Damper Oil

[checker]

I'm needing to put oil in my SU carb dashpots.  I know they make a specific SU Damper oil but I doubt if it's as special as its price reflects.  What do any of you use for oil in your dashpots.  Thanks

[Bloo]

I used to make my own mix out of multiviscosity motor oil and ATF. There may have been a little Marvel Mystery oil in the mix at times, too. I would mix it until it did what I wanted, and just hope it would be ok in the winter too. Usually it was. I know that isn't much help, but I can't really describe it.

 

The basic thing is that air is lighter and moves faster than gas, so the dashpot needs to hold the slide back until the gas can get moving. I liked to run a bit leaner than most British car fans would recommend (I like clean spark plugs), so I probably had the oil thick enough to have the mixture go a bit richer for the moment when the slide opens, and assure that it wouldn't go lean and hesitate or spit back. If you overdo it though, and get the oil too thick, the slides will lag too much.

 

It is probably a good thing that the oil gets thicker in the cold weather, making the transitions richer on days the gas wont vaporize well, but if too thick the oil might sort of "freeze up" on some 10F day and become so thick that the carburetors won't work right at all.

 

Have fun!

 

 

 

 

[checker]

21 hours ago, Bloo said:

I used to make my own mix out of multiviscosity motor oil and ATF. There may have been a little Marvel Mystery oil in the mix at times, too. I would mix it until it did what I wanted, and just hope it would be ok in the winter too. Usually it was. I know that isn't much help, but I can't really describe it.

 

The basic thing is that air is lighter and moves faster than gas, so the dashpot needs to hold the slide back until the gas can get moving. I liked to run a bit leaner than most British car fans would recommend (I like clean spark plugs), so I probably had the oil thick enough to have the mixture go a bit richer for the moment when the slide opens, and assure that it wouldn't go lean and hesitate or spit back. If you overdo it though, and get the oil too thick, the slides will lag too much.

 

It is probably a good thing that the oil gets thicker in the cold weather, making the transitions richer on days the gas wont vaporize well, but if too thick the oil might sort of "freeze up" on some 10F day and become so thick that the carburetors won't work right at all.

 

Have fun!

 

 

 

 

Thanks Bloo.    I filled it tonight with 3/4 transmission fluid and 1/4 0w-20 oil.  Some sites recommended 50/50 with oil and 3 in 1, others said 100% trans fluid.  Like you I comprised.  I was surprised at how little the fresh rebuilt carbs needed.