Found fuel problem, now how do I fix it?

Shrek · #1 11-22-2011, 01:31 PM

First, I cannot remove the tank without ripping off the deck, plus it is glassed into the stringers.

The boat runs fine in the morning but as the fuel burns off, performance suffers. The boat surges under power; on plane I see 400-600 rpm surges, i.e. running at 4000 RPM and the boat will momentarily drop to 3400 RPM and then go back to 4000 RPM. There is no dramatic cut out (I don't think that it is electrical) with this but more like a gentle surge and it happens over and over again.

I drained the tank and pulled the fuel sender to have access to the tank. The rear most chamber was fairly clean and I was able to clean it out pretty well using my fuel polishing rig. I looked into the tank with a borescope and found that the inside of the tank looks pretty good. There is a bit of corrosion on the top of the tank, but nothing serious; it is mostly shiny metal.

Problems.

1. The fuel pickup looks to be less than 1/16 of an inch from the floor of the tank. Does this need to be higher? If so, how high?

2. The chamber beyond the first baffle has all kinds of large varnish chunks that I cannot reach with my siphon. Is there any chemical that will actually dissolve that stuff? Seafoam? Startron?

smokeonthewater · #2 11-22-2011, 02:08 PM

how bout a mesh strainer of some sort on the pickup? just fine enough that anything that makes it through will easily pass through the fuel line to the filter.... would be a bandaid fix but you could use the fuel polishing rig from time to time as the gunk gradually got broke loose

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spareparts · #3 11-22-2011, 08:30 PM

I would expect the fuel pick up to be higher off the floor, simple solution, pull it out and cut the end at an angle, that way it won't suck itself to the floor. Use some acetone in the tank to try and break up the varnish. BTW, I can't remember if I've asked this before, do you have the grey mercury fuel hose on the engine? If you do, cut a short section off, split it and turn it inside out, you'll be surprised at what you find

smokeonthewater · #4 11-22-2011, 08:53 PM

I've been thinking about this today.... You asked what would clean the tank and I think that your problem is just the opposite of what you are thinking.... for years that tank had pure gasoline in it and has managed to get gunked up... now in recent years E-10 has found it's way throughout the country and even into most marina's.... E-10 actually does a pretty good job of breaking up the varnish and gunk in the tank.... I suspect that it is doing just that and thus you are now having issues....

I also was thinking of another option for an in tank screen that wouldn't let the gunk just fall back onto the tank.... An inline fuel filter containing a pleated element with the inlet opened up to about 1/2" would stop the crap from fouling your fuel line but it would trap it so that you would eventually get it out of your tank...

Shrek · #5 11-23-2011, 02:05 AM

Quote:

Originally Posted by spareparts

I would expect the fuel pick up to be higher off the floor, simple solution, pull it out and cut the end at an angle, that way it won't suck itself to the floor. Use some acetone in the tank to try and break up the varnish. BTW, I can't remember if I've asked this before, do you have the grey mercury fuel hose on the engine? If you do, cut a short section off, split it and turn it inside out, you'll be surprised at what you find

How high should the pick-up be off the floor and/or how much of an angle? Will acetone screw up the motor if there are remnants in the tank? All the fuel line is the new ethanol approved heavy duty marine stuff, the black hose.

Quote:

Originally Posted by smokeonthewater

E-10 actually does a pretty good job of breaking up the varnish and gunk in the tank.... I suspect that's why you are having issues....

I also was thinking of another option for an in tank screen that wouldn't let the gunk just fall back onto the tank.... An inline fuel filter containing a pleated element with the inlet opened up to about 1/2" would stop the crap from fouling your fuel line but it would trap it so that you would eventually get it out of your tank...

So are you thinking that I should just leave the tank full of E-10 and let chemistry do it's thing? I'm not sure what you're thinking about a screen? I have a good spin on filter separator and that is where I want the chunks to end up. I would think that a screen would cause the stuff to remain in the tank which is the opposite of what I want.

smokeonthewater · #6 11-23-2011, 02:33 AM

well yeah but we need to figure out what is stopping the engine from running right.... the filter/separator being plugged wouldn't come and go.... once it was plugged you'd be done till you put a new one on.... I was thinking that you might be getting big enough chunks of crud to plug the line.... if the crud stays in the tank and slowly dissolves over a couple years but doesn't effect the engine then it's no biggy but if it is making your engine run lean you are in a bad way. maybe your fuel pump on the engine is dying.... when it starts running poorly does the squeeze bulb collapse?

Have you tested with a portable tank?

the pickup does not need to be any specific distance from the bottom but it wouldn't hurt to raise it 1/4" or so too make sure it isn't touching. You may be able to simply bend the tube a little.... just remember that the higher you go the further you have to swim LOL

BTW you need to NOT be running the engine lean.... if it is losing power from lack of fuel you are almost definitely doing damage.... Lean is hot.. hot causes detonation... detonation destroys pistons and destroyed pistons destroy cylinders

might take hours or might take seconds