# Craftsman Trimmer



## jdlr (Jun 23, 2014)

Craftsman String Trimmer-358.798560 Walbro Carb (not sure of specific model).

This is a trimmer that I inherited and would like to keep running, but I am not sure of where to go next. I have read other posts about engines not starting, and I think I have covered all of my bases. The only two things I suspect are problems with the primer bulb and compression. To date I have: mixed fresh fuel, changed plug, verified spark, cleaned carb, replaced gaskets/flutter valve/diaphragm in carb, replaced fuel and vent lines. There is a small screen that does not come out, but it appears to be clean. The trimmer won't start, even if I spray starter fluid in the carb. 

I suspect a problem with the primer bulb because when I press it, I see fuel going into the carb, but a steady stream also flows back into the tank each time I press the bulb. As for compression, I have no idea how to measure this, other than what I have read here about pressing my thumb over the spark plug hole. I haven't done this yet. 

I also wonder about a thorough soaking of the carb to clean any varnish or sediment. Is there a solution to soak the whole unit in, or do I just spray the heck out of it? Thanks for your help.


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## usmcgrunt (Sep 16, 2007)

Hello and welcome to Hobby Talk jdlr. The operation of the primer bulb you describe is normal. The primer is actually a purge system that draws gas into the carb and returns it and any AIR in the system back to the tank. The carb is then ready to inject fuel when the engine pulses activate the fuel pump (diaphragm) in the carb. It does not squirt any gas into the carb throat as many four cycle engines do.

All two cycle engines require good compression and the ability to create vacuum in the crank case to run efficiently. You can remove the muffler and look at the piston and cylinder wall through the exhaust port. If you see and deep scratches on either, the compression is probably below an accepted minimum of 100 psi, and will cost more to repair on your unit than purchasing a new lower quality machine. A compression test should be the FIRST test performed on any two cycle before any other work is done. A lot of auto stores will let you borrow\rent a compression tester. I hope this information helps.


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## jdlr (Jun 23, 2014)

usmcgrunt,

First, based on your username, thank you for your service. Second, thank you for the advice. Not sure how this happened, but after I measured compression (105 psi) and double checked the presence of a spark, the darn thing started right up! Now I want to fine tune the mixture screw. Any suggestions as to how I should do this, other than just listening for it to sound right?


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## usmcgrunt (Sep 16, 2007)

Hello jdlr. Here are a couple of links to help with the adjustment.

http://www.zamacarb.com/images/techsupport/HowToAdjustCarb.pdf


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## jdlr (Jun 23, 2014)

Thank you again.


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