View Full Version : Fuel tank flush? Fuel deliver problems.

10-22-2007, 01:57 AM
I seem to be having a fuel delivery problem. I am suspecting recurrent blockage in the fuel tank fuel line pickup. Details and symptoms:

Midsummer, had fuel supply problems. Old mercury type filter cannister was full of goopy creamy emulsion, and about a teaspoon of pale green dust. Replaced cannister - easy fix. I was pleased with myself.

More recently, fuel cutout problems. Electric pump seems to work well -it keeps ticking, indicating it is not ...filling the float bowl. Cannister was not full of fuel. Pump worked well with fuel line in a gerry can.

Cleaned fuel lines. Line from filter to tank is copper. Cleaned it, a few flakes of black came out. At tank is a high quality 3 position fuel valve - I expected it to be gummed up, but it was clean.

I took a big bike pump with a pressure gauge and pressurised the line into the tank. After building some pressure, it blew back into the tank. Motor then ran happily for 45 min. I was pleased with myself. Assumption - pick-up blocked.

But today, a week later, problem is back. The tank is monel, I believe, and ~40 years old. As noted, there is some pale green dust - some kind of insoluble nickel salt?

Is my tank bottom full of grit and other muck which will continue to block my fuel pickup? If so, how can I clean/flush/dissolve/fix my problem?


David Masury
10-22-2007, 06:39 AM
I had the same sort of problem a few years ago.... I replaced all rubber and copper lines from the tank through to the carburator. That helped a bit. I also made sure that the tank vent was clear and the tank was breathing.

Generally speaking monel tanks are very good and are very resistant to corrosion. When my boat was on land I drained the fuel tank overboard into five gallon containers.... then I purchased two gallons of alcohol from the hardware store... sloshed it around in the tank and let it set for a few hours..then syphoned out the alcohol through a paper coffee filter into another five gallon container... there was a lot of stuff in the filter... I reused the alcohol and repeated this procedure several times until there was nothing in a new paper filter. I refilled the tank with clean fuel and have had no problems since.

Do make sure that you can have the boat wide open and a breeze blowing when you do this...

Best of Luck,


10-24-2007, 12:20 AM
thanks for the tips Dave.

"Do make sure that you can have the boat wide open and a breeze blowing when you do this..."
I think I also shouldn't use a candle or oil lamp to illuminate the inside of the fuel thank - what do you think ? :)

10-24-2007, 07:54 PM

I had some fuel issues about two years ago. Not quite as bad as yours as I didn't have Green dusty junk .The boat is 1965 Pearson Vanguard with a Monel tank.

I mounted a new Raycor filter and a 12 volt fuel pump on small section of 2x12. I wired the fuel pump with extra long leads with bannana pugs on the end. I used a 12v power supply I had to power the pump. On the fuel filter goes on the suction side of the pump. What I did was pull dirty fuel from the bottom of the tank, filter it and return it back tothe tank to be cleaned again.

at first the filter would be full of water in about 5 minutes of turning on the pump. When the fuel flow started to slow a new filter was installed. It took a few evenings and about 5 filters to get everything cleaned up. From time to time I would hang out on the shrouds and rock the boat like crazy to stir up the fuel. When I could run the pump for an hour or so pumping 1 1/2 gallons per minute and still have a clean filter I called the job complete. In the end I removed about 3/4 gallon of water out of a 20 gallon tank that was 2/3 full.

Before this cleaning we only used about one tank full each season. I did this just before installing a Moyer Marine fresh water cooled rebuilt engine. Fuel problems on a new engine were the last thing I wanted. The new engine now has about 200 trouble free hours on it in two seasons of use. It would've been double that buy the boat spent 14 weeks on the hard this summer being painted. I try to run the engine for a least one solid hour each time I leave the dock.

Using the engine a lot and keeping the fuel filter clean is the best way to avoid fuel related problems.


10-25-2007, 05:37 AM

How did you return the fuel to the tank? Through the deck fitting?


10-26-2007, 12:58 AM
nice trick! I don't have a spare 12v pump around, but I may have to go find one.

10-26-2007, 04:52 PM
Yes I simply let the return line dump back into the deck fitting.
I picked up a cheap >$20 fuel pump off the shelf at the local auto parts store. I can't remember the brand but it's an unregulated generic fuel pump.


