Engine shuts off

[dwoodriff]

My Atomic 4 shuts off after about 3 - 4 minutes, consistently. (that's nice anyway, at least it is consistent) I have had the tank steam-cleaned and painted inside, put a squeeze bulb, then Racor filter, then electric fuel pump and last a finishing filter just before the carburetor. It starts up nicely after priming with the squeeze bulb.

Then it runs fine for 3 - 4 minutes and shuts off. If I immediately re-prime the system with the squeeze bulb, it starts up right away again and runs another 3-4 minutes.

If I prime the system and then close the valve leaving the fuel tank, it starts right up and runs about a minute then shuts off, which makes sense as fuel can't leave the tank. At this point, the squeeze bulb is completely deflated, with no "squeeze" left in it, sucked dry by the fuel pump. If I re-open the valve leaving the tank, re-prime it with the (now expanded) squeeze bulb it starts right up and runs fine for about 3-4 minutes again, then shuts off.

Any suggestions would be appreciated!

[Dave Neptune]

d/w, you will need to isolate your fuel delivery problem. First are you using the stock mechanicle fuel pump or an after-market electric. Second, is your priming bulb colapsing when you do not have the fuel valve shut off? If so the problem is in between the bulb and tank, if not it is between the bulb and the carburator as you have not indicated any problem with the engine running just dying!!! I assume you have a mechanical pump which has a setiment type filter on the intake side of the fuel pump--CHECK TO BE SURE THE SCREEN/FILTER IS CLEAN and THAT THE GASKET SEALING THE BOWL IS IN GOOD SHAPE! If the screen is plugged NO fuel flow and if the gasket leaks no suction=no fuel flow. A good idea is to mount a F/pressuer guage between the F/pump and the carb because if you have fuel pressure at the carb then something in the carb (in this case the carb does not appear to be the problem only getting it fuel) could be the culprit. On my boat I have a F/pressure guage mounted in the engine box so I can see it when the cover is open--all I have to do is look and I KNOW the fuel system if functioning properly as far as delivering fuel to the carb is concerned.

Hope this helps---Dave Neptune

[Dave Neptune]

dw, forgot one thing if you have the mechanicle F/pump there is a bail hanging around the pump that is for priming the system after it has been shut down for a long time. If you work the bail by hand and you can keep the engine running it is probably something in the pump itself. One step at a time as it is usually somethinmg basic that causes problems. Also check and replace any inline filters as well.

Dave Neptune

[dwoodriff]

Thanks for the reply, Dave. I have an electric fuel pump installed (Moyer Product No. - FPMP_01_44) and the manual fuel pump removed. Also installed is an in-line finishing filter between the electric fuel pump and the carburetor. The electric fuel pump is mounted below the level of or lower than the carburetor and the fuel filter and fuel tank and seems to pump quite well. The top of the Racor fuel filter is level with the top of the tank where the fuel feed tube comes out.

The primer bulb is not collapsing when the engine quits with the fuel valve open, it only collapses when the shutofff valve is closed. I can eaisly and quickly "pump" it to prime the filter and fuel pump and re-start the engine immediately.

The engine runs fine when it is running, even under power, but only runs for a few minutes.

[HOTFLASH]

Check that the vent is not clogged. Spiders, etc. If so, that could stop the gas flow and cause what you described. Good luck!
Mary

[dwoodriff]

Thanks for that. I don't think it is the vent as I removed the tank fill plug and ran the engine with it removed and is still cut off after 3 - 4 minutes.

[Dave Neptune]

dw, are you sure the pump is still running while the engine is? Could be a problem with the oil pressure cut out switch.
You could get the engine primed then remove the Fuel line and place it in a suitable container to catch the fuel, start the engine and see if the pump continues delivering the fuel while running.

Dave Neptune

[dwoodriff]

That is a good idea, Dave! I have an oil pressure safety switch (FPMP_04_46) installed. The pressure gauge usually reads 45-50 lbs after the engine starts up and is running; but perhaps somehow the safety switch is turning off the engine (and the electric fuel pump).

I will try shorting or bypassing the switch to see if it continues to run or shuts off after about three minutes.

