I have just developed an air leak at front bulkhead behind gen set access door (see picture and my finger pointing at air diaphram port that is leaking air) this is constant when engine is running and shuts off a few minutes after shut down. Any ideas on fix and what does this control?

Hi bob, That is the venturi vacuum generator probably for your HVAC controls in the dash. As long as the vacuum doesn't have a leak, it should just cycle briefly while maintain the vacuum supply for use. However, if there is a vacuum leak, it will run constantly.

I would first check the vacuum lines for leaks, there should be a small reservoir close by, and you could pinch off the tube to it to see if the air out of the venturi stops and does not start. Make sure it is the tube going to the vacuum reservoir otherwise if youu have the air supply line to the venturi, it will blow off.

If the there is a vacuum leak or the venturi unit is bad, it will take the air supply to about 50 PSI before the regulator shuts it off.

If the unit still leaks air with a known good vacuum line, then it is the venturi that has gone bad. I had both of mine give up and I installed a motor driven vacuum pump.