Gents I have been working on my 91 Marlin. Last fall I found my port motor was starving for fuel on the main tank. The issue exists from the tank to the valve switch. Pulled floor yesterday the elbows are welded on main tank threaded on aux. All hoses are good, Haveing little experience in the fuel tanks what should I expect to get into. Tanks have no rust so would like to work with what I have. Thxs.
gas tank marlin
- Thread starter GreatWhite23
- Start date
I guess I've never looked at my fittings close enough, but are you sure that the pickup fitting is welded? The fuel fill is usually welded, but usually a fuel pickup fitting is screwed in?
So, if you're 100% sure that the fuel selector switch is good and the fuel line from the switch to the tank is good, then that leaves either the tank itself or the pickup tube. But we can eliminate the tank since if that was the problem, you'd have a bilge full of fuel and I'll assume you'd pick-up on that! :mrgreen: So that leaves either the tank fitting or the pickup tube - broken or a crack that is allowing air in.
Do you have another fitting available on the tank? Maybe one that is currently plugged? You could convert that one to your pickup. But first, you can verify if that's the problem --
-- Remove the fuel pickup line from it's current fitting
-- Lengthen the fuel line with a hose barb and more fuel line
-- Remove either another tank fitting or even the fuel fill hose (check to see if there's a bar in the fuel fill fitting to prevent siphoning)
-- Stick the "new" hose into one of those places to create a new fuel pickup
-- Prime and run the engine
If you don't feel the "new" fuel line is going in straight enough (curling up), attach it to a length of PVC pipe with some basic fittings that you can find at Home Depot to transition from the pipe to a barb.
So, if you're 100% sure that the fuel selector switch is good and the fuel line from the switch to the tank is good, then that leaves either the tank itself or the pickup tube. But we can eliminate the tank since if that was the problem, you'd have a bilge full of fuel and I'll assume you'd pick-up on that! :mrgreen: So that leaves either the tank fitting or the pickup tube - broken or a crack that is allowing air in.
Do you have another fitting available on the tank? Maybe one that is currently plugged? You could convert that one to your pickup. But first, you can verify if that's the problem --
-- Remove the fuel pickup line from it's current fitting
-- Lengthen the fuel line with a hose barb and more fuel line
-- Remove either another tank fitting or even the fuel fill hose (check to see if there's a bar in the fuel fill fitting to prevent siphoning)
-- Stick the "new" hose into one of those places to create a new fuel pickup
-- Prime and run the engine
If you don't feel the "new" fuel line is going in straight enough (curling up), attach it to a length of PVC pipe with some basic fittings that you can find at Home Depot to transition from the pipe to a barb.
Thanks Dennis,
I am sure they are welded the Aux tank is screwed, there are no other plugs in the tank. Thinking about threading a new port for pick up but am afraid of metal shavings.
I am sure they are welded the Aux tank is screwed, there are no other plugs in the tank. Thinking about threading a new port for pick up but am afraid of metal shavings.
Well, in addition to the shavings, I think you would first need to weld a thicker plate to the tank before tapping threads. You won't be able to tap threads into the main part of the tank - way too thin. Unless there's already a bossed area? You "should" be able to drill/tap and keep the shavings out of the tank by using grease on your bits. But of course there's no guarantees.
Although your fuel filters should eventually catch the shavings (add another inline filter, if you want), you obviously won't be able to weld with the tank in the boat (with gas in it, anyways). Since it'd be easiest to remove all (and I mean ALL) the fuel and rinse it out and get rid of fumes by taking the tank out of the boat, I would go that route (removing tank)... Pump the gas over the aux tank, and then into containers (even a clean garbage can will do) and into your cars.
Although your fuel filters should eventually catch the shavings (add another inline filter, if you want), you obviously won't be able to weld with the tank in the boat (with gas in it, anyways). Since it'd be easiest to remove all (and I mean ALL) the fuel and rinse it out and get rid of fumes by taking the tank out of the boat, I would go that route (removing tank)... Pump the gas over the aux tank, and then into containers (even a clean garbage can will do) and into your cars.
Mr. Greatwhite 23,
I'm working on the same issue on the same boat and know this subject very well. I actually need some info from you if you don't mind.
You didn't ask much of a question except what should you expect to get into. The answer is a big #$#$# mess if you snap the 90 degree fitting off of the top of the tank. This is where I stopped and had to weight my options because I can't comfortable rotate the antisyphon valve out of the 90 degree fitting. I'm working from the fuel selector valve back to the tank. If I have to remove the barb from the 90 fitting I'll build something that holds that 90 tighter than a vise.
I assume you have Florida Marine tanks? They drill a hole in the tank then weld in a round threaded fitting. Some of these fittings are welded so ugly that the fitting is hard to see. Now, you're looking at it so you know best. Maybe someone else broke it and had to weld it. Not sure this is an issue though. If the 90 degree fitting is stainless it's not welded to an aluminum tank.
