1996 merc 7.4 gen 5 ignition problem?

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djbradenton

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I have a "96 wellcraft with a 7.4 bravo 2. Last week the boat was running fine. now it will not start for more than 30 seconds... I emptied the carb bowls (Webber) and then started it it ran for 30 seconds and stalled as if it were flooding or timing. Long story short, just put new carburator on and new plugs, (old ones one day old were fouled and black) started it up and same thing is happening. Anyone know if this is something with the knock detection or ignition control module?
 
havasuboatman

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Re: 1996 merc 7.4 gen 5 ignitionproblem?

Re: 1996 merc 7.4 gen 5 ignitionproblem?

The first place I'd check is in the new carb. are the floats correctly set? You didn't go out an buy some monster 850 carb thinking you would go faster, did you?
First tough, you need to know all your carb adjustments are correct. Make sure your water separating fuel filter isn['t full of water.
does your engine still have the clear tubing that runs from the mechanical fuel pump to the base of the carb? If so, Is there fuel in it? If yes, your fuel pump is bad.
 
Bondo

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Re: 1996 merc 7.4 gen 5 ignitionproblem?

Re: 1996 merc 7.4 gen 5 ignitionproblem?

Ayuh,...

Did you even look at the Weber,... Kitting,+ Cleaning would probably keep that Carb in service,...
Those are Fine Carbs... Easy to work on,+ tune....
Same exact thing as the Edlebrocks...
 
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djbradenton

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Re: 1996 merc 7.4 gen 5 ignition problem?

yes all was checked the webber was in very bad shape the new carb is the edelbrock replacement for the weber. every thing from the tank to the carb is all good or new. the old webber was rebuilt but it was in bad shape to begin with. Anyway every thing is new and adjusted to fact specs. I keep reading about the icm and knock control modules thinking they are advancing the timing too much?
 
Don S

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Re: 1996 merc 7.4 gen 5 ignition problem?

Have you checked your water seperating fuel filter to see if you have water in the system?
Have had many customers bring in boats with new carbs, with still the old filter full of water with very little gasoline going to the carb.
 
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djbradenton

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Re: 1996 merc 7.4 gen 5 ignition problem?

yes seperator is new also and fuel is not old the boat is used all the time. It actually coughs and spits back when trying to start it after it initially starts then boggs down after 20 to 30 seconds. then doesnt want to fire at all
 
Don S

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Re: 1996 merc 7.4 gen 5 ignition problem?

Have you checked to see if you have spark immediatly after it stops running?
 
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djbradenton

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Re: 1996 merc 7.4 gen 5 ignition problem?

No I havent , It got dark down at the boat But I will check that first thing in the am. that would tell alot right there. Thanks don
 
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djbradenton

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Re: 1996 merc 7.4 gen 5 ignition problem?

Ok after replacing everything, including the carb it needed it anyway, it turned out to be the coil itself... never thought they would work intermitently but evry other test I did pointed to it and the old big block cranked right over and runs like a charm.... Hope the coil lasts.... Thanks all!
John
 
Don S

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Re: 1996 merc 7.4 gen 5 ignition problem?

One thing that could cause coils to go bad is a bad plug wire or bad spark plug. Have you done a tuneup lately, how do the plug wires look?
 
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