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JFairman JFairman is offline
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Join Date: Jul 2006
Location: S. Florida
Posts: 7,267
The hose connection on top of the WUR going to atmosphere is a vent line that should go to the air cleaner housing or into the top of an aftermarket air filter on top of the air flow meter if thats what you're using.

If a hole wears into the steel fuel metering disc in the top of the WUR then control pressure fuel will fill the control pressure housing and leak out that vent and could lead to a gas fire if it goes anywhere else other than back into the air intake.
Don't plug it either because the control pressure regulator housing has to be able breathe as the synthetic boost pressure diaphram in the bottom of the WUR fills with air pressure under boost and moves downward and upward and displaces some air inside the WUR housing as it moves.

My theory on the rough hot start running is a lean condition caused by the bimetallic spring inside the WUR heatsoaking in the hot engine compartment after parking around 30 minutes - after driving it for at least 30 minutes on a hot summer day so everyting is hot.
This won't happen on a cold winter day. Instead you'll get a high idle from the cold start auxilliary air regulator that is also controlled by a mechanical bimetallic spring with 12 volt heater element bypasing air around the closed throttle body butterfly that cooled off alot faster than the cylinder heads after parking for around 30 minutes - after driving it fully warmed up.

When the fuel pumps and motor are running relatively cool fuel is constantly flowing through the top section of the mechanical WUR/control pressure regulator and returning to the gas tank. That keeps engine heat transfer from heat soaking it hotter than the 12 volt heater element on the bimetallic spring inside the WUR gets when the motor is running.

If the temperature of the WUR gets higher than normal running operating temperature it will raise control pressure higher than it should be and lean out the motor. That lean condition can be up around 15-16:1 and is most noticeable by low stumbling rough running at idle speed

Once the motor is started again and runs for a little while the cooler fuel constantly flowing through the WUR and returning to the tank gradually cools it back down to normal operating temeratures and the control pressure and AFR's lower back to where they should be and the motor runs smooth again.

Originally Posted by JWLindsey View Post
Great leads. There is one puzzling hose leading to atmosphere so I may plug that and see what happens. I have a 930 shop manual but I have been reading it too late at night to make any sense of it.

Many thanks for all the help.

Old 10-11-2011, 07:39 AM
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