Technical Cleaning Out Fuel Tank Suggestions

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Technical Cleaning Out Fuel Tank Suggestions

Lgabb

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I'm back on the '72 850 restore starting with the electrical and found the fuel gauge low fuel light not working. I had drained the tank a couple weeks earlier of the old fuel that had been in there for probably 20 years. Very stinky. When I removed the sending unit, I found it covered in a black crud, some hard and some soft. Shining a light in the tank, I found it in pretty much the same condition. I would like to clean this tank in place as it looks like I would have to remove the transaxle to remove the tank. Carburetor cleaner seems to dissolve this crud but it would take about $50 worth to get to the level of the crud in the tank. Someone on U-tube suggested toilet bowl cleaner but I'm not so sure of putting a corrosive in there. Does anyone have suggestions for cleaning out the tank in place?
 
Personally..

I would half fill with fresh fuel..

Thats basically the consituent ingredients of what has created this gunk
;)

It should soften it enough to make removal : flushing straightforward

You can strain the used fuel to catch the junk.. and reuse.


From my dirtbike days I know the US has massive variations of fuel quality and ingredients.

Dellorto carbs couldnt stand for more than a month in some states.
 
Thanks. I'll experiment soaking the old trashed sender first to see how well it will dissolve the gunk.
 
Hello , I have had to remove the tank from my 1974 850 only few weeks ago
In order to drop the tank u will have to remove the heater pipe there is two but u will get away with one then will have to remove the shock on rear left then remove the drive shaft , then remove the fuel filler cap pipe and there are two bolts holding on the tank it’s pretty straight forward job, remember to bleed the system after your finished as it will be air locked hope this helps
 
Hello , I have had to remove the tank from my 1974 850 only few weeks ago
In order to drop the tank u will have to remove the heater pipe there is two but u will get away with one then will have to remove the shock on rear left then remove the drive shaft , then remove the fuel filler cap pipe and there are two bolts holding on the tank it’s pretty straight forward job, remember to bleed the system after your finished as it will be air locked hope this helps
I would have to remove the transaxle to remove the tank on my '72 850 Spider. I put about 3 gallons of gas back in the tank and am letting it soak for a few days. It seems to be dissolving the black crud. I'll try running a brush around inside the tank and then drain the tank again.
 
I did that fuel tank removal/replacement job a few months ago and was thankful for the time the coronavirus quarantine allowed me to do it. It was a pain, but gave me the opportunity to check and replace shocks, most of the driveline parts, clutch parts, trans lube, hoses, cables, fuel gauge sending unit, etc. I'm now getting ready to do the same on a '67 which should be a little easier since it doesn't have the extra vent tubes of the later model.
Hopefully your tank was fairly full of gas during the years it was stored so that rust hasn't formed on the inside. It should be easier to clean out the gunk from old gas than rust, since the rust particles will cause an ongoing problem of carb jet clogging. Possibly consider two fuel filters inline.
I missed an opportunity to check out your project when I drove by your area on my way to the Indycar race in Birmingham a couple weeks ago.
 
I did that fuel tank removal/replacement job a few months ago and was thankful for the time the coronavirus quarantine allowed me to do it. It was a pain, but gave me the opportunity to check and replace shocks, most of the driveline parts, clutch parts, trans lube, hoses, cables, fuel gauge sending unit, etc. I'm now getting ready to do the same on a '67 which should be a little easier since it doesn't have the extra vent tubes of the later model.
Hopefully your tank was fairly full of gas during the years it was stored so that rust hasn't formed on the inside. It should be easier to clean out the gunk from old gas than rust, since the rust particles will cause an ongoing problem of carb jet clogging. Possibly consider two fuel filters inline.
I missed an opportunity to check out your project when I drove by your area on my way to the Indycar race in Birmingham a couple weeks ago.
When I took out the sender unit, there was just a little bit of surface rust around the hole so hopefully rust isn't an issue. I'll probably drain the tank this week and see how it looks inside. I'm about 35-40 minutes from I-65 so if you're down this way, you're welcome to drop by.
 
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If you determine that you need a replacement tank I have a couple of solid late model used tanks sitting around the shed. I now have only early model 850s so I don't any longer need spare late model tanks.
 
The tank on my '69 850 contained about 3 pints of rusty sediment which had (contaminated)* the entire fuel system, carb, etc. I removed the tank and pulled the sending unit. It was shot. Looking inside the tank I discovered a pair of baffles. The left side of the tank is accessible through the filler neck. The center through the sending unit. In order to access the right hand side of the tank I cut a 2 1/2 inch hole and attached a reinforcing flange. The Eastwood Co. sells a tank restoration kit. Basically, I spent the better part of a three day weekend washing the tank, etching it with acid, rinsing, etching, and coating the inside of the tank with a (looks like) vinyl liner. I don't know for sure what the liner chemistry is, but the local hot rodders like it on their cars. During the wash cycle I put old chains, nuts and bolts, and whatever else I could find that I thought would knock the rusty crud loose. I hung the tank from a tree and shook it for quite a while. Yes, the neighbors are sure that I'm nuts. I'm not sure I'd do it again if I could get my hands on a new tank. Keep it dry**, whatever you do! I found a new sending unit on-line for a reasonable price. I pressure tested the new flange at about 20 psi. No bubbles. Chickened out at higher pressure, didn't want to bulge the tank.
* Our friends have a much more descriptive word.
** No water in the fuel! Keep the tank full to prevent condensation.
 
Try a degreaser. I recommend something like Meguiars Degreaser, but you can use any commercial degreaser. Slosh it around inside the tank, let it sit and slosh again. If you seal the tanks (plug up the hoses and put a cup or something to plug the sender hole. Lay the tank on one of the sides and let the degreaser do the job - then turn the tank again. You need all six sides of the tank to lay flat. After you're done, dump out the degreaser and it should be clean. Inspect with a light.

There's also another product if you need to seal the tank (not rust holes, but rust in the tank). POR15 has a product to degrease, etch and coat the tank. I used a chain (real chain) and put it in the dry tank and shook the tank as I turned it. It knocked the rust off - it's a lot more work than you would think. Degrease, etch and coat - watch a Youtube video on the process.

Good luck!
 
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If you determine that you need a replacement tank I have a couple of solid late model used tanks sitting around the shed. I now have only early model 850s so I don't any longer need spare late model tanks.
I know this is an older thread, but do you still have any of those tanks?
 
Sea Foam. Works great, heavy mix with fuel, just a few gallons. Rock the 850 back forth, let sit for day or two, rock again, then drain. Rinse with soapy water, dry throughly for a few days. Repeat as needed. That’s about the best I have short of removing tank and taking to professional tank cleaner.
 
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