Engine starting, but failing to idle, carb spits vaporized fuel upon stall

[jrkrohn]

HELP!!!!
Here's the story. I have a 1995 Sea Ray 370 Sundancer with carburated 7.4 BlueWaters(454's). A couple weeks ago I started experiencing rough idle, acceleration, eventually leading over time that the port engine just wont idle anymore. I replaced the spark plugs, coil, cap, rotor, carburator (installed EdelBrock 1411 750CFM to match the Weber on starboard engine) - since the original Weber was still leaking after rebuild. I have also replaced fuel/water filters as well. The starboard engine runs absolutely fine on either tank, so we know its not bad fuel. I can get the engine to start, but it will spit vaporized fuel back out the carburator upon the time it stalls. Any ideas? It has been suggested that it's the ignition control module attached to the distributor, since it's acting like a timing issue. The timing has not been adjusted, nor is the distributor loose. Has anyone seen this issue before? Please get back to me asap with ideas. I need to have this boat running by Friday since I have guests coming from other parts of the country... Any help will be greatly appreciated!

 

[Quint4]

A few quick thoughts:
- What about the fuel pump.....mechanical? Is there fuel in the sight tube (should not be....ruptured diaphragm).
- Get a timing light and check the timing.
- unseated or crossed plug wire? ( I doubt it)
- possibly ignition sensor in distributor as you mentioned

 

[Happy Hour IV]

or a stuck open valve. Is this particular engine/hull combination on the known water reversion problem mercruiser has ? Time for a quick compression check. You could lift the spark plug wires one at a time to isolate a bad cylinder.

 

[PlayDate]

Since time is short.....I'm going to start with a huge assumption: The problem you are having now is the same as you had when you started working on the engine.

That means the new parts have not addressed the problem. Happy Hour/ Quint 4 get my vote for suggesting the fastest way to sort this out. I would check the fuel pressure at the carb and the compression of the cylinders. I know it is a pain to check cylinder compression but if it isn't the fuel pressure the last mechanical process to rule out is compression. I hope it is fuel pressure because the alternative is a bad weekend.

If the compression is fine and the fuel pressure is good .....the only thing left is the ignition system. Generally speaking when the ignition control module goes bad .....the engine won't start. When I first read your post....I suspected crossed-ignition wires (your can recheck the firing order when you do the compression test) but that is why I started with the assumption that you haven't found the problem yet.

-John

 

[Happy Hour IV]

There are two components to the ignition system. The visible one is the module mounted on the side of the exhaust riser. Very expensive.
Mine are original from 1988. The other is the sensor in the distributor. Mine have both been replaced. When they failed, the engines started
but ran like a bag of c..p. I think John is referring to the module and Quint is referring to the sensor. I am not sure how to properly test the sensor but mine were visibly bad. The little capacitors on the sensor had ruptured. Hopefully a compression check is OK and that it is just this sensor. I think the sensor may also be called a "pick up". My guess is still the valve. let us know what you find.