Flow rate from the fuel pump? Is air in the gas-line bad?

[liveaboardL]

What should the flow rate be coming out of the fuel pump:
A: When you short the safety switch
and
B: When you adjust the throttle while under way

For when the safety switch is shorted, I get a 15 second spurt of gas for every 30 seconds. The rest of the time it appears to be sucking air.
I just tried to purge the line and after running it for a good 20 minutes, long enough to make the (solenoid?) hot, it still does the same thing it's been doing for the last 20 minutes, sucking air half the time & spurting gas half the time. Is this normal? Will this cause problems when I put it into high throttle?

That's what I'm concerned about. It might be enough of a flow rate for low throttle, but not enough for high throttle. Does high throttle cause the pump to suck harder while at the same time allowing the engne to intake more fuel, vs: low throttle causing the pump to suck less fuel? Or is the fuel pump working at a constant pressure and the only dfference is the intake of the fuel into the engine?

Also, what happens with the excess air that's in the fuel line when it gets sucked into the carburetor? Does the carburetor have amechanism to deal with that, or will it cause the engine to perform badly?

If that air shouldn't be in there, how do I get it out? I lost 1/4 of a gallon purging the air I got out. If I left the switch shorted for 2 hours, would the air eventually all get purged out, or would he air pockes in the various twists in the hoses always be there contaminating the fuel. Someone mounted a tank-bypass switch and the water-remover filter so that it's not ontinuous slope down, but it's on a roller-coaster up & down & up & down again. Is this bad for the engine?

Thanks,
LL

[Al Schober]

LL,
Sounds to me like you're sucking air into your fuel line. The carb will eliminate the air through the float bowl, but the situation is likely to get worse rather than better (they always do). Eventually you'll be sucking enough air that there won't be enough fuel to run the engine.
Where's the leak? Well, what's between the fuel in the tank and the fuel pump? Could be anything from a pinhole in the pickup tube, a shutoff valve that's pulling air, a failed hose clamp, a chafed spot in the fuel hose, a crack in a copper line - the list goes on. Since you don't see it leaking fuel (have you checked?) it's probably above the level on the fuel in the tank.
Try filling the tank and looking for leaks. If the problem goes away, that in itself points to the pickup tube.
Let us know what you find.

[ndutton]

The others will be along after the holiday I'm sure.

I think there are two answers that cover most of the questions:

1. The electric fuel pump operates at a constant rate. It bleeds off flow internally when the carburetor float valve is closed. Greater throttle does not affect the pump. However, greater throttle does require more fuel than low throttle and the pump supplies whatever is necessary up to its maximum. By the way, the pump's maximum is over 30 times what the engine requires.
2. The carburetor float chamber is vented so any air that finds its way there is naturally aspirated. Air in the fuel line interrupts the flow to the carburetor and if enough air is present the fuel flow will reach a point of insufficiency for the engine to run. You need to find the source of the air leaks and resolve them.

A popular test is the auxiliary tank test. You set up an outboard tank with fresh fuel, hook its hose to the fuel pump inlet and test run the engine. A successful test clears the pump and carburetor. Then start adding components one at a time and testing again. You'll find it.

Two other comments.
Leaving the OPSS shorted and the ignition on for hours to purge the system risks death to the ignition coil. Please disconnect the coil before doing this or you'll be chasing another problem.

The fuel system does not need to be a continuous downhill slope. Solve these air leaks, confirm the pump performs to specification and confirm good, clean fuel and you should be well on your way to success. My previous suggestion on another thread of replacing the fuel lines throughout directly addresses the air leak problem by requiring you to revisit every connection. Canister filter seals are notorious for air leaks too.

[liveaboardL]

But isn't an air-leak in the fuel tank OK?

I suspect my fuel tank has a mystery leak in it somewhere. I saw some discolored fiberglass under the tank. The boat smelled hella awful after filling the tank for weeks & it gave me terrible headaches, but I initially suspected it was due to the gas-pump's either being 100% full throttle or completely closed while I was filling the tank. Gas sprayed all over the deck. I'm a trucker & I've used many nozzles, & have never dealt w/ that before.

Anyways, isn't a hole in the gas tank OK as long as the gas doesn't slosh around and drip from it? I have no idea where this tank breaths fresh air from but can't it just breath some from that hole? Seriously, I doubt this tank has an air-intake port. It's a big sealed iron tank w/ a gas-fillng screw and a discharge line, and a mystery hole.

What needs to be airtight is the tank's discharge line all the way to the carburetor, and if there was a leak, I'd be able to detect it.

Someone did recently install an auxillary tank switch, before I bought the boat. Now I know why. The PO went all the way to the Bahamas using the auxillary gas tank. I may have to buy a big jerry jug, syphon what's in the big tank and just use what I know works. I don't have money to make a lot of repairs.

[ndutton]

The situation as you've described with the main tank is dangerous, seriously so.

Further, I harbor safety concerns surrounding the discussion. A mystery hole in the tank, even if it does not drip fuel, can be a source of dangerous gasoline fumes inside the boat and presents the very real risk of catastrophic explosion. Your description of awful smells and gas spraying all over the deck while filling goes way beyond not good.

I try to avoid being an alarmist but in this case . . .
This is a dangerous and potentially deadly situation.

When I worked at the sailboat manufacturers we were always told that a single cup of gasoline spilled in the bilge once vaporized had the explosive potential of three sticks of dynamite. I don't think I can make this any more clear.