[jhwelch]

When I switched over to an electric fuel pump and an oil pressure
safety switch I had some electrical issues that were blowing the
fuse to the pump, so I used an old switch that had been retired from
some other job as a bypass, so I could turn it and have the pump
always on, in case of the fuse blowing in a bad spot. That's also helpful
to have when priming the system after having the carb. off. (And yes,
I have since fixed that pesky electrical problem, it was a failing connecting
causing current to flow through other wires).

-jonathan

[dwoodriff]

I by-passed the oil safety switch, and this made no difference. The engine still shuts off after a couple of minutes.

I removed the Racor fuel filter from the fuel line, made no difference. Then removed the pickup tube and shut-off valve from the tank and ran a tube directly from the fuel in the tank instead, no difference.

I put some gas in a water bottle and ran the fuel line into that through a hole in the top, turned it upside down and held it above the engine, in the cockpit and the engine runs fine and does not shut off. The fuel line goes to the electric fuel pump, then the final in-line filter then to the carburetor.

Perhaps a hose clamp is not tight enough or the hose is collapsing. Each time it shuts off, I can pump the priming bulb a couple of times and the engine starts right up.
?

[Dave Neptune]

D W, if you can feed fuel from a bottle held above the engine and it runs, could be a couple of things. One the added F/pressure from the fuel being held above is just enough to keep it going could indicate a weak pump or plugged inline filter. OR----you have an air leak in the system behind the F/pump, allowing it to draw air (fuel is about 600 times less dense and that much easier to draw onto the line) greatly reducing what is not much pressure when it is working properly. This can be a bigger problem if the tank is below the engine.
You can eliminate a lot of diagnostic issues by just installing a F/pressure gage between the carb and the mext thing upstream be-it filter or pump.
You have estabblished the engine runs with your bottle trick, I suspect the primer bulb could have a minor leak as it has four clamps on it. I have had many an air leak screw up my big and little outboards and most of the time it was a matter of replacing the squeeze bulb or replacing the factory clamps with screw type or the O-ring at the quick disconnect.

Dave Neptune

[rigspelt]

Don has a nice anecdote here http://www.moyermarine.com/shutdowns.htm about chasing an engine shutoff problem on a boat that turned out to be a fuel line leak. After pressurizing with the hand bulb, search the fuel line carefully for a fuel leak that could work in reverse to suck air when the engine is running. But smaller air leaks are possible too. Inspect all the fuel line connections. Look for things like a hose clamp crimping a hose that is a hair too big for a hose barb, that kind of thing.

[dwoodriff]

I have run the engine with only the fuel line, no primer bulb, no pickup, no Racor filter; only the electric fuel pump (brand new) and, before that, the manual fuel pump, with same results, shuts off in two minutes.

I previously (last week) replaced the manual pump as I felt that this might be the problem, but problem persists.

When the bulb is inline and I squeeze hard there is resistence but no leak visible.

I am going to replace all of the fuel line and clamps (which are all new, but two brands) with new line and clamps and tighten all very well to see if this gets rid of the problem. I think (at this point) that it must be a very small air leak letting in air somewhere between the tank and the fuel pump where there is suction. If it were past the pump toward the carburetor, it seems that gas would leak out rather than air leaking in.

[rigspelt]

No I'm really curious. Summary:

Problem: Engine shuts down at 3-4 minutes of running. Priming with squeeze bulb allows a restart, then same problem recurs.

The problem is so consistent at 3-4 minutes: surely that points to only a few possiblities? Clearly, there is enough fuel to supply the engine for 3-4 minutes. This suggests that a restriction starts building up that takes 3-4 minutes to become complete. Does not sound electrical, so seems to my amateur mind that it must be fuel starvation.

No difference after:
Tank cleaned/repainted.
Added Racor primary filter.
Replaced manual fuel pump with electric.
Added a secondary fuel filter.
No difference if vent bypassed.
No difference if oil pressure safety switch bypassed.
No difference if Racor filter bypassed.
No difference if fuel tank pickup tube and shutoff valve bypassed.
No difference if only the fuel line is used.
No gas leak in the distribution system when pressurized by the hand bulb.
Problem gone if supply engine with gas from an open bottle through a different fuel line to the electric pump, held above the engine in the cockpit. This means that the problem must be somewhere in the intact fuel distribution system before the electric fuel pump.

