fuel starvation - pickup tube or other problem?

[capnrobalo]

Hi,
I have a problem with my motor getting fuel under the following conditions:

1) when the fuel level is low (after a day of offshore fishing)
2) when the seas are rough

Basically, what it boils down to is that on my way back in from offshore, sometimes when the boat pounds the water after going over a big wave, the motor rpms suddenly drop without me touching the throttle. Usually, the motor continues to run but at low rpms. Sometimes but not usually the motor cuts out entirely. When either of these symptoms occurs, I have noticed that there is air in the priming bulb. And if someone constantly pumps the bulb, I can keep the motor running just fine at 4000-5000 rpms. Of course this is quite annoying and scary and I would like to get it resolved before going offshore again.

My mechanic has attempted to fix this problem in 3 or 4 different places but without success. Now I am now trying to take care of it myself. I believe the problem is a poor design on the fuel tank/withdrawal system but I'm not a boat builder and don't have much experience with marine fuel systems.

The fuel tank is a 99 gallon aluminum below deck tank. I don't have access to remove the tank, but today managed to remove the pickup tube. Attached are a couple of pictures of it. To me, the pickup tube looks suspect. It seems to be bent upwards near the end of it which seems to me like a problem when fuel is sloshing around in the tank. I suppose that this is something that occurred over time and was not part of the original design. Also, why is there a plastic fitting on the end? It looks like it possibly connected to another tube or filter or something. Also, does it seem kind of long for a pickup tube or is this normal? I am under the impression that a pickup tube normally sticks straight down and off the bottom of the tank a quarter inch or so.

Anyway, can someone offer some hints or suggestions as to how I can resolve this issue? It is frustrating always having to limp back in from a day of fishing. And if any more information is needed to help diagnose the problem let me know. Thanks for any help!

Jason
1996 Robalo 2120

 

[dingbat]

Re: fuel starvation - pickup tube or other problem?

I had the same problem on the Grady last year. The rpm didn't drop out but I was getting alarms under the same circumstances. I pulled the back flow preventer to no avail and changed out the filters just in case.

I finally replaced all the fuel lines from the tank to the fuel pump and the problem went away. Once hoses get hard they tend to start leaking at the fittings. Cutting the ends off and reinstalling should temporarily solve the problem but with hoses that old your better off replacing them.

Are you the original owner? I ask only because that pick-up tube looks home made. Someone was trying to get the very last pint of fuel out of the tank. Mine was a rigged with a heavy walled aluminum pipe with roughly a 5/8? bore and a screen on the bottom. There is maybe 1/2" between the bottom of the pick-up and the bottom of the tank.

 

[capnrobalo]

Re: fuel starvation - pickup tube or other problem?

Thanks for the reply. I am not the original owner so I don't know the complete history of the boat. As for replacing the fuel lines, I am not opposed to it but my experience with this problem is that it occurs only after a full day of running around and only on rough seas. Even when the seas are rough and I leave in the morning with a full tank of fuel, I have zero engine problems. But, on the way back in I tend to have this problem. Last year I thought the mechanic had finally fixed it because I didn't have the problem all year. But, thinking back on my trips - the seas were always calm. I took the boat out last weekend and lo and behold the problem occurred on my ride back in about 10 miles offshore.

My hypothesis is that the lower level of fuel sloshing around in rougher seas allows the pickup to draw air out of the tank instead of fuel and over time enough of this air collects in the priming bulb. Once this happens and I hit a large enough wave the engine gets starved of fuel.

It is probably difficult to tell from the picture, but I just measured and the pickup tube is about 44 inches long. I wonder if it is hitting the front of the tank and curving upwards because of that?

 

[bhammer]

Re: fuel starvation - pickup tube or other problem?

Are you able to see in the tank? Do you any baffells in there? If you cannot remove it, then you could try shortening the brass pickup tube and adding a foot or two of gas safe tubing to the end with a brass pickup at the end. This will allow the pickup to slosh with the fuel.

I don't know if this is safe / legal for boats or will even work. This is what's done in some aerobatic aircraft though to make sure the pickup is always with the fuel, even while inverted. Inverted isn't good for boats though.

Just a thought....