10-28-2007, 01:20 AM
I set out today to follow Mikes advice. I decided I'd try to pull fuel out the filler, hopefully capturing grit etc. Only trouble was, I couldn't get the hose down all the way to the fuel - odd, there was some sort of an obstruction, maybe an elbow...In any case, I then removed the valve at the outlet and pulled 5 gals out, using a hand plunger type pump. It pulled out well, no blockage, but there was a little sediment - not enough to cause alarm.

Now here's the odd thing: As I pulled the pump, the gas was foamy (I used a vinyl hose so I could see) and after each pull, a regular stream of big bubbles, about one /3", rose up the hose (see pic). That hose clamp is on tight, so I can only surmise that the pickup tube, inside the tank, is not airtight above the fuel line - can anyone think of a different explanation? Given notes on other threads about air leaks in fuel lines, this might explain my fuel delivery problems - too much air in line for the (electric) fuel pump (?).

If I'm right, its a pain, because the tank is under the cockpit floor and there's no easy way to get at it, or an inspection hatch- if there is one!

10-28-2007, 07:25 PM

What's with the string wrapped around the fuel fitting? It that something you've rigged up just so you could use the clear tubing for this cleaning operation? It looks like it's soaked with fuel. If you were using the string as some sort of filler so the larger clear line would fit, that's where your air is coming from.

When I cleaned my tank I didn't use the filter installed on the boat. A new one was purchased just for cleaning my tank. It wasn't until after the tank was clean that I pulled fuel through the boats fuel lines.

If you are seeing ANY air being pulled though the boats fuel lines you are correct in thinkng you have other problems. Any air is too much much


10-29-2007, 05:18 PM
Mike, thanks for your reply. Yes, any air in the fuel line is too much, I agree.

The string is unrelated, and was there before. The hose was, *I believe* very firmly attached to the tank spigot via the hose clamp, directly on the threads. That hose leads to a plunger type pump into a 5 gal can. And yes, pulling the plunger showed fuel foamy-with-air running up the vinyl hose, with big bubbles drifting up after each pull (as per photo). So it appears that the pickup line inside the tank, betwen the spigo and the bottom of the tank - is letting in air above the fuel line, its hard to imagine how that could happen, but anything's possible I guess.

What is usually on the end of the pick-up? I'm wondering it if had a non-return valve which I inadvertently blew whne blowing air back down the fuel line to clear a presumed blockage in the fuel line. There certainly wa a blockage, because I pumped up to about 40lbs before the pressure released into the tank! hmmm, could I have blown a hole in the pickup line? Unlikely, the whole boat is built to last, I assume its a monel or copper tube. ???

>When I cleaned my tank I didn't use the filter installed on the boat.

neither did I. I pumped directly into the jerrycan then filtered when going from can back to tank.


10-29-2007, 07:20 PM
i'm stumped....
40psi is a lot of pressure for sure something was really backed up. I had always assumed that there was some sort of bronze screen or something on the pickup tube but who knows. The builders may have used a check valve but I don't see the need for one. I do know that the pick up tube does not go all the way to the bottom of the tank. When I cleaned my tank I was only getting a tiny bit of water in the carb but I was still able to get almost 3/4 gallon of water out of the tank with my filter setup. it seems reasonable that the pickup is around 1" off the bottom.

Again, I find the string to be strange if not a little scary. It looks wet with fuel. If you put maybe 5psi of positive pressure on the fuel line (block of the vent) I wonder if the string would drip fuel. If so it will draw air if on the suction side. I know it's a stretch

If you can reach the fitting on the tank maybe you can remove the pick up tube. If you could i'm sure you would've alread done so.

you may be going down the road to removing the fuel tank . :(

10-30-2007, 04:12 AM

Just a thought, but you do mention tightening your hose-clamp on the "threaded" portion of the fuel tank outlet. Couldn't the spiral in the threads be letting air by the clamped connection, even if the clamp is tight? (or even let gas get wicked-out by the string?)

You never know...

And I second Mike's opinion about the string and the wet look of the connection. This area should be dry and clean for your safety and peace of mind.

Good luck! I'm looking at taking apart my cockpit in order to remove the gas tank- it's no longer reliable...


10-02-2008, 04:04 PM
I am wondering what kind of alcohol you were using?

Wood, isopropyl, single malt?

10-02-2008, 04:22 PM
I don't know how I missed this thread before, but that surely doesn't look like Coast Guard approved fuel line. More like water hose...

And the comments about the threaded portion.... Should be a hose barb. Maybe that's the point of the thread??? Trying to seal a connection that wants to leak?