1. Vapor lock? Something must have changed to make that start happening. Tiny air leak in the fuel line still possible, I guess.
2. Nobody has mentioned the carb yet, but seems to me I've read some posts where a pesky and easily fixed carb problem can cause fuel shutoffs. I now the engine runs fine from a bottle in front of the carb, but maybe the physics of the carb have changed so that the pump cannot force gas through some restriction in the carb, or a defect in the carb builds up pressure that the pump cannot overcome?
3. Is there an antisiphon device in the fuel line?
4. Hidden restriction in the fuel line? Previous posters have talked about delaminating fuel line, or a defective hand bulb.

I'll be interested in hearing the result of changing the fuel line.

Another item worth reading: http://www.moyermarine.com/faq/11.15.html

[dwoodriff]

Yes, "rig" I am thinking along the same lines you are. Thanks for your interest and for the very clear summary of my "progress."

I shall replace all of the fuel line today with new, tighten all clamps really well and try it. If the problem persists, I plan to remove the carburetor and rebuild it.

(Also, I'll have a look at the points, just in case. Another thing entirely, when I look at the engine closely at night, I can see some spark leaking by the plugs and entering the block next to the base of the plugs. Is this common, or should I replace the spark plug wires?)

[msauntry]

Time for new wires when you start seeing the strobe light show in the engine room.

[dwoodriff]

Thanks for that, I will get the wires and tune it up also.

I called Don and he suggested that I look at the problem from the other end, starting at the carburetor. The simplest of things, it turned out to be. Apparantly the original problem was the mechanical fuel pump, as I installed a new electric pump and neglected to ground it, and the engine kept acting the same. When I grounded the new electric fuel pump (it is mounted on a bulkhead), it fixed the problem completey!

Thank you all for so much help. I feel really stupid about this, as I should!

[rigspelt]

Doh. But, interesting to know that squeezing the bulb filled the carb with enough fuel to run the engine for 3-4 minutes, and then it shut down for lack of fuel because the electric fuel pump was not running. That's useful information for me from your frustration. Glad you found the problem.

[Baltimore Sailor]

Heh. It's too bad no one thought to tell you to jump the electric fuel pump straight from the battery to see if you could hear the telltale tick-tick-tick of the pump running. You'd never hear it over the engine, but it's clear enough if nothing else is going. I didn't even think of it until you said you'd found the problem.

But at least you found the problem. That's a winner!

[jhwelch]

I have a switch I can throw that turns my fuel pump on. Useful in case
its fuse blows in a place where I really need to have the motor running
or after changing out the big fuel filter, so I can draw fresh fuel from
the tank into it.

-jonathan

[Harris Huberman]

I had a similar 'shuts off within a couple of minutes' problem with my A4 - recently rebuilt by Don's shop. Pat McGovern - a City Island friend who'd had similar problem, suggested the electric fuel pump shut-off switch could be the cause, and in fact when I bypassed it with an alligator clip setup from a hot wire on the coil directly to the fuel pump, the engine ran fine.

I've enjoyed the rest of the season with the Atomic running like a charm (except for when the alligator clip falls off), but would like to do a definitive fix (and restore the shut-off safety feature).

I'd appreciate suggestions on how to proceed. I first thought to replace the oil pressure sensor, but the oil pressure guage goes from 0 to about 40psi when I start the engine, so I figure the sensor must be okay. Is there a replacement wire harness I can just switch? It may be apparent that the boat's wiring is my least favorite area ... and I'm avoiding actually getting out the ohmeter and checking the connections themselves.

Suggestions...?

BTW - how the heck do you post to start a new thread?

