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Rusty Tank 1978 KZ750 Twin 02 Jan 2023 07:21 #878436

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Hi everyone:

Im new to this forum and hope this is the place to post this. My uncle gave me a 1978 KZ750 Twin with 8,000 miles on it. The paint and body are rust free and it looks great. BUT when I looked in the tank I noticed rust. I tried to post a photo but keep getting a message that says "you do not have permission to view this page."

The bike has sat in a garage for a long time. The rust seems surface because when I stuck my finger in an brushed it, it fell right off into the fuel. It was like liquid.  What is the best way to fix this and how long before it gets bad? I dont have a lot of money and dont want the hassle of trying to find a new tank before its too late.

Danny

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Rusty Tank 1978 KZ750 Twin 02 Jan 2023 07:30 #878437

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Vinegar worked well for me on two tanks, the worst one was in really bad shape and turned out great. 


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Rusty Tank 1978 KZ750 Twin 02 Jan 2023 07:30 #878438

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Hi everyone:

Im new to this forum and hope this is the place to post this. My uncle gave me a 1978 KZ750 Twin with 8,000 miles on it. The paint and body are rust free and it looks great. BUT when I looked in the tank I noticed rust. I tried to post a photo but keep getting a message that says "you do not have permission to view this page."

The bike has sat in a garage for a long time. The rust seems surface because when I stuck my finger in an brushed it, it fell right off into the fuel. It was like liquid.  What is the best way to fix this and how long before it gets bad? I dont have a lot of money and dont want the hassle of trying to find a new tank before its too late.

Danny

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Stop using your back button to select your picture.
AND check out this article. www.kzrider.com/articles/technical-tips/22-rusty-tanks
Bill
www.KZ1300.com
Riders:
1968 BSA 441 Shooting Star, 1970 BSA 650 Lightning, 1974 W3, 1976 KZ900, 1979 KZ750 Twin, 1979 KZ750 Twin Trike, 1981 KZ1300, 1982 KZ1100 Spectre, 1987 Yamaha Trailway, 2000 Valkyrie, 2009 Yamaha Roadliner S. 1983 GL 1100
Projects:
1947 Indian Chief, 1985 ZN1300

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Rusty Tank 1978 KZ750 Twin 02 Jan 2023 07:32 #878439

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Hmmm. I just added the pic and it wont let me .

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Rusty Tank 1978 KZ750 Twin 02 Jan 2023 07:32 #878440

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but how do you stop it from flash rusting?

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Rusty Tank 1978 KZ750 Twin 02 Jan 2023 07:39 #878441

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After rinsing out the vinegar,( I used a garden hose) mix a box of baking soda with warm/hot water and shake well then rinse well with clean water. 
When it dries I sprayed fogging oil in the tank to prevent rust.

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Rusty Tank 1978 KZ750 Twin 02 Jan 2023 07:40 #878442

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Welcome aboard. The solution depends on how bad things are at the bottom of the tank. That is where water and dirt and chunks of rust will settle.

First, drain the tank and carefully dispose of the old, rotten fuel. Do not try to reuse it.
Then remove the petcock (it will need rebuilding or replacement) and make a metal plate to block off the hole. You can use a piece of an old inner tube or something similar as a temporary seal. 
If the rust is not too bad, fill the tank with white vinegar. Put the cap back on and shake the tank vigorously.
Let the tank sit with the vinegar in it overnight. 
The next morning, shake it some more.
Repeat this for two or three days.

Carefully drain the old vinegar, paying close attention to what comes out. If it is just mildly discolored, repeat the process again with clean vinegar.
If the vinegar is really dark, or there is noticeable sludge or chunks, a more aggressive approach may be needed.

While this is going on would be a good time to rebuild the petcock, and prepare for rebuilding the carbs. They will need it.

Once all the parts of the fuel system are clean, reinstall them with some new fuel lines and put some fresh fuel in the tank, then adjust the carbs.

 
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1981 KZ1000 LTD awaiting resurrection
2000 ZRX1100 not ridden enough
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Rusty Tank 1978 KZ750 Twin 02 Jan 2023 07:47 #878443

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Welcome aboard. The solution depends on how bad things are at the bottom of the tank. That is where water and dirt and chunks of rust will settle.

First, drain the tank and carefully dispose of the old, rotten fuel. Do not try to reuse it.
Then remove the petcock (it will need rebuilding or replacement) and make a metal plate to block off the hole. You can use a piece of an old inner tube or something similar as a temporary seal. 
If the rust is not too bad, fill the tank with white vinegar. Put the cap back on and shake the tank vigorously.
Let the tank sit with the vinegar in it overnight. 
The next morning, shake it some more.
Repeat this for two or three days.

Carefully drain the old vinegar, paying close attention to what comes out. If it is just mildly discolored, repeat the process again with clean vinegar.
If the vinegar is really dark, or there is noticeable sludge or chunks, a more aggressive approach may be needed.

While this is going on would be a good time to rebuild the petcock, and prepare for rebuilding the carbs. They will need it.

Once all the parts of the fuel system are clean, reinstall them with some new fuel lines and put some fresh fuel in the tank, then adjust the carbs.



 
Thanks. Here is what my uncle told me. 3 months ago he was going to get the bike running again. The tank was empty with only tiny spots of rust in it. He bought a pingle petcock and washed the tank out and put fuel in it, but it flash rusted. He put filters on the fuel lines and really was ready to go. The carbs were rebuilt from top to bottom with everything replaced with real parts, not aftermarket junk. But he bought a Honda CBX 1000 and lost interest.

So the rust in it is really the beginnings for rust, not pitted junky flaky stuff. He said he made the mistake of letting it flash rust, whatever all that is. Im still happy to have the bike, I just dont want it to rust. Will Drygas stop the rust? Something like HEET?

Thanks guys

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Rusty Tank 1978 KZ750 Twin 02 Jan 2023 07:59 #878445

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Heet is alcohol which will attract moisture, you could use WD40 or pour some 2-stroke gas mix in it.

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Rusty Tank 1978 KZ750 Twin 02 Jan 2023 08:03 #878446

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Darn! I put a half bottle of Heet in it. Oh well. I'll do the vinegar and WD40 thing then. Would any lingering WD40 mess up the fuel lines or carbs when it flows through the system?

Here is the bike

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Rusty Tank 1978 KZ750 Twin 02 Jan 2023 08:27 #878447

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I doubt WD 40 will harm anything in the fuel system after all it is petroleum based but I use fogging oil because that's what it's made for.

Nice looking bike ! If it's been sitting for awhile a good cleaning of the tank with vinegar should be done it might surprise you what comes out and save you from future problems.

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Rusty Tank 1978 KZ750 Twin 02 Jan 2023 08:44 #878448

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but how do you stop it from flash rusting?

 
Flash rust is not a problem if you follow my method in the article. You just rinse out the tank with water let it drain for a minute and then spray WD-40 into the wet tank. It'll take quite a bit of WD-40 but it'll penetrate through the water and coat the tank.
 
www.KZ1300.com
Riders:
1968 BSA 441 Shooting Star, 1970 BSA 650 Lightning, 1974 W3, 1976 KZ900, 1979 KZ750 Twin, 1979 KZ750 Twin Trike, 1981 KZ1300, 1982 KZ1100 Spectre, 1987 Yamaha Trailway, 2000 Valkyrie, 2009 Yamaha Roadliner S. 1983 GL 1100
Projects:
1947 Indian Chief, 1985 ZN1300
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