John Deere 820

Need sommeone to explain to me how this pony carburator system works. I can see that there is some sort of diapram with perhaps an adjustment screw. I can also see there is an electrical cut out switch of some sort perhaps linked to low oil pressure. An outline of how its all supposed to work would be great.
Thanks
Bill

What you are looking at there is the oil powered fuel shut off for the pony motor. When the pony has oil pressure it opens the shut off to supply gas to the pony carb. The sender tells you if the pony has oil pressure. Light off, pressure, light on no oil pressure. It also reminds you to shut off the pony ignition when the pony runs out of gas... Sometimes those diaphragms deteriorate and let gas into the oil. Deere still sells them (at least they did the last time I needed a set). The carb is a standard down draft style. I've rebuilt a couple and they're pretty simple.

that is an automatic fuel shut off, oil pressure from the engine pressurizes the cavity between the 2 diaphragms which pushes open a valve inside that lets gas through to the carb. so you really have a manual valve on an automatic valve which is how they came. the electric switch is the one for the idiot light to show if pony has oil pressure or not. the adjusting screw you refer to is not an adjusting screw, that is used to open the automatic valve and let gas through so if it runs out of gas or sets for a while and evaporates out you can fill up the carb by pressing in on that screw, the nut on the screw should be adjusted to just open the valve when pushed, don't want to push that screw in to much as that makes it more likely to tear the diaphragm and create a leak.

some guys including me put a different pressure switch with 3 terminals in there and then run our ignition wire to the distributor through it, that way you don't burn out your coils when the switch gets left on, when you do that you have to put a bypass switch on it so you send power to the distributor while cranking the pony as you wont create enough oil pressure to activate pressure switch until pony is running.

As Ive often said you guys are so helpful, two great explanation and much appreciated. Should have her running properly shortly. Waiting delivery of a water pump drive belt then Ill give it a try again.I think I also need to re~seal the maual gas shut off valve as its leaking.

Bill,

just an observation, but you have a good 'dip' in the fuel line. In my experience that causes problems.

The fuel tank has very little 'head' above the carb, any dip in the line allows air to get trapped.

You may have already discovered that keeping the fuel tank full makes life much easier, and prevents you having to blow into the tank to get the petrol flowing!