Leaking decomp valve - replace vs. plug?


I trying to get a Derbi Start V to fire, unfortunately I am having low compression (~75 PSI). There is a minor leaking at the head gasket and major leak at the decompression valve. I am using a brand new head and an old decompression set-up.

I lapped the head and decompression valve with no improvement. I switched the decompression set-up to another head with the same results. Should I plug the hole or get a new set-up from treats?

I am going to mate the cylinder/head surface.

Re: Leaking decomp valve - replace vs. plug?

Or should I try a copper head gasket?

Re: Leaking decomp valve - replace vs. plug?

or buy a decompless head

Re: Leaking decomp valve - replace vs. plug?

If you can replace the decompression valve without spending a fortune, do so. Otherwise see if you can disassemble the existing valve and grind it back to health with valve-grinding compound, available at the oldest auto parts store you can find. Ask the oldest guy there how to use it, too.

The valve may very well not be the problem, however: the head gasket is far more serious, for I think you can really gouge out the head or barrel with the hot combustion gases. Assuming that your surfaces and gasket are in good shape, see if you can find the torque specifications for your head bolts and the others (intake and exhaust bolts, and running gear like wheels) as well. Purchase a torque wrench from Harbor Freight Tools: they're inexpensive and indispensable for this work. Then torque your head to proper specifications and your leak should disappear.

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