 

[capnrobalo]

Re: fuel starvation - pickup tube or other problem?

I am not able to see in the tank to see if there are any baffles. And I realized it is probably difficult to tell from the photos in my first post, but the pick-up tube is actually plastic or nylon - not brass. And the barb fitting on the end is also plastic. I am trying to figure out why the barb fitting is even there in the first place. It doesn't seem to serve any purpose in my case. Maybe originally there was a screen or something attached but the previous owner may have removed it when he added the external Racor water separator. I don't really know. I would like to just replace the pick-up tube with a proper one but I'm not sure which one is proper or where to acquire it.

Oh, and I do like to keep my boat T-top side up... =) Thanks.

 

[dingbat]

Re: fuel starvation - pickup tube or other problem?

As for replacing the fuel lines, I am not opposed to it but my experience with this problem is that it occurs only after a full day of running around and only on rough seas. Even when the seas are rough and I leave in the morning with a full tank of fuel, I have zero engine problems. But, on the way back in I tend to have this problem.

You may have other problems but those where my symptoms to the tee. Only happened in rough water and only when my tanks where getting low. It didn?t matter if I was running off the main tank or off the reserve tank.

 

[bhammer]

Re: fuel starvation - pickup tube or other problem?

I am not able to see in the tank to see if there are any baffles. And I realized it is probably difficult to tell from the photos in my first post, but the pick-up tube is actually plastic or nylon - not brass. And the barb fitting on the end is also plastic. I am trying to figure out why the barb fitting is even there in the first place. It doesn't seem to serve any purpose in my case. Maybe originally there was a screen or something attached but the previous owner may have removed it when he added the external Racor water separator. I don't really know. I would like to just replace the pick-up tube with a proper one but I'm not sure which one is proper or where to acquire it.

Oh, and I do like to keep my boat T-top side up... =) Thanks.

Okay, if it is nylon, then it may be ard and not doing the job is should be doing. I think that brass thing you are talking about is the clunker which keeps the fuel pickup where the fuel is going. I'd try to find a new hose and see if that helps.

 

[capnrobalo]

Re: fuel starvation - pickup tube or other problem?

Ok, so my brother came by this afternoon and we got a lot accomplished with regard to the fuel pick-up. It has been like CSI Robalo trying to figure out what the previous owner(s) did to this fuel system and why. But, some answers are starting to fall in place.

I removed the sending unit this afternoon so I could have a better look into the tank. I noticed that there is a rigid aluminum tube that goes from the top of the tank (right next to where I removed the pick-up tube) and curves down out of sight towards the rear of the tank. I was able to reach it with a screwdriver through the sending unit hole and push it over enough to realize that it was at one time welded to the hole where I removed the pick-up tube (I'm calling this the withdrawal hole from here on out). Looking through the withdrawal hole, I could see that this aluminum tube has a nylon tube in the middle of it. I'm really getting confused at this point but definitely realizing that the pick-up tube that I removed earlier was not original equipment - at least not in that form. To make a long story shorter, my brother was able to remove the nylon tube from the aluminum tube. It is the short bit in the attached picture. It turns out that this short bit of tube used to be part of the pick-up tube that I removed yesterday. But, for some reason it was cut off and left in the top of the aluminum tube (see picture). I'm sure none of this makes sense to anyone still reading but it is helping to explain the problems I've been having. So I have a couple of questions:

1. Why is there a brass barb fitting with threads on the short bit of nylon tube that we removed today? How in the world could those threads be turned into something at the end of the aluminum tube in the tank? And what would it be? A filter? Anti-siphon valve?

2. Why did someone cut the original aluminum tube and push it aside? I'm guessing that a previous owner was having issues and tried to remove the pickup but failed because it got stuck in the aluminum tube. So he decided to just cut the aluminum tube and push it aside in order to get back into the main tank area. Drastic. Anyway, at least I decided that my tank does have a baffle of sorts and I think the aluminum tube runs through it to the rear of the tank. Good news.

3. What kind of fuel problem were they running into to take such a drastic measure as cutting the aluminum tube?

I stuck a length of vinyl tubing down through the aluminum tube until it stopped. I was able to draw fuel and blow bubbles into the fuel tank so it doesn't seem to be clogged or blocked by anything. At least that's a good sign.