I appreciate budgets and all that but right now for the sake of your guests, slip neighbors and yourself the very best thing you can do in my opinion is get the gasoline out of the tank - all of it, make certain there is no gasoline spillage or fumes anywhere inside the boat (you'll have to get your nose all the way down in the bilge because gasoline fumes are heavier than air and therefore collect low) and then hire a marine surveyor to examine the engine systems carefully. His report will tell you what to do.

Please be safe.

[liveaboardL]

Great info

Very well said, and much needed information.

I finally found the air-intake tube.
I finally found where the fuel was stuck at.
I use the bilge-blower before starting the engine.
I checked the fuel tank after going for a short ride and it was dry underneath.
Plenty of people warned me about the LP, but I had no idea a gas-leak was that dangerous, but I'll be extremely cautious from now on, and recheck for leaks very carefully.
What I ended up doing was disconnecting the fuel lines in different places and blowing in them to see where the bottle-neck was at. The line going to the auxillary/fuel-tank/engine switch was the bottle-neck, so I just kept blowing into the hose while turning the knob around until the air easily went through.

One thing that prevented me from doing that earlier was that the hoses were so tight around some of the nipples that I couldn't pull the hose off them. I solved this by just cutting the hose off the nipple, sawing it w/ my knife, and then just reattaching it later. It didn't take that long either.

So, I've solved so many things recently and am so greatful for all your advice! Thanks. Who knows, it may have saved my life, for all it's worth. Cheers to you! & BTW I anchor out. & I have 4 fire extinguishers and I use the blower so, it's OK in this situation.

[ndutton]

What I want for you

Sorry for hollering and thank you for accepting it in the interest of safety. Of over 5,000 posts I've made on this forum (that alone is kind of embarrassing) I felt that one might have been the most important.

The difference between gasoline in cars and boats is cars do not have a sealed bottom where explosive vapors accumulate. Big difference.

What I want for you . . . .
is to become a marine fuel system expert. As time and funds allow make every component of the system first class and USCG compliant. I've attached a link to get things started . . . . and please do not assume the current installation is correct. It might be, I couldn't possibly know but it is imperative that you scrutinize it carefully as you proceed. We hear of one nightmare story after another courtesy of the PO's (Previous Owner's) handiwork.

Best of luck.

Title 33 CFR, Inboard Gasoline Engines

[Marian Claire]

"One thing that prevented me from doing that earlier was that the hoses were so tight around some of the nipples that I couldn't pull the hose off them. I solved this by just cutting the hose off the nipple, sawing it w/ my knife, and then just reattaching it later."
During my last "air in the fuel system" issue. I found two or three hose barbs that I had damaged/nicked by using a knife to cut the hose to facilitate removal. I replaced the damaged barbs.
Dan S/V Marian Claire

[romantic comedy]

Dan, you must have a heck of a knife to damage a barb!!
My houses never come off easy. Most times I cut them off. I never worry about a nick in a hose barb. Just leave a little extra hose.

[joe_db]

Did you ever find the leak?
I cannot say enough how this can KILL YOU

A leak in the top of the tank can be the worst because it isn't always obvious. Please let us know what you find. Keep in mind a gas tank has 3 connections - fill hose, vent hose, and fuel pickup. There should be ZERO fuel odor in the boat. To give you an idea of the force, look at the photo below. Crude oil contains gasoline along with all the other things you get from crude and oil tankers that do not take care with the fumes end up looking like this

[edwardc]

Dan, you must have a heck of a knife to damage a barb!!
My hoses never come off easy. Most times I cut them off. I never worry about a nick in a hose barb. Just leave a little extra hose.

I used to do that. Then I discovered the electric heat gun. Softens the hoses and they come right off with minimum trouble and no damage. Works particularly well on large stiff hoses, like those on seacocks.

[Marian Claire]

Dan, you must have a heck of a knife to damage a barb!!
My houses never come off easy. Most times I cut them off. I never worry about a nick in a hose barb. Just leave a little extra hose.

The damage I did was from cutting the hose parallel to the barb, splitting the hose. It leaves a small nick in the raised areas of the fitting.
Dan S/V Marian Claire

[Mo]

Just in...but pertinent

Today....May 29 2014 ... oil tanker explosion off Japan. Let's do it right and do it safe.

http://www3.nhk.or.jp/news/html/20140529/t10014813751000.html

[joe_db]

FYI - some tanker explosions in years gone by were caused by creative plumbing to try and run the engine from the cargo. The diesel engine systems were not set up to deal with a fuel containing gasoline and other light and explosive hydrocarbons. They also - as seems to be the case here - can be very dangerous when empty. Not sure why the tanks were not inerted

[JOHN COOKSON]

Not Intended To Pick on Liveaboard.......

But I want to correct a couple of misconceptions that I noticed.

I have 4 fire extinguishers and I use the blower so, it's OK in this situation.

Fire extinguishers are for fires. They're of no use in an explosion.
Blowers are meant to remove gasoline vapors. If there is liquid gasoline anywhere in the boat outside the fuel system it can still expolde blower or none.

Forget the tankers for a moment. Here's what it's like to have your boat explode.
I was walking down the marina about dusk one evening. I could hear someone grinding on the starter. Power boat - maybe 28 foot. The flash was blinding. The shock wave almost knocked me over. The heat was like a sun burn. The person doing the cranking was lucky. He (or she) was blown clear and landed in the water. Somebody around the marina said the boat had fuel problems*. There were a few spot fires on the boat. After they were extinguished the harbor patrol towed the boat out of the marina and beached it on the beach.

*Lesson here. If the engine doesn't start the way it should don't grind on the starter. It's not going to start anyway. Instead find the reason for the no start.

TRUE GRIT