Fuel-Related Engine Shutdowns

[Don Moyer]

From our Tech Tips section:

This tech tip is focused on the causes of fuel-related shutdowns, with a few suggestions for troubleshooting and remediation.

A good friend of ours from across the Chesapeake Bay had been experiencing regular engine shutdowns after motoring approximately 45 minutes to an hour, virtually every time he took his boat out. Finally, after much head-scratching, he discovered a pinhole in the canister of his primary fuel filter. It was not a RACOR filter, but it was of the same size and type as the RACOR filter and water separator shown in our online catalog. He replaced the fuel filter, and the shutdowns ceased.

The pin hole, though never manifesting as a fuel leak until my friend pressurized the filter, was apparently allowing enough air to be drawn into the fuel stream to form an air bubble which eventually reached the fuel pump and caused it to cavitate.

Around the same time that my friend had been sorting through his difficulties, Brenda and I acquired a small fishing boat to scoot around the tributary of the Chesapeake Bay that extends near our house. The boat has a small four-cylinder inboard gasoline engine, and incredibly enough, it was regularly shutting down every 20 minutes or so from what appeared to be fuel starvation, in much the same way that my friend's engine had been shutting off just a few weeks earlier.

I installed one of our new RACOR fuel filters soon after acquiring our little motor boat, and I had also installed a small rubber priming bulb between the tank (which is located lower than the engine on this boat) and the RACOR. The basic reason for the priming bulb is to prime the filter after replacing an element, without having to fill the canister with fuel and have it spill all over the engine compartment while I'm reinstalling the canister.

Much to my surprise, the first time I pressurized the RACOR and the rest of the fuel system with the priming bulb, two small pre-existing leaks showed up in fittings between the filter and the engine mounted mechanical fuel pump. The leaks were so small that I was never aware of their existence during normal operation, but they apparently allowed enough air to enter the fuel line under suction to shut down the engine for lack of fuel. The engine has never shut down since fixing the leaks.

I've been eagerly sharing these experiences with folks who have called in with fuel-related shutdowns over the past several weeks, and we've already had a few folks call back to report their own success stories in correcting small suction leaks in their fuel supply systems.

I'll try to consolidate and amplify a few key points:

1) Small leaks can apparently exist within a fuel supply system that will not manifest as fuel leaks, but which will allow enough air to be drawn into the lines to cavitate fuel pumps by the suction created during normal operation.

2) The high vapor pressure of gasoline exacerbates the problem of suction leaks by causing the air bubbles to enlarge somewhat after they form.

3) Electrical pumps seem to be somewhat more sensitive to the effects of air in lines than do mechanical pumps, although we have one recent case of fuel starvation caused by a leak above the sediment bowl in a mechanical pump.

4) Boats with tanks located lower than the top of the engine and at distances greater than 5 or 6 feet are more at risk of shutdowns from fuel starvation from small leaks in the system, due to the fact that more suction is created within their systems. Leaks in the fuel supply systems of boats with tanks higher and very close to the engine would probably manifest as fuel leaks and quickly be detected.

5) Air can be also be introduced into fuel supply systems while changing filter elements, and/or other maintenance, which will cavitate pumps, usually after a few minutes of running. Again, electric pumps are more at risk than mechanical pumps, since electric pumps make very poor air compressors. It's sometimes possible to prime filters after an element change by working the priming lever of a well maintained mechanical pump, but electric pumps will frequently never prime until the air is removed in some other manner.

6) Installation of a rubber priming bulb between the tank and the primary fuel filter will enable you to prime the system after replacing a filter element (or other maintenance), as well as to pressurize the system to check for leaks. The bulb also provides a nice diagnostic tool when troubleshooting fuel problems in general, by providing a second method of producing fuel pressure. In normal operation, the fuel pump is able to draw fuel through the priming bulb with little or no measurable head loss being added.

These priming bulbs (commonly used in outboard fuel supplies) are available from West Marine for 1/4", 5/16" and 3/8" fuel hose. At approximately $12, they may represent the best value you'll ever encounter in terms of enhancing engine reliability.

7) Many boats still have small screens over the ends of their pickup tubes which become clogged quite easily, and are really unnecessary after the installation of a proper primary fuel/water separating type of primary filter.