Well, I'm off to bed to dream about what the hell someone might have been thinking when they rigged up my current situation. I doubt I'm gonna ever know the answer.

If anyone has more suggestions or possible explanations I'm happy to hear them.

 

[pine island fred]

Re: fuel starvation - pickup tube or other problem?

Will admit I got a bit lost on your post. Have only seen straight pickup tubes, Inside the tubes are often a finger filters, cone shaped fine mesh screen. If you can, push it up out of the tube from the bottom using a welding or brazing rod, maby even a coat hanger. They tend to get very clogged and a lot of people dont know they are there. regards FRED

 

[Bondo]

Re: fuel starvation - pickup tube or other problem?

Ayuh,....

Vinyl Tubing has a tendency to Float.....
The brass fitting was probably just an Anchor to keep the end down in the gas.....

By the looks of the Tank in the 1st picture,.... It's in need of Replacement......

 

[capnrobalo]

Re: fuel starvation - pickup tube or other problem?

For anyone interested, here is an email correspondence of my hypothesis for what happened to this fuel pick-up system.

Here is what I found out: below the withdrawal port on the top of the tank there is an aluminum guide tube that extends downward and then curves towards the rear of the tank. I had not yet seen this tube when I sent you my first email because it was pushed aside and not directly below the withdrawal port. I only found it by removing the fuel sending unit which mounts next to the withdrawal port and then I could see inside the tank better. The aluminum guide tube that I found looks like it used to be fixed (welded) to the top of the tank. But, it is no longer fixed at the top of the inside of the tank. The other end of this tube is fixed to the tank somehow but I can't see it. I believe that it probably goes through a baffle and then to the rear of the tank.

Now, inside this guide tube we found part of a nylon tube that was cut off even with the top. In the attached photo (0000), you can see I'm using a screwdriver to pry the aluminum guide tube so that it sort of lines up with the withdrawal port. Then in photo 0003, you can see the aluminum guide tube and the top of the nylon tube inside it. For scale, the guide tube is about 1" diameter and the nylon tube is about 3/8". The nylon tube was stuck in there pretty good, but with persistence we managed to remove it. It was about 5" long with a brass barb fitting on the end with threads. You can see it in picture 0007 (the short piece on the left). The piece on the right is the pick-up tube that I sent you a picture of previously.

After removing the short bit of tube, I realized what had happened in this boat's past. My hypothesis is this:

The nylon tubes that we removed used to be 1 single tube that ran through the guide tube. The brass fitting on the end of the short one is an anti-siphon valve. I only realized this was an anti-siphon valve this morning when my brother found a picture of one as I was typing this email. The aluminum guide tube used to be fixed to the top of the tank in order to guide the nylon pickup tube to the correct spot at the bottom of the rear of the tank (likely through a baffle). So, one of the previous owners probably had an issue with fuel pickup and tried to remove the nylon pick-up tube. However, I think they got it most of the way out and could not get the last 5 inches or so because it was stuck in the bend of the guide tube. They gave up and decided to cut the nylon tube - leaving the 5 inch piece at the top of the aluminum tube where it was stuck. But, now they needed a way to get a new pick-up tube to the main part of the tank so they cut the aluminum guide tube and pushed it aside. Amazing. I don't even know how they got a tool in there to do it - maybe a rotary tool from the inside of the tube? Anyway, they reused the long bit of nylon tube (about 44") and added a brass barb fitting for weight and basically just stuck it down in the main part of the tank (not going through any baffles or anything).

It is very easy for me to see how this setup caused the fuel starvation symptoms I've been having. The nylon pick-up tube could easily flop around in rough water and with a low fuel level it was probably sticking in the air quite a bit. Not to mention that there was no longer an anti-siphon valve until last year when my mechanic discovered that I did not have one. He added one between the withdrawal fitting and the hose that runs to the motor. He didn't realize that I actually did already have one but it was just not in use and stuck at the top of an aluminum tube that he didn't even know existed. Oh well.

I believe that all I need to fix this problem is to find a 48 inch length of the proper nylon pick-up tubing and stick it down through the guide tube. I will try to somehow make the guide tube fixed again so that it can't sway and possibly pinch the nylon tube that runs through it.

