Merc 5.0 Stalls when coming off plane

[familymanbob]

My dad has a 1995 MAXUM 26' cruiser with a merc 5.0 (which is WAY TOO SMALL OF AN ENGINE). It has the stock 2 BBL carb. I am trying to help him figure out why it seems to die every time he brings it off plane. I've ruled out (I think) the shift interrupter because it will go from low speeds into neutral properly and provide the momentary pause to the engine.

In order to restart the boat, he has to put the throttle all the way open and crank for about 30 seconds straight to start the engine. Almost seems like a float or flooding issue to me. The carb was rebuilt last year by another guy at the dock as a result of the problem with the stall that he was experiencing, but the only thing I see from that is it seems to be running rich right now as well.

Can you provide me with a few areas to check? Thank You!

 

[ktbarrentine]

Re: Merc 5.0 Stalls when coming off plane

Have you checked the fuel pump sight flow tube?

 

[cr2k]

Re: Merc 5.0 Stalls when coming off plane

Float level? Water in tank? Low Fuel Level? Water in carb?

 

[kylejb2663]

Re: Merc 5.0 Stalls when coming off plane

Very interesting post!!! Mine is doing the same thing except it's when I'm shifting a lot (like docking). I was told to rebuild both carbs and put new ethanol floats in- Going to try it this weekend possibly if I get all the parts together-

 

[familymanbob]

Re: Merc 5.0 Stalls when coming off plane

Thank you, I will check these items out. I will let you know what I find. I have no idea what the fuel pump sight flow tube is, but I suppose I am getting ready to learn everything there is to know about them. Thanks Again!

 

[ktbarrentine]

Re: Merc 5.0 Stalls when coming off plane

Sight flow tube comes off fuel pump above diaphragm and goes to air horn of carb. If the diaphragm in the fuel pump starts to crack/fail (and they are doing that these day because of ethanol gas and age), it directs fuel to the carb instead of into the oilpan of the engine. This extra fuel going into the carb will cause a flooded symptom. Happened to me on 1990 5.0L. It's just an easy thing to check and rule out when the engine is running. Should see no fuel in the line going to the carb. (If yours is like mine, it is very discolored by age. I replaced mine recently when I replaced the faulty fuel pump).

 

[familymanbob]

Re: Merc 5.0 Stalls when coming off plane

Hey guys and gals, I am back from vacation, so here is what I found just before heading out:

fuel pump sight flow tube - seems to be ok, no visible fuel, and used a pair of vice grips to gently plug the hose so that no fuel could flow - no change
Water in tank? - Added dry gas (enough for full tank). Dad is really good about this anyway
Low Fuel Level? - Full tank of fuel
Water in carb? Wouldn't the dry gas take care of this one?

Float level? looks like I may need to take the carb apart to try replacing the float? The carb was rebuilt last year (fall) because of this problem. However I will say that last weekend, I spent several hours troubleshooting a solenoid that was bad out of the box

 

[ENSIGN]

Re: Merc 5.0 Stalls when coming off plane

Remove the water separating filter and empty it's contents in a clear jar.See if any water is at the bottom'if so you have water in the tank and it must be pumped out.Dry gas will not remove it and will only attract more moisture.

 

[familymanbob]

Re: Merc 5.0 Stalls when coming off plane

Thanks. I just went down and did just that. I fully expected to see water as this is similar to what happened with the diesel farm tractor recently. Not really even a drop of water.

thanks!

 

[scoflaw]

Re: Merc 5.0 Stalls when coming off plane

Exhaust shutters. The ingested water is putting the fire out.

 

[familymanbob]

Re: Merc 5.0 Stalls when coming off plane

Exhaust shutters. The ingested water is putting the fire out.

Interesting thought. I will check. Thanks.

 

[gmredline]

Re: Merc 5.0 Stalls when coming off plane

Sight flow tube comes off fuel pump above diaphragm and goes to air horn of carb.

What do you guys use to replace that hose?

Mine was completely deteriorated and cracked in several places. The line was tinted blue and black and I never knew it was supposed to be clear. Since the line ran from the fuel pump to the carb, I replaced it with some fuel line from Goodyear which is black. Come to find out, that defeats the purpose of the Sight Tube...

 

[ktbarrentine]

Re: Merc 5.0 Stalls when coming off plane

What do you guys use to replace that hose?

Mine was completely deteriorated and cracked in several places. The line was tinted blue and black and I never knew it was supposed to be clear. Since the line ran from the fuel pump to the carb, I replaced it with some fuel line from Goodyear which is black. Come to find out, that defeats the purpose of the Sight Tube...

Mercruiser parts websites carry that tubing. Pretty standard in length (maybe a little long so you are able to cut-to-suit). Costs about 22 bucks, but is the required replacement. You are right, black, although it will serve the purpose of directing fuel from above the diaphragm to the carb (to keep it from going to the oil pan), you cant see it when your diaphragm fails (like mine did). The replacement tube is the "right" material for this application. DO NOT use tygon or vinyl tubing (i.e. aquarium tubing, or the stuff you can get at Lowes or Home Depot). It is not rated for the job.

Try these sites for examples and places to order:
www.mercruiserparts.com
www.crowleymarine.com

Mine is this part number: Part Numbers : 7381567, 32-7381567, 327381567

Good luck. (and you really should start a new thread for questions like these, and not hijack the thread.)...HTH! KTB.

 

[gmredline]

Re: Merc 5.0 Stalls when coming off plane

Try these sites for examples and places to order:
www.mercruiserparts.com
www.crowleymarine.com

Mine is this part number: Part Numbers : 7381567, 32-7381567, 327381567

Good luck. (and you really should start a new thread for questions like these, and not hijack the thread.)...HTH! KTB.

Thanks for the info.