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Stromberg AAUV8 1951


Pete O
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Anybody have experience rebuilding a Stromberg AAUV8?   I have it apart, and am following the shop manual for disassembly and descriptions of how the internals work.  My question is about the power piston.   Per the manual, in normal operation, it is held open by the manifold vacuum working against the spring tension.  When at high speed or open throttle, vacuum drops and the spring extends the piston, opening a jet to deliver extra fuel.   The piston looks like a nail with a spring around the shaft, and it's attached to a brass base with a washer against the spring that seats into the air horn.  I removed the piston, and cleaned out the well and vacuum passage below (above when right side up) where the brass base seats .    But I don't see how vacuum from that passage can do anything to retract that piston.  The brass base is sealed.  I was expecting maybe a passage where I drew the arrow in the picture which would admit the vacuum to draw the piston up.  But instead, it's a small brass cap.  If you remove the cap, the shaft of the "nail" is simply peened over to keep it from sliding out of the brass body.  

 

The brass base is an interference fit in the well in the air horn.  The only way it seems to me that this can work is if the brass base would be a slip fit, and the whole brass base would retract with the vacuum.   Is that right?  I might have to make double sure that I have all the gunk cleaned out of the well in the air horn, and/or polish that brass base to allow a slip fit.

 

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Well I think I answered my own question.  I went ahead and polished the brass base and used a gun barrel brush on the well in the airhorn to clean it completely, and now that brass base slides in the well.  Applying a vacuum to the port in the airhorn that leads to the well now draws the piston up as it should.

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