Sunday, June 5, 2011

Weed Eater FeatherLite SST Fuel Tank Repair/Replacement

A Note re Tubing and an Update -- TUESDAY, APRIL 29, 2014

I didn't try to obtain proper fuel line tubing for this; I just used stuff that I had on hand. The black tubing pictured further down didn't work out -- it wouldn't take immersion in fuel. It swelled up and came off its nipples.

I replaced the black tubing with intravenous (IV) supply tubing, and that has worked remarkably well. It still stiffens and needs to be replaced periodically, but it holds up better than the original stuff did. I imagine that any small engines repair outfit could supply the 'correct' tubing, if you have nothing suitable on hand.

All in all, my repair method shown here has proven to be sound, and I've applied the same method to the short 'primer overflow' tube as well. The trimmer is still operational after nearly three years.

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I've also had occasion just recently to do some repair work on the Zama carburetor -- it needed new diaphragms.

A carburetor removal procedure is here.

Diaphragm replacement is shown here.

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When I went to start up the trimmer for the first time this season, it was no go, no way. A little investigation revealed that the fuel supply tube in the fuel tank had turned into something with the flexibility of uncooked pasta. The fuel pickup/filter had broken off entirely. I fished it out of the tank and here's what I had.

Before I go to a parts dealer and hand over a wad of after-tax dollars for a new fuel tank, I'll look into repairing this.

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First thing is to disconnect the two tubes at the carburetor -- they just slip off their nipples.

The tank is attached to the engine's outermost cowl piece. That cowl/tank assembly is fastened in place by five screws. (That cowl piece is also the end-cap for the engine's crankcase. Once that's off the crankcase is wide open, so you want to take care about cleanliness.)

The screws involved are all washerhead types with T25 Torx recesses. The four that go into the crankcase are 10-24 x 3/4" thread-rolling screws. The one screw at the top of the cowl is a No. 10 x 5/8" thread-forming screw.

The fuel tank is fastened to the cowl piece with two No.10 x 7/8" thread-forming screws w/flange washers.

And that's all it takes to get to where you could replace the fuel tank if you needed to. The only 'complication' is that, as I mentioned earlier, you've unavoidably opened up the engine's crankcase. With the cowl piece removed, here's how the engine looks.

Needless to say, you don't want any grit to get in there. At reassembly, I'll apply some RTV gasket maker to the face of that gasket. A crankcase leak in a two-stroke engine is fatal to engine operation.

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The cowl piece and fuel tank were just filthy with sticky, tenacious two-stroke muck, so I gave them a good scrubbing in the parts washer.

Here's a shot of the business end of the cleaned up fuel tank. (It's not a very good photograph. Digital cameras seem to have trouble with certain types of rounded surfaces up close. I've noticed the effect before.)

That tube that's still left on the tank is the primer's 'overflow' tube. It's condition is marginal, but it's still serviceable.

I tore away the old supply tube remnant entirely. It appears that what the factory does is they simply pull the new tube through a tight-fitting hole. The tube's resilience seals it in the hole.

I don't have identical tubing to use for a replacement, but I do have some tubing on hand that fits the carburettor's input nipple and looks more-or-less suitable. Its outside diameter is just shy of 1/4" -- considerably larger than the original tubing. If I can come up with a double-ended nipple that I can install in the wall of the tank, I can make it work. This should be interesting.

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And here's my double-ended nipple.

It's a piece of 5/16"-18 threaded rod bored through to accept a length of 1/8" diameter brass tubing. I soldered it together. Note the wrenching flats. They'll take a 7/32" wrench come installation time. Here's how I secured the threaded rod in the vise while I filed the wrenching flats. It's a good way to clamp any threaded piece of work with no jaw mark damage to the threads.

Saw through a hex nut and you get a rudimentary 'collet' in which to hold the threaded rod without marring it.

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Next up is to drill and thread the fuel tank to accept the new nipple, then install the nipple and replacement fuel supply tube.

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Here are the nipple and supply tube in place. I just have to attach the filter and tuck the tube/filter inside.

I used a 1/4" drill for a tap drill. 1/4" is 0.007" smaller in diameter than the letter size 'F' drill you're supposed to use for a 5/16"-18 tap. My thinking there was to try to get a better than 75 percent thread cut in the relatively soft tank wall.

I've used CA adhesive on the nipple's threads. I'll reassemble everything, give the crankcase gasket's sealant some time to cure and try it out with freshly mixed fuel.

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Here it is all back together.

And I got it running after a bit of an ordeal with the carburettor. At first it simply would not start. I took the carburettor off, dismantled it somewhat and flushed and blew out its passages. 'Put it back together and it still wouldn't start. 'Took the primer bulb and body completely apart, blew out its passages, put it back together and it started and ran fine. Something in that mystifying little device must have been plugged. I suspect that the embrittled, broken tubing must have shed some particles that got drawn in while trying to start the engine.

Anyway, my fuel supply tube repair looks good so far. I don't know for certain whether the tubing I had on hand to use is fit for continual immersion in gasoline. I imagine I'll find that out soon enough. As far as I know, CA adhesive has very good solvent resistance, so the nipple's installation should be sound. I think I can safely say here that making and installing a double-ended nipple is a good way to repair one of these fuel tanks.

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