Thanks for the help everyone. As soon as I find a replacement pick-up tube I will be on my way to fixing this problem for good.

Jason

 

[capnrobalo]

Re: fuel starvation - pickup tube or other problem?

I received the fuel tank drawing from the tank manufacturer and confirmed my suspicions that a previous owner had cut the pick-up guide tube in the fuel tank. I'll never know what problem might have caused him to do this but some things go unexplained. The nylon pick-up was then just dropped down into the main part of the tank between a baffle in the front and a baffle in the back. This completely bypassed the guide tube which was intended to guide the nylon pick-up near to the tank floor and through the rear baffle to the rear of the tank where it would likely get fuel at all times.

I've got a new nylon pick-up on order now and once installed hopefully that will be the end of this problem for good.

I still need to figure out how to secure the guide tube so it can't sway and pinch the new nylon pick-up running through it. I was thinking of using some type of cold-weld (there is still some fuel in the tank and I'm not planning on removing it to fix this problem). Any suggestions for this repair?

 

[capnrobalo]

Re: fuel starvation - pickup tube or other problem?

Fail. I took my boat out last weekend after installing the new pickup tube inside the guide tube. The problem occurred after I burned about 30-40 gallons of fuel. After limping back in as usual with my brother priming the bulb constantly, I left the boat docked overnight. In the morning, the problem was still there and went away immediately after I filled up with fuel at the marina. This is very frustrating.

 

[jeeperman]

Re: fuel starvation - pickup tube or other problem?

An earlier post stated the long nylon tube went to the front of the tank. Did you put the new tube down thru the alum. tube?
Are you sure the alum. tube is only a guide tube?
Is it possible that the alum. tube was the original pickup tube?
The draw port appears to have pipe threads on the outlet. From your pics it would appear that your sticking the nylon tube thru the treaded port and it is open to atmoshere i.e. your not utilizing the port threads to seal?

I suspect that maybe the alum. tube was the pickup tube with a screen or anti-siphon valve on the end. At some point in it's life a crack developed in the tube where it is welded to the underside of the tank/outlet fitting. Being aluminum, this is not unheard of. The crack allowed the engine to suck air from the tank and get the symptoms your having now.
So the previous owner tried to fish a nylon tube down the alum. tube as a fix. The piece you fished out was the remainder of that aborted attempt.
So with the aported piece seemingly wedged in the alum. tube they moved on.
They managed to cut the alum. tube off of the tank or wiggled it enough that the rest of the weld broke and then pushed it aside. They then put in the nylon tube next to the alum. tube but the baffle is built around the alum. tube and that is the only way to get to the rear most part of the tank.

You installed the new nylon tube inside the old alum. pickup tube. Which might have a screen and/or anti-siphon valve still on the end of it. Both of which might not flow like they did when new. And might have been why the alum. tube was bypassed.

So now your new nylon tube is down there trying to suck fuel with those obstacles in the way. With a full tank and until you burn off the 30-40 gallons or so, that fuel creates just enough static pressure (head) to force enough fuel past the old pickup line obstacles. Without the 30-40 gallons of fuel head in the tank and fuel sloshing around, there is less fuel head in your tank.

I would try placing your new line next to the alum. line again.
You might also use a dental mirror and try to see if there are any openings between the baffle(s) and floor of your tank. If there is try to get the new tube thru one of those passages and as far to the rear of the tank as possible.

Then seal around the new tube and the threaded outlet port so you are not getting fumes out of the tank.

And make sure your tank vents are clear as drawing 30-40 gallons out of a tank without venting will get a vacuum lock and starve you too.

 

[capnrobalo]

Re: fuel starvation - pickup tube or other problem?

An earlier post stated the long nylon tube went to the front of the tank. Did you put the new tube down thru the alum. tube?
Are you sure the alum. tube is only a guide tube?
Is it possible that the alum. tube was the original pickup tube?
The draw port appears to have pipe threads on the outlet. From your pics it would appear that your sticking the nylon tube thru the treaded port and it is open to atmoshere i.e. your not utilizing the port threads to seal?

