OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Victa Two Stroke Engines Victa Decompressor Valve - Rebuild How-To

Part 2 - Checking parts and Reassembly

Here's an exploded drawing, from Gregory's Victa Workshop Manual No. 103.

This is for the long type deco valve; the earliest models used a screw to retain the vacuum hose to the deco nozzle, as shown here.

The latest type of deco nozzle uses a barb to retain the hose, and has a brass restrictor.




Checking of parts, to assess suitability for further service, is chiefly concerned with the deco nozzle and poppet valve.

The nozzle must be a tight fit in the diaphragm cover, so as to avoid vacuum leaks.
Vacuum leaks can have the effects of the poppet valve not closing fully, and even leaning off of the fuel/air mixture, for really bad leaks.

The poppet valve must slide freely in its guide in the decompressor body.

It's also necessary to check that it seats properly, i.e. that the valve head is not bent.
This is easily done by smoking the valve face with a lighter or match, so that it has an even coat of soot. Or you could pinch some of the wife's lipstick, if you're game...

Insert the valve in the deco body, and use its stem to pull it against its seat, while spinning it around. When it's removed, it should show a bright ring where the soot has rubbed off, around the circumference of the face. If there's any break in that ring, the valve head is bent, and the valve must be replaced. It's NLA as a separate part, so it will be necessary to find a used one, or a complete valve assembly.

Bent valves are the reason for the brass restrictor fitted to the late black decompressor nozzles.

With the earlier unrestricted type, a 'carby side backfire' can slam the poppet valve head against a ledge in the cylinder head [which itself prevents the valve falling into the combustion chamber, if the valve stem fractures], and bend it.

Reassembly

What's in the repair kit:


The larger diaphragm fits this 'long' deco valve; the smaller fits the later 'short' type.

Reassembly is straightforward, with attention to the following points. Use steel wool to clean the mating flange surfaces, then commence assembly as per the workshop manual drawing above.

Ready to install the poppet valve retainer, with dividers for a spring compressor.


Ready to install the diaphragm cover.


Job done. Note that the diaphragm chamber clips are installed 'barbs up'; they are easier to tilt into place, if it's done this way. Just place the nozzle in position, but do not seat it fully, at this point. This is so that it can be 'timed', after the deco valve is screwed fully home in the cylinder head.