Symptoms of a rusty tank?

[Fyarl666]

81 GS400L,

Am I experiencing "Rusty Tank Syndrome"?

The bike was running tip-top when I put it away last fall. I have a new petcock diaphragm, the carbs were recently cleaned, airbox and filter are clean, and I have a new fuel filter.

I attempted to start it the other day. Fired up no problem, ran and idled just fine, but then it started struggling.

Now, the engine won't stay running at idle, I have to throttle it up to 3-4K rpm, anything else and it will just die.

UI suspect there's tank rust that's clogging the petcock screen enough to resrict the fuel-flow to my carburator. My plan is to remove and clean out the petcock, clean it and de-rust the fuel tank with a vinegar wash.

Any other suggestions? Anything else I may have missed?

 

[rphillips]

Would think if the screen will let enough fuel through to run at 3K or 4K, it surely is letting enough through to run at way less than 1/3 that speed.

 

[alke46]

Try removing the carb float bowls. When I had rust in my tank, it would show up in the float bowls and where do you think it went from there? Yep, right into the carburetor and would cause lots of trouble.
If you have rust in the the tank, removing the float bowls will let you see the small rust that is getting past the petcock screen.

 

[Cha5]

Pull the fuel pipe off & fill a CLEAN glass jar with fuel, at least half a pint, the flow rate will give you an idea if the petcock is blocked. Let this fuel settle for awhile then look at the bottom of the jar. If you can remove a float bowl then tank rust shows as red, if it's black then the fuel pipes are disintegrating.

If you have 'flakes' of rust then you need to refurb the tank, if it's just a powdery dust then you can fit an inline filter but don't bother with the tiny ones made for lawnmowers.