carb oil leak

[kully 560]

 I need a little help from the forum again, I have 1971 4 bolt su carbs that seems to have a small oil leakage from the mixture nut. not bad but when I adjust the mixture my fingers get wet with oil. is there a o-ring in there I can change? also can it be done with the carbs still in the manifold buy removing the assembly from the bottom of the carbs?  thanks 

[SteveJ]

Are you sure it's the carb oil? It's a tricky path for that oil to get to the bottom of the carburetor.

[kully 560]

hi Steve, I am not sure but when I do adjust the mixture nut there is a little oil on the adjusting nut. I do not know where else it could be coming from! my finger always has oil on it after the adjusting. now when I add oil to the carb, I fill it to the inside the ring lip that can be seen when the filler is open down below, I would guess about 1" down.

[Mark Maras]

 How often do you have to add oil to the carbs?

[kully 560]

hi Mark, I do not drive the car much, maybe 500 miles a year.  the oil level is always down below the lip ring in the filler neck. but it is never dry or out of oil. I always see oil down there.

[Mark Maras]

 With the engine off, lift both carb pistons to the top. There should be considerable resistance in both. Then let them drop. They should drop at close to the same speed and hit the carb bridge with an audible clunk.

[kully 560]

ok Mark, I will try that !

[kully 560]

ok Mark, I just check the piston lift, and they both have considerable resistance and drop pretty fast. but the rear seems a little faster than the front carb. I do have a slight clunk from both carbs as you said. but I did add a little oil to the carbs to bring up the oil level to the full mark early today and I never check the level before the oil top off. [my bad] I do know that if I over fill the carbs with oil the other excess oil gets burned off by the engine.

[Captain Obvious]

You are correct that overfilling the carbs with more oil than necessary won't really cause a problem. It'll just run down into the carb throat and be pulled into the engine when you start the motor. But 500 miles later, that should have happened already and should have burned off by then.

In other words... If you put oil in the carbs 500 miles ago, but the mixture nuts are wet today... I'm skeptical that it's oil from the carbs that is making the mixture nuts wet. I'm thinking that maybe it's partially evaporated gasoline mixed with a little blowback from the intake manifold mixed with a little road dust?

There was a thread many moons ago where we talking about oil leaking out of the damper tubes. Seemed improbable, but possible, with the flat top carbs, but seemed impossible with the round tops? I can't dig it up right now, but maybe someone can find that old thread?

[Mark Maras]

 I don't know where the oil is coming from but like C.O. I don't think it's coming from the carb reservoir. Ztherapy has an excellent video on SU carbs. It describes their function in detail and has many tests to ensure the carbs are working properly. With that thought in mind, you might give Steve at Ztherapy a call and ask him about the oil problem.

[kully 560]

thanks for all the help from this great forum.

[kully 560]

solved, as suggested by Mark I did call Steve over at z therapy today about the leak problem. now if you happen to over fill the carbs with oil and put the piston plunger back in, it will spill over in the dome and come out the bottom when the piston is inserted. I