I recently discovered that the vacuum stat on the oil bath cleaner would start leaking at very high temperatures, leading to extremely hot air being fed into the carburettor if the engine bay air was already hot. I saw up to 55 degrees C going into the carburettor, with the engine bay at 45C .. While I try to source a more reliable vacuum stat, I came up with a temporary electrical alternative. I bought an EGR solenoid valve - might as well be one for a VW or Skoda... https://www.ebay.co.uk/itm/224995954344 And a thermostat: a KSD9700 type 30 degrees C normally closed (makes connection at low temperature) thermostat. https://www.ebay.co.uk/itm/274479686067?var=574636771797 The vacuum pickup from the carburettor or manifold goes to the top nipple on the valve, the flap actuator is connected to the nipple nearer the connector. This means that when the solenoid is off, the flap actuator is open to air through the cap clipped on the bottom of the solenoid. The thermostat is placed somewhere between the top of the air cleaner and the input to the carburettor in the intake air flow, to measure the same air the stock vacuum stat measures. A fused ignition feed is connected via the thermostat , and then the output of the thermostat is connected to the solenoid, the other connector of the solenoid is grounded. In operation , this circuit pulls in the solenoid, and connects vacuum to the flap until the air leaving the air cleaner reaches 30 degrees C. According to the thermostat datasheet, the thermostat then opens until the air coming through reaches 20 degrees C. In fact what happens is that the engine bay warms up above 30C and the thermostat never closes until the bus cools down at the end of the journey.