Thanks for the response. Attached is the fuel tank drawing that I got from the manufacturer. It has a note that it was redrawn in 2001 so I am not sure what might have changed on this drawing since my tank has been in the boat since 1996.

To answer your questions, I believe the aluminum tube is only a guide tube (also indicated in the drawing). The new nylon pickup I received from the tank manufacturer had an "ell" fitting on one end and a small screen on the other end. I removed the screen and put this tube down in the guide tube and threaded the fitting onto the withdrawal port. The nylon tube I received was not exactly the right length according to the drawing so I had to cut it in order for it to fit all the way into the tank and allow me to thread the fitting.

So now your new nylon tube is down there trying to suck fuel with those obstacles in the way. With a full tank and until you burn off the 30-40 gallons or so, that fuel creates just enough static pressure (head) to force enough fuel past the old pickup line obstacles. Without the 30-40 gallons of fuel head in the tank and fuel sloshing around, there is less fuel head in your tank.

I don't quite understand what you mean by static pressure. Can you explain that in more detail?

I would try placing your new line next to the alum. line again. You might also use a dental mirror and try to see if there are any openings between the baffle(s) and floor of your tank. If there is try to get the new tube thru one of those passages and as far to the rear of the tank as possible.

I did use a mirror and I don't see any way past the baffle other than going through the guide tube. And, there does not seem to be much clearance at all between the bottom of the baffle and the bottom of the tank floor, i.e., not enough for even the nylon pickup to go between.

And make sure your tank vents are clear as drawing 30-40 gallons out of a tank without venting will get a vacuum lock and starve you too.

I will check the tank vent because that is something I have not yet done. While the boat was exhibiting this problem last weekend, I did remove the pickup tube entirely from the tank while I was offshore. This would have cleared any vacuum lock that possibly existed. Then after putting the pickup tube back in the boat ran fine for about 10 minutes. Is the "vacuum" lock the same thing as "vapor" lock?

Thank you very much for your analysis of the problem. My boat is currently in Orange Beach and I'm in Atlanta so I can't try anything right away. If you have any more ideas given the new information please let me know. Thanks!

 

[DRIFTER_016]

Re: fuel starvation - pickup tube or other problem?

How long was the new tube.
According to the diagram it should be either 46" or 48" my old eyes can't tell from the drawing. Unless it was over 5 feet long it should have fit without cutting it. In fact 5 feet would put the end of the pickup 2" to 3" from the back of the tank. I gather that the tank is length wise with the pickup running aft right?

Make sure your vent is clear. Disconect it at the tank and blow into the hose. If there is any blockage you'll know.

I was having issues this spring when I installed a new primer bulb, it would collapse under WOT and starve for fuel while fouling the plugs with oil.

 

[capnrobalo]

Re: fuel starvation - pickup tube or other problem?

How long was the new tube.
According to the diagram it should be either 46" or 48" my old eyes can't tell from the drawing. Unless it was over 5 feet long it should have fit without cutting it. In fact 5 feet would put the end of the pickup 2" to 3" from the back of the tank. I gather that the tank is length wise with the pickup running aft right?

Because the .PDF was too big I had to take a screenshot of it so I could create a smaller .JPG to post it on here. The number you are referring to from the drawing is 46" not 48". The new pickup tube was 56", not including the fitting on the end. I can't remember how long it was with the fitting. I have a feeling it was just what the manufacturer had on hand and not "exactly" the original part. Plus, I noticed that the drawing was redrawn in 2001 so I can't trust it completely.

I was having issues this spring when I installed a new primer bulb, it would collapse under WOT and starve for fuel while fouling the plugs with oil.

I guess I'll need to inspect the plugs too once I finally fix this problem ... Thanks for the help.

 

[jeeperman]

Re: fuel starvation - pickup tube or other problem?

I don't quite understand what you mean by static pressure. Can you explain that in more detail? Thanks!

Your fuel tank is like a gravity pressurized water tower in that when it is full there is more water pressure. The more you draw down the less pressure there is. You might have a fuel pump weakness due to wear problem that does not show up until the fuel load (pressure) in your tank goes down.
If your fuel tank was mounted higher than your engine, you could run without the fuel pump if not fuel injected model.

I am about 20 miles from your boat. If you have a need for someone to go check on something let me know.