoms. Even when it ran right at lower loads, it would starve out at full throttle and bog/surge. I got a universal electric high volume marine pump from Summit Racing and it has worked like a champ.  Not sure if your boat has the electric or mechanical pump like Drew's had, but in any case, it sounds like the same basic problem.

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I just want to say thanks to everyone who took the time to give advice on my problem. 

First this I did was to install a fuel pressure gauge on it and the mechanical pump was delivering 5.5 psi +/- .1 as it was running. 

I replaced the fuel line form the tank with new fuel line just to eliminate it as a possible cause. 

Working on it on the trailer it finally got to the point where it would run for a few minuets then stall,  eventually getting to the point where it would not start. 

I pumped out some fuel from the tank to make sure it was not contaminated.  It was not.

I unhooked the tank vent line to make sure it was not clogged or restricted causing a problem. 

Finally this morning I replaced the fuel strainer on my carb "Quadrajet".  When I pulled it out it became apparent that it was full of some crud that basically looked like wet saw dust. I put a new one in and hooked everything back up. 

I am happy to say that it fired right up and is still running great, actually running smoother than before.  I reset the idle to 800 RPM running on the muffs and hope i can get it out on the water today to see if the problem is eliminated.

 

Once Again,  I cant thank all who replied enough for there help on this. 

Thanks again 


Chris 

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I remember us teenage hop up artists. The first we removed was the carb inlet air & fuel  filter.  TOO MUCH restriction to go fast.   Now we know better.  :angry:

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I couldn't have given better advice as these guys were right on.

Wouldn't be a bit surprised if the "sawdust" in the carb filter was fuel line residual and replacing the fuel hose will probably eliminate future plugs.

Good luck.

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I had black sawdust in a very seldom used large weedwacker carb also. Forgot to drain the tank. I slit open the fuel line.  Crumbly insides.

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  We had a 1950s ?  Racing hydroplane. Those big round nosed boats with a huge original Chrysler Hemi engine in it.  The engine would start & go slowly to the race course fine. 1 to 1 1/2 minutes at WOT slow down & die.  I asked the owner if he restored the fuel tank like the rest of the boat.  NO  Would you get it removed & cleaned ?  NO 

After 2 more trips out. The great mechanic & I held the owners head underwater until he agreed to send the tank out for a spotless inside. When everything else is checked 3 times & only 1     KNOWN   item was left in a field for ???? years UNCOVERED.   DUUHH what part should be restored also.

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Cyclops, What a coincidence ! We raced a Hemi powered hydro with the big round nose in the Gran Prix class. Back to the subject. I also experienced the white stuff in the fuel line from a "Before Ethanol" fuel system. The Inside of the hose peeled out like spaghetti.

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