Fuel-Related Engine Shutdowns

[baileyem]

Thanks

Thanks Jonathan and Don for the quick responses.

Mike

[baileyem]

follow-up on problem

Just a quick follow-up on my fuel problem.....Jonathon and Don were right, I ran Don's suggested test on my fuel pump and it seems to be OK. There was a lot of crud in the carburetor that I flushed out by working the mechanical fuel pumps priming arm after I had removed the main carb drain plug. So the problem was definitely dirt in the fuel that may have been giving me carb float problems as well as possibly dirty jet problems.
I did clean and change my filters before taking her out for an extended run. I am happy to say that the engine never hesitated, ran well under load, and produced 1800 RPM without problems.

The problem is that now I have to haul for the season next weekend.

[rpn59]

Fuel starvation

Hi Don,

I read a bunch of articles on the the forum where people have considered fuel starvation as a possible problem for their ill running engines. A good and very simple technique is to spray a little starter fluid into the carb and see what happens, if the revs pick up or the engine continues to run then you know the engine wants more fuel than your fuel system is delivering and hense you need to look at the entire system to find the fault. If not, start looking at other systems, no?

Ray

[Bob.Griffin]

This thread has generated much interest, and here's my convoluted addition, which to me is a bit of a puzzler. I have a fairly new s/s fuel tank installed by the PO but it has no opening for the fuel guage sending unit, just a small 5/8 inch opening with a bolt that the PO used with a dipstick to check fuel levels. Being a perfectionist, I wanted to have the fuel guage work properly. I wasn't prepared to remove the tank (meant dismantling half the rear end of my boat!) and have a new port cut into it, so I decided to install a small secondary tank with a syphon connection and containing a new sending unit. The syphon is a copper tube going to the bottom of the primary tank and a clear poly gas line to the secondary tank which is also vented (I wanted to use clear poly initially to check it all works). It all works fine but I noticed that tiny air bubbles could be seen coming from the primary tank and very slowly filling the syphon line with air over a period of 4 or 5 days, such that the syphon no longer works. I've checked for leaks and found none, so assumed this was dissolved air in the gas coming free (I'm no hydraulics expert!). I use a bulb to prime the syphon every time I use the boat. My question is: if this air is evolving in my syphon line, it must also be slowly filling the main line to the fuel filter as well and I wonder if sometimes the electric fuel pump cavitates until the air is eventually sucked through (main tank is above the engine and only about 2 to 3 feet from the carb), because sometimes the engine starts very rough when started and runs rough for about 10 minutes then runs fine. Am I way off course or is this possible?

Bob Griffin
C&C Corvette 'Saga'
Bath, Ontario.

[Don Moyer]

Bob,

You pose a very important question in my view and I hope others will contribute.

I'm not a hydraulics expert either, but we do know that the vapor pressure of gasoline is quite high which means that it doesn't take much of a pressure reduction from normal atmospheric pressure before evolved gas will start to come out of solution and create bubbles. When the reduced pressure equilibrates, I believe the evolved gas goes back into solution, but I'm not sure if it passes back and forth from solution at the same pressure; i.e., it may take positive pressure above normal atmospheric before the evolved gas will go back into solution.

I believe it is also true that the vapor pressure of gasoline becomes higher as temperature rises, which means that if you do have any restrictions in the fuel supply line from the tank, the tendency for gas to evolve out of solution would be worse in the heat of summer. This is probably what oldtimers used to call shutdowns from "vapor locks".

Don

[baileyem]

vapor lock

Don
I don't think of myself as an 'old timer', but yes we used to experience vapor lock in the 'old days' (hey, I'm only 67). I drove a lot of Ford flatheads that would have problems in hot weather if the fuel lines and fuel pump got to hot. The cure was to either cool the fuel lines and pump with damp rags and cold water or to crack a fitting on the high end of the fuel line and release the air bubble. I never heard an explanation of what caused the problem. I just learned how to recognise it and how to deal with it. I think that we figured the gas got hot enough to boil, and that the boiling caused the bubble......from your explanation, I guess that is a reasonably close explanation.
I can see where an A4 stuffed into a hot, poorly ventilated engine compartment could easily develop 'vapor lock'.