You can NOT remove the pick up tube from the tank. Look down the fuel sender hole and you'll see the bottom of the pick up tube is welded to a piece in the tank
You problem could be:
out of fuel if the forward pick up is going to port
Hole/crack in pick up tube
Leak at top of the tank fittings
Plugged up antisyphon valve
Bad fuel line
Plugged up fuel switch.
Dennis has a good idea about the fuel line test but don't use a fuel barb to lengthen the hose. You'll starve the fuel hungry 250HP because the ID of the barb is too small. .
Did you try swapping hoses on the main tank to see now if the stb engine dies and port is OK?
***Can you please look on your Florida Marine tanks and give me some info off of the ID decal? Can you read the tank model number, capacity, lot number, gauge thickness and year MFG? This info is listed on the bottom of the decals.*** Thanks, this info will help us both. I can only read some of this info on mine due to the labels being all messed up.
I'm working on the same issue on the same boat and know this subject very well. I actually need some info from you if you don't mind.
You didn't ask much of a question except what should you expect to get into. The answer is a big #$#$# mess if you snap the 90 degree fitting off of the top of the tank. This is where I stopped and had to weight my options because I can't comfortable rotate the antisyphon valve out of the 90 degree fitting. I'm working from the fuel selector valve back to the tank. If I have to remove the barb from the 90 fitting I'll build something that holds that 90 tighter than a vise.
I assume you have Florida Marine tanks? They drill a hole in the tank then weld in a round threaded fitting. Some of these fittings are welded so ugly that the fitting is hard to see. Now, you're looking at it so you know best. Maybe someone else broke it and had to weld it. Not sure this is an issue though. If the 90 degree fitting is stainless it's not welded to an aluminum tank.
You can NOT remove the pick up tube from the tank. Look down the fuel sender hole and you'll see the bottom of the pick up tube is welded to a piece in the tank
You problem could be:
out of fuel if the forward pick up is going to port
Hole/crack in pick up tube
Leak at top of the tank fittings
Plugged up antisyphon valve
Bad fuel line
Plugged up fuel switch.
Dennis has a good idea about the fuel line test but don't use a fuel barb to lengthen the hose. You'll starve the fuel hungry 250HP because the ID of the barb is too small. .
Did you try swapping hoses on the main tank to see now if the stb engine dies and port is OK?
***Can you please look on your Florida Marine tanks and give me some info off of the ID decal? Can you read the tank model number, capacity, lot number, gauge thickness and year MFG? This info is listed on the bottom of the decals.*** Thanks, this info will help us both. I can only read some of this info on mine due to the labels being all messed up.
The fuel pickup is welded? Well, I suppose that's a good idea... until it needs to be replaced :bang Would you be able to reach in there through the sender and either cut it (or the thing it's welded to)? Or maybe use a small (palm) hacksaw?
Regarding the fuel barb thing... wouldn't the ID be basically the same as the other barbs already in use? Fuel selector, fuel filter, etc.
Anti-siphon valve clogged up - that's a good thought. Seeing as the pickup tube is aluminum, I would lean towards the valve being the culprit before anything else. I still find it strange that the fitting is welded in, but like Distraction said, you're there looking at it. IF it turns out that you can just screw it out, swap it with the aux tank's valve. I've never messed with trying to fix one (don't even know if it can be reliably done) - just replace it. I seem to recall a "test" for them involving putting a long tube on it and seeing how many inches of water (basically weight) it can hold back - but that's going back a long, long time!
Regarding the fuel barb thing... wouldn't the ID be basically the same as the other barbs already in use? Fuel selector, fuel filter, etc.
Anti-siphon valve clogged up - that's a good thought. Seeing as the pickup tube is aluminum, I would lean towards the valve being the culprit before anything else. I still find it strange that the fitting is welded in, but like Distraction said, you're there looking at it. IF it turns out that you can just screw it out, swap it with the aux tank's valve. I've never messed with trying to fix one (don't even know if it can be reliably done) - just replace it. I seem to recall a "test" for them involving putting a long tube on it and seeing how many inches of water (basically weight) it can hold back - but that's going back a long, long time!
The tank is 21.5" deep and the pick up tubes are about 20"+ long. At that length vibration and sloshing fuel would snap the tube off if they were not wasn't weld at the bottom. It's a well built tank.
Can't reach in and cutting inside a gas fumed tank is an issue.
I think the tube should not be at the top of his hit list. Fill tank with fuel and test run it, that'll tell you.
Swap the lines at the tank and tell me what happens.
Can't reach in and cutting inside a gas fumed tank is an issue.
I think the tube should not be at the top of his hit list. Fill tank with fuel and test run it, that'll tell you.
Swap the lines at the tank and tell me what happens.
21"? Good point - I didn't realize the tank was that deep.
And, no, I wouldn't advocate cutting the sender until the tank has been removed and thoroughly evacuated of all gas and fumes (cleaned and turn upside down). But if you can't reach it, doesn't much matter.
