[Top] [All Lists]

carb oil

Subject: carb oil
From: Mike Duvall <>
Date: Fri, 28 May 2004 01:28:50 -0500
I too have tried a variety of oils in my carbs.  My Haynes SU workshop 
manual says to "top up the piston damper with thin engine oil grade SAE 
20w/50 until the level is .5 in above the top of the hollow piston rod. 
  On dust -proofed carburettors, identified by no vent hole in the 
damper cap, the oil level should be .5 inch below the top of the hollow 
piston rod."  I think all B equipped SUs are dust proofed.

I just fill the piston rod to the top and when I stick the damper in, 
it overflows and is amazingly about .5 inches from the top!  I also 
have been using pneumatic tool oil.  It has additives to keep the tools 
clean so I figure the slight overflow might help keep the piston moving 
freely up and down in the suction chamber.

The way I read how the SU  carb operates ( I imagine the Zenith is the 
same) , the thinner the oil, the richer the mixture will be upon 
acceleration.  Just guessing, I would say that Marvel Mystery oil is 
the thinest followed by ATF and pneumatic tool oil.  I think ATF is 
about 7.5 to 35 weight.  The newer 5w/30 engine oils might work very 

I'm always running into people who say the used to own an MG but they 
could never get it to run right. I had one guy tell me he adjusted and 
adjusted the carbs and never could get them right. The manual says not 
to fiddle with the carbs. My guess is people would never put oil in 
their carbs.....any oil is better than none at all!

50 MGTD, 59 MGA, 65 MGB 

<Prev in Thread] Current Thread [Next in Thread>