8) Lastly, spring-loaded check valves used as anti-siphon devices sometimes cause or at least exacerbate problems. These valves are usually installed where the pickup tube leaves the top of the tank and function by adding more head loss (approximately 2 psi) than the weight of the fuel in the line downstream of the tank. In this way, if you leave your manual shut-off valve open while leaving the boat unattended and a major leak develops, fuel will not flow from the tank. These valves are OK in principle, but the "controlled restriction" that they introduce, does have the potential of creating problems in some fuel systems. For example, I think they would be really troublesome in the Catalina 30 fleet, with fuel tanks so low and far from the engine.

Hopefully, these suggestions might help to identify a few latent problems that may be lurking in other fuel systems before the onset of frustrating shutdowns related to fuel supply problems.

Don

[autorot8]

It worked!

Don,
I read this article over and over...it made alot of sense. I took all of your suggestions and put them into play.

From you I ordered, then installed a new electric fuel pump, water filter/seperator. I installed new 5/16" fuel lines from tank to carb and a prime bulb that is easily accessed in cockpit.
The installation took about an hour, the prime bulb primed and pressurized system in a few squeezes.
The engine fired right up and runs a heck of alot better. I motored around for over an hour and it seems that the engine is almost as good as new. Temp never went over 140, oil pressure was great and she seemed to purr like she hasn't in a long, long time.

The overall first impression is that the mechanical pump was not providing sufficient supply of fuel and that it leaked air via the glass sediment bowl. The electric fuel pump seems to provide more than adaquate fuel supply. The engine runs smoother and is more responsive. Wish I had made these improvements sooner...
ALL Atomic 4 engines should have these upgrades in my opinion. It has made a huge difference to my boat and my love/hate relationship with these engines. I even considered retiring my atomic 4 and going to a long shaft outboard until I could afford a repower to diesel... Well now, I seem to be satisfied with the results of these products.
I had never heard of fuel related engine shutdown, now I wont have to experience it anymore either.

[laserandy]

Any modifications to use electronic pump?

Did you have to remove the mechanical pump, or did you just put the electronic pump inline and have at it?

Andrew

[autorot8]

mechanical pump

I basically replaced the entire fuel system and effectively retired the old mechanical pump.
The old pump is still attached to the engine block. I did remove ALL the fuel lines from old pump and also removed the sediment bowl. The old pump is now just an eyesore.

I placed a towel on top of pump, so that when engine first fired up with new parts, the residual fuel (left in pump) would not be sprayed all over the engine. Good thing to, the towel was saturated!

[Administrator]

If you decide you want to remove the old pump, here's the cover plate you'll need.

Bill

[cc29_buckeye]

Fuel Frustrations...

As we were returning from a week long cruise, my engine (1977) started showing signs of fuel starvation (and of course a loss of power). Although it never died, it ran extremely rough only while under load (e.g. only in gear). I did have to be towed in the last hour of the trip.

I replace the in-line fuel filter prior to the trip and motored for more than 15-20 hours prior to this problem. I did notice (it is a clear filter) it runs seemly dry during most operation. I did not "bleed" the system after replacing the filter because I was told with gas engines, the fuel pump will pull what it needs (I have an electronic fuel pump).

I have been reading a bunch and am thinking it may be a blockage but before I pull the pick up tube and possibly the tank to inspect and clean it, I would like some suggestions...

I intend on replacing the fuel lines (incase I have an air leak) and adding a priming bulb to prime the system and see if this corrects the problem. Any other thoughts???

Thanks!

[Don Moyer]

I believe you're on the right track. One additional consideration is that electric fuel pumps do not create suction head nearly as efficiently as mechanical pumps, so they are not quite as forgiving of small amounts of air in the system.

Don

[J. Fred Bear]

Primer bulb location?

I want to install a primer bulb. Where, exactly , does it go: between fuel
tank and fuel filter?; or fuel filter and engine; or some other place?.

Can you connect it with regular small hose clamps?

Also, I'm ordering a Racor. You suggest an inline filter as well. Where does
this second filter go?

Thanks.....



Fred Bear

[Don Moyer]

Fred,

The priming bulb mounts between the fuel tank and the RACOR filter.

The inline (secondary or polishing) installs between the fuel pump and carburetor.

Don

[J. Fred Bear]

Primer bulb ok!

Don

In installed a primer bulb between the old gas filter (Fram.....made in Turkey...the country....not the thanksgiving bird.)
and the gas shutoff cock.

Works fine......filled the entire gas line to the carb very fast......

Thanks for the suggestion.

Engine still would start...run for a few seconds...then quit.....
So I removed carb....left it with a small engine mechanic....he will check for
obstructions in the jets......I
I found small bits of soft black material in the gas....mechanic says its residue from old rubber gas hoses and that CAN clog the jets.
So I'll replace the hoses too.