I suppose there's more than one way to diagnose this, but I would hesitate to fill the tank -- if, by chance, there was a crack at the very top of the tube, one might then wrongly assume the tube is OK and the problem is elsewhere. In other words, the crack would have to be below the level of the fuel - which it might be, but it's hard to tell. But then, if that fuel pickup and anti-siphon is welded, that really cuts down on the "easy" diagnosis options.
How about going in there with a snake camera? It may or may not show anything, but it's an easy step and may be worth the few minutes that it would take. If you don't have one, they've really come down in price lately -- and it's good tool to have around the house. And... be real... how much of a reason do we really need to buy a new tool? That right there is about 5x as much of a reason as I would need!
And, no, I wouldn't advocate cutting the sender until the tank has been removed and thoroughly evacuated of all gas and fumes (cleaned and turn upside down). But if you can't reach it, doesn't much matter.
I suppose there's more than one way to diagnose this, but I would hesitate to fill the tank -- if, by chance, there was a crack at the very top of the tube, one might then wrongly assume the tube is OK and the problem is elsewhere. In other words, the crack would have to be below the level of the fuel - which it might be, but it's hard to tell. But then, if that fuel pickup and anti-siphon is welded, that really cuts down on the "easy" diagnosis options.
How about going in there with a snake camera? It may or may not show anything, but it's an easy step and may be worth the few minutes that it would take. If you don't have one, they've really come down in price lately -- and it's good tool to have around the house. And... be real... how much of a reason do we really need to buy a new tool? That right there is about 5x as much of a reason as I would need!
GreatWhite23 said:
Starving can be two things, not enough fuel or too much air
To see which it is, you would check the primer bulb when the motor starves to see if it collapses or not. If it doesn't collapse, you are sucking air and assuming there are no leaks, the pickup tube is broken.On the other hand if the primer does collapse, then there is a blockage somewhere. That could be as simple as a piece of gunk plugging the pickup screen or tube. Blowing air carefully into the tank might help but keep in mind that there should be an anti-siphon valve in the feed and that normally wont allow air or fuel to flow back. A bad anti-siphon valve is a fairly common cause of fuel starvation. The valve would not be welded or brazed to the pickup but would be threaded into the pickup fitting. It can look exactly like a standard elbow or straight fitting.
i agree on changing the anti syphon valve first. to the op, an antisiphon valve looks just like a normal brass threaded barb fitting on your 90 degree tank elbow but is slightly longer than a normal fitting. it has a ball valve inside that can get stuck.
it is very hard to tell that the 90 degree elbow on top of my (much smaller) florida marine tank is actually threaded into the tank, but it is. as another distraction noted, there should be a threaded aluminum boss welded to the tank with the elbow screwed into it, because the 90 degree elbow is not aluminum and the tank is aluminum.
also, i can't speak for the marlin tank but normally they will weld an aluminum tube with a cutaway at the bottom into a fuel tank that supports a removable pickup tube that fits inside it. the inner pickup tube should come out no problem if you remove the 90 degree fitting.
it is very hard to tell that the 90 degree elbow on top of my (much smaller) florida marine tank is actually threaded into the tank, but it is. as another distraction noted, there should be a threaded aluminum boss welded to the tank with the elbow screwed into it, because the 90 degree elbow is not aluminum and the tank is aluminum.
also, i can't speak for the marlin tank but normally they will weld an aluminum tube with a cutaway at the bottom into a fuel tank that supports a removable pickup tube that fits inside it. the inner pickup tube should come out no problem if you remove the 90 degree fitting.
Thx I will send info you are looking for if mine is readable anotherdestraction. The motor would run out of fuel, 2-3 minutes restart and get another 4-5 miles.... repeat process. Changed fuel filters symptoms got alot better then got alot worse.Run on aux and they run 100%. My goal is to have the boat ready to return to the coast in early April. I have a long list that seems to be growing. A new tank is 1,200??? I might go that way but would rather not. Thank you for your help. There are four lines two paired(same size)would be the pickup two other paired would be the anti syphon and fill???
There are 4 lines per tank. Two towards bow and two towards stern.
The bow lines are fill and vent.
The stern are the two pick ups with anti syphons. These lines are the same size. (Google / you tube antisyphon. Its a barb with a ball and spring in it. Simple.)
Do not buy a new tank. You'll be fine.
Marlins don't have primer balls. They have primer pumps.
The bow lines are fill and vent.
The stern are the two pick ups with anti syphons. These lines are the same size. (Google / you tube antisyphon. Its a barb with a ball and spring in it. Simple.)
Do not buy a new tank. You'll be fine.
Marlins don't have primer balls. They have primer pumps.
Agree with above - don't fret about a new tank. You're dealing with a problem with a component of the tank, not the whole tank. Other than some time and effort, this shouldn't be a relatively cheap fix, assuming you can do most of it yourself. Even if you can't - it still shouldn't be too bad.
Thanks!
If you put a big adjustable wrench across the flats on the 90 degree fitting and loosen / remove it from the tank let me know how you make out and what you find.
If you put a big adjustable wrench across the flats on the 90 degree fitting and loosen / remove it from the tank let me know how you make out and what you find.