Leaky Gas Cap

bul_racer

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After the bike was sitting for many years I found the original gas cap gasket was disintegrating so I bought a new one from Mike's. I still haven't gotten the bike running but just from opening & closing the cap for de-rusting it began to come apart. Left pic. I found a replacement gas cap on ebay that was supposed to fit my bike ('80 xs650SG) but it didn't. Thought maybe I could just use the gasket but that didn't work either. Pic 2. Then I ordered a gasket from XS650Direct. Pic 3. It fits and closes but leaks. I found a washer of the right size to fit inside the part that holds the gasket. I drilled holes in the washer to match the holes in the spacer. The idea being to add just a little more space, moving the gasket a tad farther from the base of the cap to make a tighter seal. This slowed the leak and I don't know but that it might be OK for normal use but when I turned the tank upside down there was still leakage. Not nearly as much as before but still leaking.

All this to avoid paying $40 to partzilla for what they claim is an OEM part. Sure, maybe it is but isn't it likely to have hardened over time? Also, I'm somewhat concerned that the whole setup seems to put a lot of pressure on the gasket. Why else did the one from Mike's fail? Why wouldn't an OEM part do the same?

Say I bite the bullet and get the part from Partzilla. What do I get since the gasket is shown as unavailable for my 1980 model. For 1981 the diagram shows part #2MO-25641-00-00. Will that work & should I buy it? I sure wouldn't want to spend the $40 after all this and have it still leak.

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DogBunny

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Gas caps are vented. Air has to get in as the gas goes out. Venting is accomplished by small offset holes in the assembly. So, of course, gas will leak out if you hold the tank upside down (or if the bike goes down). Or, sometimes, as the gas sloshes around if the tank is filled all the way up to the brim.
 

bul_racer

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Gas caps are vented. Air has to get in as the gas goes out. Venting is accomplished by small offset holes in the assembly. So, of course, gas will leak out if you hold the tank upside down (or if the bike goes down). Or, sometimes, as the gas sloshes around if the tank is filled all the way up to the brim.

Hi Dog,

Yes, of course this makes sense. However, in order to de-rust the upper portion of the tank it must be turned upside down so that the solvent can attack the rust there. Before my original gasket went bad I was able to invert the tank with no loss of fluid. Now, since the tank has been empty for some time I need to de-rust again but can't because the solvent won't stay in the tank when it is upside down. I suppose I could try removing the cap and sealing the tank main opening with Gorilla tape or some other means just to get the de-rust process done and maybe the gasket I have will be good enough for general riding.
 

DogBunny

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One: The tank does not need to be spotless. A little rust in the very top (or anywhere, really) won't hurt a thing.
Two: You can level the filler neck, and then fill the tank to the brim with whatever you're using. I used to do this all the time when I used mild acids.
Three: If it didn't leak before when you turned the tank upside down, then you had a cap that wasn't venting, and you would have stalled out down the road due to fuel starvation once you got running.
Four: It is very easy to fabricate a neck blank-off. Big washer on the outside with gasket cut from old inner tube. Washer on the inside with two sides trimmed so that you can angle it into the neck opening. Long bolt and some nuts so that you can tighten it.
 

bul_racer

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Thanks Dog! Good Info.
I didn't stall when I had it running but I wasn't able to get above 3K. I suppose that could be the reason.
I think I'm gonna take Door #2 for the rust issue.

Cheers!.
 

DogBunny

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If the tank has good paint, you need to be careful about not over-filling and spills. Reactions can and will take place, and the solution might expand -- this has happened to me -- maybe the solution gets warmer? You also need a strategy for emptying the tank when you're through.
 

bul_racer

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Update. DogBunny. From your suggestion about washers & inner tube scraps I got the idea to try a rubber freeze plug. Found a 1.5 inch plug in my tool box and it fit. When I tightened it down it was snug & so far hasn't leaked. I will leave it inverted overnight. I'll take a quick look to see if there are any other areas that need further treatment.

Anyway, looks like problem is solved. At least until I fill 'er up with gas and find out whether the gasket seal holds.
 

bul_racer

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Not concerned about the paint.

Strategy for emptying is to drain as much as I can of the solvent, then add some gas mixed with some oil to prevent flash rust. Open to better ideas if you have.
 

DogBunny

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