Petrol in the Sump Oil

[Otahuhu]

I recently replaced at the same height to a dual 1 1/4 updraft carburetor a larger capacity Stewart vacuum tank The tank  has a shut off tap that is turn off when car is in the garage When the car is stationary with the tank valve open there is no petrol leaking out the carburetor overflow pipe I replaced the oil in the sump with new just below the fill line After a short run have found that petrol has leaked into the sump oil I used the same 5/16 dia pipe from the vacuum tank to the carb Would  the larger vacuum tank capacity deliver to much fuel ? The vacuum tank gets its vacuum from a vacuum pump Any thoughts why this occurs? Thanks    

[Rusty_OToole]

Where is the vacuum pump? If it is attached to the oil pump as some are that could be the source. With an updraft carburetor it is not coming from the carb unless it is ridiculously rich.

[Stude17]

 An issue that sometimes arises with Stewart Warner vacuum tanks is that the  needle operated by the tank float to cut the vacuum when the tank is full does not seat properly in the brass seat in the die cast tank lid.  Generally this is caused by the brass seat becoming loose and when this happens raw fuel is drawn along the vacuum line and into the intake manifold or in your case the vacuum pump and if it is operated by the oil pump into the sump oil.  I had this happen on my 1925 Overland causing dilution of the oil and flooding of the intake manifold. I would suggest that you check this brass seat carefully and if it is loose it will have to be repaired or the die cast lid replaced with one that is not loose. On mine I machined a new brass seat and replaced it but this is a lot of work.  I have heard that if it is not too loose Loctite may do the trick.