I have an MM Model X-450a which I understand to be a licensed copy of the OHG X-450 mixer. They are very simple and easy to disassemble / reassemble, so long as you keep in mind that you are working on something which is no longer manufactured and parts will be hard to come by.
The below is made of quotes from this forum and pics, both my own and those found on the web. Thank you to all that have contributed to this forum over the years, it is a great resource.
Fittings:
Above and to the right of the idle screw is a 1/4" port which connects to the enrichment valve. This typically connects to a manifold vacuum source (a PCV valve is a common location).
Below and to the left of the idle screw may connect to the idle mixture solenoid if used, or to a vacuum lock off, again if used, or just plugged if not.
The black hex plug above and to the left of the idle screw connects to the vaporizer vent with a 3/8" vacuum hose.
This is all there is on the X-450.
Franz
Idle Mixture Screw:
In = Leaner, Out = Richer
Metering Rods:
Shorter rods = richer, longer rods = leaner
There are only two metering rods for the 450, one for CNG, the other for LPG.
As for the metering rod height, you measure the stud height from the edge of the air-valve. It should be around .830-.835" for an open loop non computer controlled fuel mixture.
Split O-Ring:
Power Valve:The o-ring can be rock hard but as long as the air valve moves smoothly, it can be left intact.
The power valve should open when vacuum is lower than 5". If it is opening at values higher than 5" (i.e. 6"-20") the power valve spring has either lost its tension or it has been cut to change its operating settings (which to me is a bit of a no-no).
The original springs were 16mm (or 5/8" in imperial) long so my suggestion would be to check it and even just get a new one.
My understanding is the correct hose to connect it to is the PCV hose via a T fitting so I would leave that as it is.
Thanks for the plug, Storm. The piston serves two purposes, the one you mentioned, where it allows extra fuel, plus it closes the vent to the top cover, allowing the air valve to raise, decreasing air restriction. By the air valve lifting, the metering pins also raise, allowing additional fuel, somewhat proportional to the amount of airflow. At low airflow speeds, the mixer uses the air valve to increase air velocity across the metered openings in the body. When the air valve raises, the mixer behaves more like a venturi. Its complicated and very efficient. Just make sure the metering pins move freely and the air valve moves without binding. You can loosen the three screws and gently move the top cover around until the valve doesnt bind.
Franz
Just in case you're not aware of it, the X-450 will not run properly unless the power valve is Teed into the vacuum line between the PCV valve and manifold vacuum. The PCV acts as a regulator to prevent the valve from fluttering as it will if connected directly to manifold vacuum. The bottom of the power valve also delivers LPG down the vacuum line when the valve closes, so if it flutters the mixture varies wildly until the engine stalls.
Impco VFF30 Lockoff
Some external links I have found useful:what is the harm in connecting the lockoff to full manifold vacuum?
The VFF30 needs very little vacuum to operate, so manifold vaccum over-stresses the components inside the lockoff. Over the years working in the industry, however, we did see many vehicles hooked up that way, and operating just fine.
http://www.traycana.com/catalogues/stre ... alogue.pdf
http://www.jeephead.com/myjeep/propane.htm
https://www.pirate4x4.com/forum/general ... ing-4.html