The spring and plastic part should be removed, leaving only metal parts on the main body and the top cover. I used carburetor cleaner to remove all the grime, followed by acetone, but any good solvent should work.

Once most of the dirt was removed, I lightly sanded the inside of the primary chamber with 400 and then 600 sandpaper, followed by a 1500 grit automotive rubbing compound. A final rinse with acetone made the parts squeaky clean.

The plastic parts shouldn't be put in the solvent, but they need to be clean none-the-less. I used regular soap and water for this job.
There is an air-filter on the intake....
....and a plastic rocker, both of which should be removed and set aside.
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