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4.3 Merc wont start

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Steve Diomin

Contributing Member
Working on a a 1996 4.3 Merc on a Mariah and cant get it to start. Heres what happened:

Was out for the day on the water
Boat running fine. Turned the boat off to jump off for a swim. After the swim went to start up the boat and realized i slightly left the throttle in forward when i turned the boat off. Now with the throttle back in neutral of course i cant get the thing to fire. At first the motor wouldnt even turn over, so i thought it was the starter. After a couple bangs with the hammer and a few nights sitting i come to the boat to try to start it and it will now turn over but will not fire. There is a 1/4 tank of gas so i dont have any reason to think the boat is out of gas, plus i put in 10 gals just to make sure the boat had gas. When trying to start the boat now you get alot of vapor/cloud arising out of the carb.............not sure what this is, if it is typical or not.

The boat has had zero issues with starting or running before this. zero.

So guys, where should i start.............is there something tied directly to me turning of the boat in gear by accident that is not alowing the boat to start now???............or is that just coincidence and i have a problem elsewhere.

THanks,Steve
 
First go out and make sure the shift control is in NEUTRAL.
second spin the prop by hand (NO KEYS IN IGNITION) and make sure it is in neutral.

Now retry to start.

When trying to start in gear two things occured most likley,

one, you activated the neutral safety switch so NO turn over of the engine what so ever, (no starter at all).
two you may have activated the SHIFT INTERUPTOR SWITCH which kills the ignition when trying to shift out of gear (momentarily) but can be stuck activated when shifting from forward back to neutral with engine not running. (V notch device on engine where two shift cable attach) the switch must be in the middle of notch and not closed, this shorts coil to ground. = no ignition.

try that and report back
 
i will try this, however to test to see if the neutral safety switch was working i tried to start the boat with it in gear and nothing....no starter no nothing, so that tells me the neutral switch is working. I will look at this shift interuptor switch. you speak of.
Is the vapor coming out of the carb usual?
 
The vapor is telling me you are getting some gas to the carb.

The dead mans switch, pull it and set it a few times and crank the engine. First pump the throttle fully down and back and look at the carb the choke closed ?

Crank it if it doesn't start after 4 turns stop. Place a spare spark plug in a wire you pulled off a plug and hold it to the block and see if you have spark to the plugs post back.
 
Steve Diomin said:
At first the motor wouldnt even turn over, so i thought it was the starter. After a couple bangs with the hammer and a few nights sitting i come to the boat to try to start it and it will now turn over but will not fire.
Click to expand...
pull the spark plugs and check for signs of moisture (water) in the cylinders.

that sounds like a failing riser gasket or manifold

while you have the plugs out, compression test the engine just for reference
 
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