So the situation goes on..........sooner or later I will get this atomic beast to
run....

Fred Bear

[Angus]

For quite some time I have experienced an unexplained engine shutdown. Sometimes even after running a hour and sometimes after only less than a minute after startup. I have gone through the recommended procedures to detect the fault, finally arriving at the conclusion fuel starvation is my problem. I have dismantled and thoroughly cleaned the Zenith 61 carburetter, and having installed a kit only two years previously did not, at this time, think about replacing any parts of the carburetter after checking the integrity of the float, its setting in relationship to the casting etc. Finally I deduced the float valve may not be allowing fuel to flow into the chamber. On the next occasion the engine stopped (alongside the dock) I carefully removed the carburetter holding it in a level position I removed the four screws and lowered the bottom casting to expose the float and noted the pin valve had not dropped down as it should have when the floats dropped thus shutting off the fuel supply to the bowl. I disassembled the float and the valve seat to check for some obstruction and there was none. I used fine steel wool to make sure there was not gum on the triangular sides of the valve and the valve seat. After re-assembly I noted that the pin still remained seated after being pushed up against the seat (see attachment). I carried out this procedure perhaps three times and finally ordered a new valve and seat from Moyers. This I installed and within three weeks I experienced the same symptoms. When I talked to the representative at Moyers, I asked about ethanol deterioration of the plastic/rubber 'tit' on the end of the triangular valve, due to ethanol additives. There had been no reports. I think there might be a correlation here. A fellow Atomic4 owner noting my frustration, suggested I use his old spare Carburetter. After fitting it the engine ran for an hour without hesitation! The control hookups were different and would need alteration so I decided to dismantle the replacement carburetter and only use the valve and seat. It was at this point I noted a difference, taking the valve out of its seating I noted the point was steel, not rubber/plastic. I fitted the assembly to my engine and it has run without faltering ever since. Now I am hoping I can obtain an all steel valve for my carburetter.

Cheers, Angus

[lhbradley]

Priming bulb caution

Don recommends an outboard-style priming bulb. I put one in my fuel system about 4 years ago, because the priming lever on the mechanical fuel pump was partially broken and didn't work too well. The bulb worked well.

Last year I changed to an electric fuel pump, and left the primer bulb in place. On a few occasions during the year, the engine would just quit. Squeezing the priming bulb allowed me to start the engine and all would be well for several weeks. It was suggested to me that there might be an air leak, but I could not find anything.

This year, one day the engine would not start. At all. Squeezing bulb didn't help - in fact, bulb was very had to squeeze. I removed the bulb from the fuel line, and the problem disappeared. I took the bulb apart, and found that one of the balls in the valves was sticking, not allowing fuel through.

Moral of the story:

If you have a fuel starvation problem, bypass the priming bulb as one of your tests.

And perhaps taking the bulb out once a season and cleaning the valves might be a good idea. They use spring-type clips on the bulb, but after taking it apart, you could use hose clamps, since the clips probably won't go back on properly.

Or just replace the bulb every year or two.

[baileyem]

a different twist

My A4, early model, with mechanical fuel pump & std ignition system, has just developed what seems to be a fuel related problem similar to those described above, but with a different twist....the engine starts and runs well, When I push it to 1700 rpm it runs well for 3 to 15 minutes at that speed and then begins to rapidly lose power and rpm to about 800-1000. ( it sounds like it is starving for fuel, but doesn't cut out completely ) If I don't mess with the throttle setting the rpm will slowly crawl back up to 1200 where it will run very nicely for an unpredictable amount of time before running through the cycle again. However, if when the power first drops, I cut back the throttle to 800 rpm and then advance it to 1500 rpm, the engine will run at that setting very happily until I choose to change the throttle setting. For some reason the engine does not like to run at 1700 nor can I get it to reach anything above that.

I suspect that my float level is not set high enough, or my fuel pump will not deliver the amount of fuel required at the higher throttle settings.

I would appreciate any comments on my problem before I tear into it.

Thanks, Mike

[jhwelch]

I bet your carb. float is sticking and not opening fully. I've temporarily
fixed this by tapping on the carb. Sometimes it lets the float drop free.
Once I get to a stopping point I take the carb. off and clean it out.

-jonathan

[Don Moyer]

Mike,

I agree with Jonathan and would add that your symptoms are also consistent with low fuel pressure. I'm attaching a troubleshooting guide to check your fuel pump.

Don