Mike

[Bob.Griffin]

Don/Baileyem:

Very interesting, this also explains why plastic gas cans tend to expand in hot weather. Can someone take this a step further and expalin what are the typical symptoms of a 'vapor lock'? Can one get a partial 'vapor lock'?

Bob

[Phil]

http://en.wikipedia.org/wiki/Vapour_lock

[Don Moyer]

Good article, Phil!

Don

[Bob.Griffin]

Thanks Phil, that certainly helps. I imagine the problem with boats is when they are left for periods of time (during the week when we have to work) and in hot weather, the vapour lock slowly forms over time. I'm temped to test this theory by replacing the gas line from tank to fuel pump with a clear plastic line and see what happens. My gas line comes out of the top of the fuel tank which doesn't help, if it came out of the bottom of the tank and runs down hill to the pump, I'd never get a vapour lock. What happens to the vapour lock when it hits the fuel filter?

Don, rather than replumbing my fuel tank (highly unlikely), will a prime bulb fix the problem? I do get stalling and poor running for about 10 minutes after I start from cold, and the choke helps a lot which does suggest fuel starvation which I think is caused by a vapour lock.

Bob c/o Saga, Ontario

[Don Moyer]

Bob,

In spite of my enthusiasm for priming bulbs, having installed one on my own boat, I wouldn't promote them on the basis of having a positive effect on vapor locks (as we're beginning to understand vapor locks in this thread), since they theoretically add a bit of head loss in the supply line. I would continue to look for any cause of elevated head loss in the system from the pick-up tube in the tank to the inlet of the pump. One of our customers recently cured his fuel supply problem by replacing 1/4" fuel line from the tank with 3/8" fuel line.

Don

[Jesse Delanoy]

Bob,

Don't re-plumb your fuel tank. Gas tanks always draw fuel out from the top of the tank. That way, if you have a tank fitting that develops a leak, your tank won't proceed to quietly empty itself of gasoline into your bilge (not a good thing!).

[Rich Chandonnait]

new carb

I have recently bought a new carb (Zenith) and it came without the needle valve on the bottom of it,I was told that it did need it is this correct,Don do I need the adjustable needle valve or is it set from the factory it came from Moyer marine

[Don Moyer]

Rich,

All new late model Zenith carburetors come from the factory with fixed main
jets. You do not need to install anything additional prior to installing
and using your new carburetor.

Don

[burnell]

Another fuel related shut-down

Don,

This is my second exposure to the A-4. My first was in a Cheoy Lee named We're Here, which I sailed to AYC for your one-day lecture on the A-4.
I have just became co-owner on a wooden-hulled H-28, circa 1962. Bringing her home to Annapolis from Oxford last week, the A-4 engine died after about 45 minutes.

Luckily, a freshening breeze gave me lots of time, so I removed the ancient Racor. It's mounted at the highest point possible, above the fuel tank in the sail locker, and the electric pump is near the engine after about 4 feet of copper tubing. There was about 10% water in the bowl, with lots of brown flakey stuff that seemed to increase in volume with exposure to air and sunlight.

I blew into the tube to dislodge any obstruction in case there was a screen at the intake inside the tank, shook and toweled the old cartridge, and, having no replacement, I put it back. The engine restarted, but we used it only for bridge and docking maneuvers.

The next day I was amazed that West Marine had a replacement for the antique cartridge. They did not have replacement 'O' rings for the Racor fittings, so I bought approximate sized replacements at a hardware store. The next day was a repeat of the first in that the engine died after 45 minutes. This time there was no water or debris at first, although some of the brown flakes showed up after exposure to sunshine.

I will immediately add the squeeze bulb you recommend in this thread, and look for leaks. Should I also replace the 'O' rings with parts designed for gasoline? The gas smells stale to me, but mechanics have said it's not so stale that it should affect operation, and certainly not after 45 minutes of operation. Does it sound like I should try to clean the tank? The mechanic said not to discount other possible causes. Is this a good time to replace the ancient coil or to go to electronic ignition? Any other thoughts for me?

Burnell

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