Sudden Shutdown

[jkenan]

I've read all the posts about engine shutdowns in an effort to trouble shoot the shutdowns I've recently begun to experience, and feel mine are sufficiently different to warrent bringing them up here... so here goes:

I have recently been experiencing sudden engine shutdowns (flip of a switch type) that ONLY occur when I am motoring in choppy water with the boat pitching around. Immediately afterwards, I can restart the engine and it runs fine, but the problem repeats if I'm in choppy water. In calm, flat water, there are no shutdowns and it runs fine for an indefinite period. Prior to the shutdown, there is nothing to indicate an impending problem. Engine runs smoothly at 140 degrees, no smoke, no odd sounds. I can't find anything in the carburater that would block the needle valve (had that problem before), so I don't think it is that. I have not yet tried the jumper wires from the positive terminal on the alternater to the coil & fuel pump, but will attempt that this weekend. The only thing I can come up with right now is a short somewhere that occurs with the pitching/pounding of the boat, and my hope is that testing around with the jumpers will help me isolate the problem.

In April and May, I installed a new carburator, coil, electric ignition, ignition switch, alternator, distributor cap, rotor, wires, and plugs, among other things. It has run fine until now, and I've motored in some heavy stuff since doing all of this work. This problem has just surfaced.

Any ideas?

Thanks in advance.

John

[Don Moyer]

John,

We recently prepared this little checklist of things to check on engines that fail to start. If your engine fails to start after a choppy water shutdown long enough to perform a few checks, you might try to go through this little check list:

QUICK CHECKS FOR NONE STARTING ENGINES:

Two preliminary items:

1) Close raw water through hull as soon as it is determined that the engine is not starting within the normal time.

2) Be sure the choke is closed completely. If an engine chronically starts hard, but then runs OK after it starts, the hard starting is almost assuredly caused by the choke not closing completely.

An engine requires three basic things to start: Fuel, Ignition, and Compression:

1) FUEL: Remove the flame arrestor and check for the presence of raw fuel. If the choke is closed completely, there should be raw fuel puddled in the bottom of the intake throat within 15 to 20 seconds of cranking (3 or 4 five-second attempts). If the carburetor intake throat is "bone dry", the reason for the non-starting is either a problem in the fuel supply that prevents the fuel from getting to the carburetor, or some problem within the carburetor that prevents the fuel from getting through the carburetor (most likely a blocked main jet).

2) IGNITION: Remove the secondary lead from the center of the distributor cap and hold it approximately 1/4" from the cylinder head while someone cranks the starter. You should see a good arc between the end of the coil lead and the head that can be stretched to 1/2" or even 3/4". If you see no spark, the reason for non-starting is clearly within the ignition system, most likely a breakdown within the primary ignition circuit. This check does not validate that timing is correct, so if the timing was altered during recent maintenance, it would be a good thing to reset the engine to number one TDC and recheck for proper timing.

3) COMPRESSION: With all spark plugs removed, hold your thumb over each spark plug hole sequentially to check compression, as someone cranks the engine for a second or two with the starter. An Atomic 4 will usually start if any two cylinders have normal compression as indicated below.

a. If you can't hold your thumb over the spark plug holes no matter how hard you press, the compression is generally normal (approximately 85 psi or above).

b. If you can hold your thumb against the compression, but not easily, a compression value of approximately 40 to 50 psi would be indicated, and starting could be problematic.

c. If you feel virtually no compression on any cylinder, the problem is likely a stuck valve.

Regards,

Don

[jkenan]

Thanks Don. The engine starts up just fine, and also starts immediately after a 'choppy water' shutdown. It pushes the boat along at 6 knots at 1800 rpm with a modest amount of throttle, so don't think compression or valves are the issue, and the engine seems to be getting all the fuel it needs (this is not a slow, gradual shutdown like what I've discussed with you in the past).

Would a fuel supply problem cause an immediate shutdown, or would it be more gradual? I've checked the needle valve, but not the main jet. Remember that the engine is able to start up just fine immediately afterwards and will run indefinitely if a get out of the chop.

My gut feeling says circuitry, unless you feel strongly otherwise.

Thanks for you feedback.

John

[Don Moyer]

John,

It would make things easier if the engine wouldn't start right back up after a shutdown, but you're probably correct regarding a loose connection somewhere in the primary circuit. If the fuel supply would break down during the choppy sea condition, you would think that the engine would be slow (or impossible) to restart until the choppy sea conditions abated.

Don

[tartan30cirrus]

John, Did you figure it out? I recently had a sudden shutdown in very choppy seas and the engine started afterward so I am curious.

BTW, I have experienced sudden fuel related shutdowns when the OP safety switch shutoff power to the fuel pump...I would think this would result in slow/soft shutdown as the remainging fuel in the carb got used up. But maybe the pump actually gets the fuel from carb to cylinders and would therefore cause sudden shutdown?

Let us know what you found!

Cheers,
Clint

[jkenan]

I was down on the boat this past weekend, and was not able to replicate the problem, since there was no wind and therefore no chop. Motored just fine...

I did tighten down all connections.

Another problem surfaced, however (which I'll post as another thread titled 'Coil energized with ignition switch off').

Will keep you posted on shutdowns and resolution, if any.

John

[Buck]

Intermittent shut downs in choppy seas might be caused by a hole in the gas tank pick up tube. Try changing gas tanks.