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]

Fuel starvation?

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]

Fuel starvation pt II

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]

Engine shuts off

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]

Is vent clear?

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]

Engine shuts off

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]

Fuel starvation

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]

Engine shuts off

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]

Fuel Starvation

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?)