Wednesday, November 20, 2019

Carb Cover Pin Mystery

 So yesterday I found myself at work diagnosing a string trimmer with running issues. That in itself isn't unusual at all, it just seemed odd running a strimmer outside in the cold with snow on the ground. I determined the unit was starving for fuel which isn't unusual either due to the fact that many of my repairs are fuel related and most fuel related repairs involve lean running conditions, or a lack of fuel. The usual suspects range from a stiff metering diaphragm to a cracked fuel line or plugged fuel filter. Maybe even lack of fuel because its being displaced by water. Usually I can guess at the problem before actually finding the problem but this time just seemed different. I have a routine that I follow and the first step is to dump the fuel and investigate. The fuel I dumped out was clean enough and smelled fresh enough to trust it in the space shuttle, if it were a two stroke. For you gearheads, lets just take a moment to imagine the sweet sounds of a two stroke engine big enough to move the space shuttle. BRAAAAAAAAAAP! RING-A-DING!
 Ok, I'm back.
 I removed the fuel filter and it looked good too. Next I connect a Mity Vac where the filter was and pressurize the fuel system. It should hold 10 psi but I was having a problem. The carb wasn't holding pressure. Once removed from the engine, this is what I saw:

 For the non-gearheads I'll give you a hint. That cover is on crooked. In fact its crookeder than a second term politician.  I've seen rifle sights at the county fair shooting gallery that were less crooked. In fact, I'll bet it was something like this that inspired Chubby Checker to write that song about the Twist.

 The red arrows point to where alignment pins used to be. They are part of the casting and how or why they broke is a mystery. The screw that holds the cover on was tight and I have to wonder if it was assembled wrong at the factory. This trimmer was traded in and I think the reason was because it always ran like number 2. See, this cover seals the fuel pump diaphragm and this would explain the lack of fuel getting to the engine. No problem, I have a big bucket of carbs I can dig through and find a new cover. The new pump diaphragm will come in a rebuild kit.

 The lone cover in front of a pile of carbs. Surely I'll have a donor in here.

 No such luck. This carb isn't a common Walbro or Zama, its some other cheap brand with a name I can't pronounce without straining a tongue muscle. Like a lot of things from over seas, these are duplicates of name brand parts just built cheaper. The difference here is that they build these 180 degrees off. Oh they work the same but everything is flipped end for end or inside out or kittywampus. That means a zama cover won't work even though its the "same" carb. My big bucket of carbs has let me down and the entire carb is too expensive to justify the repair so I'll just order the cover. The boat carrying that new cover should arrive on our shores by the time the snow melts, just in time for strimmer season.


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