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Gas Line Tar Dissolver


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I have a 574 gas that had sat for a dozen years or so. The gas lines were full of a black tar like substance. The people I got it from cleaned most of it out, except the main line that goes from the sediment bowl to the fuel pump. They got it to flow thru it, but I still get crap out of it.

I can run the tractor around no problem, but if I put it under a load at higher rpm, it is running out of gas. At this point I am guessing that there is still enough tar in the main line, that it is restricting gas flow.

If I let it set awhile, it will start up and be alright, until I push it again. When it shuts down, it will try to start if I choke it.

I really don't want to tear it apart to get the main gas line out right now. Is there anything that will dissolve this crap?

I will yank the carb again and make sure it has not partially plugged anything in there also.

I saw a video on u tube of a 574 diesel, that also had this black tar crap in it. Where does this stuff come from?

Thank you for your help.

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What is the condition of the inside of the tank?  Is this tar from some sort of tank sealer that someone put in the tank?  A lot of crud rust sediment etc can accumulate in there.  Although not "proper" I had put an inline filter on the one I owned.  My tank was really good but I didn't want to remove and and was still getting some stuff out of it.

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The "tar" is old fuel that sat long enough to break down into varnish. Been happening since man invented gas/diesel. 

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2 hours ago, iowaboy1965 said:

The "tar" is old fuel that sat long enough to break down into varnish. Been happening since man invented gas/diesel. 

Or the dissolved rubber from the inside of fuel lines, which has been going on since they started mixing ethanol with gasoline.

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The inside of the tank is pretty much as expected. I get some fine crud in the sediment bowl, but nothing large or restricting.

The tank has not been sealed, so that's out.

The strange part is mine is gas and the one on you tube was a diesel, both had the same tar in it. That was the part that seemed strange. When I say tar, it looks exactly like roofing tar, jet black and thick.

There are no rubber lines, everything is hard plumbed, unless the inside of the hard lines is coated with something.

I have taken the carb off and tore it apart. Some real fine rusty colored dust in the bottom of the bowl, but that's all I can find. No ethanol crystals or anything else.

As mentioned, the tractor had been setting for a dozen years or so. The people I bought it from, had the carb rebuilt by someone when they were trying to get it started. It was running very rich when I got it, so I pulled carb to check it out. One thing I found was that the main jet on the end of the "anti diesel" solenoid was missing. Got a jet and put it on, helped, but still rich. I was wondering if there was something else missing that I had missed. I checked the intake butterfly, looks good. I did notice that there is a tapped c'bored hole in the bottom of the bowl that does not have anything in it. The passage just leads down into where the solenoid goes in, so if it gets too much gas, it is regulated by the main jet, so I don't see that being an issue. The other thing is, the idle mixture screw, if I run it clear in, it still runs, and running it in and out does not seem to change anything. I put some ink marker on the end of the needle and screwed it clear in, and it seems to be seating alright.


The middle hole in the bottom of the  bowl is the one I was wondering if something is missing here. The (2) side holes also feed into the same area.
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I don't see anything that seems to go in there.

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I was hoping to get some hours on the tractor first before I tried going thru everything to adjust and set it, but I need to get this quirk figured out first. I have not set any of the linkage on the governor yet, I can't imagine that would cause it to shut down.

Any more thoughts or ideas would be greatly appreciated.

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The bottom hole is just your bowl drain---plug #28 is all that s'posed to go in there.

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Yea, #28 is a separate plug, which is in place, and #33 is also there. There obviously isn't much to them, but they can sure cause you grief.

The tractor only has 1,000 hr's on it, so the cross shafts and bushings are good and tight. All of the passages blow thru good.

That seat that the venturi sets on, #30 I assume that the seat is just a snug fit into a straight bore, or is there a ledge in there that it is setting on? If I set the venturi in there with the gasket in place, the venturi seems to be able to move around some. Should that be captured in there tight or doesn't it really need to? I didn't want to try to tap on it to see, until my gasket kit comes to see if there was a new one, before I manage to break it.

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i was pondering this same question the other day, i have an old metal boat tank i would love to soak and get the gunk out of in there. its pretty gooey

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