Shift Interuptor Switch Causing cut out?

[tu1aher1]

Hello All,


I have a 1985 Mercruiser 140 3.0 stearndrive in a 1984 Hammond pleasure boat runabout.

I took the boat out this last weekend for the over night fishing trip I with a couple of my buddies. Every thing went fine the whole night. We fished in several different spots stopping then going to other places. A while after the sun came up the boat started having the same old problem it had in the past. We were putting along about 25mph then all the sudden the engine would die. I put it in neutral with a little throttle and the boat would start up again just fine but as soon as I came back to idle and put it in gear, give it gas it would die. I noticed there is a slight hesitation right when I push the throttle forward then under normal operation the engine would get past the hesitation and rev up. I'm assuming this is the Shift Interrupter at work? The hesitation I mean? But now when this problem started to happen on the lake, when I pushed forward on the throttle, going in gear, the engine would encounter the hesitation but not make it over or "catch up" and just die and it got progressively worse. At first when it died going at cruse speed I could put it in idle and start it up again, put it in gear and get it passed the hesitation and then it would take off like doing a wheelie because of the throttle being so forward but eventually it would die again at cruse. Eventually stuck in the middle of the lake I would start the engine again in idle, which would start up fine, and push the throttle forward in gear with a load on the propeller it would die. It would run great when in neutral and I could rev it up as high as I wanted it to go.
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I am completely baffled. the two problems:

1. Why did it eventually start dying at cruise speed?

2. Why is it dying at rest when I put a load on the propeller?

Are the problems connected? It seems like they are. Is this a bad Shift Interrupter Switch?





I verified the carb is getting gas. I tried to make some adjustments to the idle you name it, nothing. It is either electrical or carb as much as I can tell. I thought maybe the coil is getting too hot but I come to find out this is normal. I even took it out and cooled in down in a lake water being careful only to put the bottom in the water. I had it nice and cool but still did not fix the issue. I eventually got a tow back to the ramp.

I very much appreciate any insight that any one could give me for this very elusive problem.

Thank you guys.

 

[Bt Doctur]

sounds like more of a carb problem,
Watch the shift interupter as you shift into gear, if it moves the lower shift cable is bad. Should only move coming out of gear, in the water, with a load on the prop.

 

[Fishermark]

Simple way to check is to visually look at the shift interrupt switch to see if it is engaging when you shift into gear. It should not. It should ONLY engage when shifting OUT of gear - and then only briefly. If it is engaging when going into gear, then you either have a bad shift cable or an incorrectly adjusted shift cable. With the boat in the water, open your doghouse and look at the shift mechanism while someone else shifts.

 

[tu1aher1]

Thank you guys. I will check this and see what happens.

 

[tu1aher1]

I started reading around and it sounds like there could be a accelerator pump that is bad. Can this be replaced or adjusted or would it be worth buying a new or rebuilt carb? I had the carb rebuilt about this time last year. Should that have fixed any accelerator pump problems in the carb or is it possible to rebuild a carb and it still have an acceleration pump problem? Thanks a lot for all your input!

 

[thumpar]

The carb rebuild kit will include the accelerator pump. An easy way to check is to look down the throat of the carb while someone pushes the throttle forward. If you get a squit of fuel it is working.

 

[JerryIrons]

It should be a healthy squirt as well. If you can slowly ease the throttle up to speed just fine, that's another sign of a bad accelerator pump. Check both your fuel filters as well.

Had to laugh at your "putting along at 25 mph"...

 

[achris]

First thing I noticed is that it's getting worse. And a hesitation as you accelerate. First thought - fuel tank vent. Check it (the vent or it's hose) is not plugged or restricted in any way. But if you suspect the shift interrupt, as everybody else is saying, it should NOT move when going into gear, or accelerating, ONLY when coming out of gear with load on the propeller. That means it will not activate when you are running the engine on flushers, or if you pop it out of gear as the boat is slowing down (prop is being driven by the water rather than under load from the engine. Like a car 'overrunning' down a hill)... What you should see, if you're quick enough, is the tacho just dip for a fraction of a second as you pull out of gear. That'll tell you the switch is working.

Chris....