mercruiser 120 runs great for about an hour then stalls

[adam003]

i have a 1984 18.5 seray seville have owned this boat for 3 years it has a 120 mercruiser with an alpha 1 outdrive. this boat will run like brand new for and hour or so then it stalls. i can feather the throttle and keep it running but if i shut it off it has to sit for about an hour and a half or so then starts up like nothing is wrong.boat has new batteries,carb was just rebuilt,has new alternator, it has spark, changed all fuel filters and checked lines dont really know where to go from here. PLEASE help wanna get kids out at least one more time before it gets cold thanks adam.

 

[boattoy]

Re: mercruiser 120 runs great for about an hour then stalls

sounds either electrical like a coil is heating up and failing.

It could also be fuel related and be having the same problem im having. Fuel pump works for a while then starts to fail at random.

 

[adam003]

Re: mercruiser 120 runs great for about an hour then stalls

i will check the coil today and get back thanks.

 

[Don S]

Re: mercruiser 120 runs great for about an hour then stalls

Doesn't sound electrical at all, more like it's running out of gas. Possibly the tank vent plugged up and it takes an hour to build up enough vacuum the fuel pump can't overcome it.
You can try removing the fill cap and listen for air sucking in, but it's better to do this fuel system test to find the real cause.

http://forums.iboats.com/showthread.php?t=167561

 

[adam003]

Re: mercruiser 120 runs great for about an hour then stalls

went out today started right up let it run til it started to bog down shut it down and no restart. coil is still getting good spark, i think don s is right its like it is running out of gas it has a mechanical fuel pump and maybe iam wrong about it but if a mechaical fails it wouldnt run at all would it?i will check out that fuel system check link and see where iam at thanks.

 

[adam003]

Re: mercruiser 120 runs great for about an hour then stalls

checked the overflow line and blew it out just to be sure could a mechanical fuel pump fail after running for a while i know electric ones can heat up and cut out?gonna try replacing the fuel lines mine are rubber up to the fuel pump maybe one is getting hot and collapsing?also gonna remove the metal one from the carb to the fuel pump and clean it out?

 

[CoKid]

Re: mercruiser 120 runs great for about an hour then stalls

Let me know what you find. have a 1988 Sea Ray 4.3 liter. Has been doing the same almost since new. Replaced everything but carb and fuel pump. Gets fuel and spark. Sometimes looks like too much fuel. I was wondering about float setting but can't find specs. Problem has only gotten worse over time. /I]

 

[just add water again]

Re: mercruiser 120 runs great for about an hour then stalls

a marine fuel pump has 2 diaphrams in them when they fail they can still pump fuel but it will pump extra fuel thru the clear or yellow line that feeds to the top of carb which wiil add to much fuel and cause too flood carb and it will die

 

[FreeBeeTony]

Re: mercruiser 120 runs great for about an hour then stalls

Next time it stalls, remove the fuel fill cap and listen for air sucking in as Don suggested.........or, just try running it with the cap removed and see if the problem goes away.

 

[NetDoc]

Re: mercruiser 120 runs great for about an hour then stalls

Sounds fuel related to me as well. On a car, I would be suggesting that you check the exhaust as well: sound's like a clogged cat!

Personally, I would do a volume test on your fuel pump. Either it's not letting the fuel get to it, or it has become weak with age.

 

[dollarten]

Re: mercruiser 120 runs great for about an hour then stalls

Sounds fuel related to me as well. On a car, I would be suggesting that you check the exhaust as well: sound's like a clogged cat!

Personally, I would do a volume test on your fuel pump. Either it's not letting the fuel get to it, or it has become weak with age.

Take off the air silencer when it quits next time and see if gas is squirting into the carb with someone pumping the throttle a few times . If there is ,you can rule out fuel problems

 

[thumpar]

Re: mercruiser 120 runs great for about an hour then stalls

Take off the air silencer when it quits next time and see if gas is squirting into the carb with someone pumping the throttle a few times . If there is ,you can rule out fuel problems

Not totally. That only shows the bowl has fuel.