Thanks, Harris

[rigspelt]

Originally Posted by Harris Huberman

I had a similar 'shuts off within a couple of minutes' problem with my A4 - recently rebuilt by Don's shop. Pat McGovern - a City Island friend who'd had similar problem, suggested the electric fuel pump shut-off switch could be the cause, and in fact when I bypassed it with an alligator clip setup from a hot wire on the coil directly to the fuel pump, the engine ran fine. I've enjoyed the rest of the season with the Atomic running like a charm (except for when the alligator clip falls off), but would like to do a definitive fix (and restore the shut-off safety feature). I'd appreciate suggestions on how to proceed. I first thought to replace the oil pressure sensor, but the oil pressure guage goes from 0 to about 40psi when I start the engine, so I figure the sensor must be okay. Is there a replacement wire harness I can just switch? It may be apparent that the boat's wiring is my least favorite area ... and I'm avoiding actually getting out the ohmeter and checking the connections themselves.

A word of caution, I am not a mechanic. There are other possibilities than these:

It sounds like you may be bypassing the oil pressure safety switch and its wiring. If that is true, then perhaps the oil pressure safety switch is defective, or the wiring from coil to switch to fuel pump is defective, or the switch is not properly grounded. The switch I got from MMI does not allow electricity to flow until (unless) there is a bit of oil pressure.

There are three oil pressure ports on the port side of the engine block: one forward just behind the flywheel, one middle under the carb and therefore useless in many cases, and one aft near the fuel pump. The oil presssure gauge normally is supplied by a sender wire from an oil pressure sender attached to the engine block at the forward port. The oil pressure safety switch is normally installed in the aft port near the electric fuel pump. It is possible to have a third oil pressure sensor too: one that triggers a buzzer alarm if the oil pressure drops too low. You may or may not have this third sensor. It is usually is mounted at the forward port on a T along with the oil pressure gauge's sender. (I cannot get the plug out of the 3rd, aft port near the fuel pump, so I have to mount all three oil pressure sensors in a cluster on a bulkhead-mounted hose off the forward oil pressure port: the oil pressure gauge sender, the oil pressure alarm buzzer switch, and the oil pressure safety switch for the fuel pump.)

Trace the wire from the coil (+) post to the fuel pump. Is there an oil pressure safety switch in that pathway? If MMI's shop installed it, then it is probably in the 3rd (aft) oil pressure port in the engine block, just aft of the fuel pump (if the fuel pump is attached to the engine and not a bulkhead off the engine). It should be screwed directly into the aft oil pressure port near the fuel pump, or attached by a small brass pipe screwed into that port. They can also be installed on a nearby bulkhead, attached to that port by a sturdy hose.

Once you find it, check all the wiring from coil to fuel pump to make sure it is in good condition and not chafed, that the connections are clean and tight, and that the oil pressure safety switch is grounded. There are two ways it can ground: (1) if it is screwed into the engine block, or into a metal nipple screwed into the block, or (2) if it is attached to a bulkhead, in which case it needs a ground wire attached to the block or a ground bus.

If the wiring is OK, then perhaps the switch itself is defective.

If all this is not the case, then I am taking you down a wrong path.

Does that help? Having stuck my neck out with this, I would not be surprised if someone else replied with a much more authoritative, useful and correct answer, so take this with a grain of salt.

Originally Posted by Harris Huberman

BTW - how the heck do you post to start a new thread?

Open one of the discussion topics halfway down the page at http://www.moyermarine.com/forums/index.php and click on "New Thread". Like most forums, you may have be registered to post, and I presume this one is the same.

[Administrator]

BTW - how the heck do you post to start a new thread?

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Starting on the forum's index page, left-click on the Discussion Topic where you'd like to post your message. The various topics are listed under a heading by that name, and include such things as General Interest, Troubleshooting, General Maintenance, etc. You may have to scroll down the page a ways to see them.

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Bill

[Don Moyer]

Harris,

I recommend you check the inline fuse between the coil and the oil pressure safety switch before doing anything else. Your jumper wire appears to come directly from the coil which would bypass that fuse. These fuses will sometimes get shorted out and blow during the time of an engine installation.

The fact that your oil pressure gauge works OK has nothing to do with the functioning of the electric fuel pump circuit. The oil pressure safety switch is a separate normally open pressure switch that only controls the flow of power from the positive terminal of the coil to the pump.

Don

[Harris Huberman]

Thanks, Don and Rigspelt -

Will check the connections from the coil to the oil pressure safety switch (including the fuse) - if these all seem to be okay, will replace the oil pressure safety switch.

Harris