Good day to everyone!  Could  someone tell me what the two engine dampers do, ie...their function and I checked the oil in there and it is low.  What weight oil, 10W-20, would be the best?  Also, would you add while the engine is on?  Do not want to over fill and they are a little “funky”!

Thanks,  Tom

If you aren't sure what oil is in there now, you might as well just change it and the filter. If you have to move the car and want to ensure proper oil level then I'd go with 10W30. Then change it.

The most accurate way to check the oil is after the engine has reached normal operating temp, and has sat on level ground for at least 15 min.

 

Oil viscosity depends on your climate, and how worn and/or how much oil the engine consumes. 10W30 is pretty standard for an engine in good condition, and up to 20W50 can be used in engines that are more worn out.

 

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Thanks!!  Tom

Are you talking about the carbs oil? That's the dampeners I think of.

I use 20 weight in mine. A lot of people use automatic transmission fluid.

Yes, the carb oil.

Thanks, I really appreciate the help!!   Tom

 The dampers control air and fuel. At the bottom of the pistons, there are fuel metering needles. When the gas pedal is pushed the butterfly valves in the carb throats open. The incoming air lifts the pistons which allow more air and fuel into the engine. 20w oil is recommended by Nissan. I ran ATF in mine. The oil prevents the damper from lifting too fast. The delayed rise in the dampers temporarily speeds up the airflow and pulls a little extra fuel into the air stream. It functions as an accelerator pump. You really can't over-fill the carbs with oil. Any extra will be sucked into the airstream and burned by the engine. The primary fuel adjustment is in the float height. There are secondary mixture adjustments under the carbs that raise or lower the fuel nozzles.

Thanks Mark!!  What a really great explanation!   thanks for your time and expertise!!    Tom

Mark-Tom here again.  When I was looking at the fluid in the dampers, it was kind of pink/purple??  Would that be ATF?  did not look brownish like regular oil.

I probably need to check again to make sure BUT if ATF, any thoughts on which ATF you would use?   thanks again!   Tom

 

 Hi @tom231. Pinkish purple sounds like ATF. Give it a sniff and see if you can figure it out. To my knowledge, any ATF will work. One can use motor oil, ATF, hydraulic oil, it's the thickness of the oil that affects the dampers rising. Put either ATF or 20 wt in them and after you've had it on the road for a little while, change the oil in the carbs to the unused option and see if there's a difference in acceleration. The oil in the SU carbs acts as a one-way shock absorber. You'll notice when you manually lift the dampers, you've got to push hard to get them to rise but they drop freely. Keep us posted.

Thanks Mark!

Since It is the thickness, is it OK if I happen to mix the ATF with 20W oil?

OR really need to make sure what is in there now and not possibly mix the two?

thanks again!!   Tom

 I suppose you could mix the two but then you'd never know which one works best. Pull the cap from the domes, then remove the domes and carefully lift the dampers out. Dump the oil out. BE CAREFUL NOT TO BEND THE BRASS NEEDLES and don't exchange parts from one carb to the other. Clean all the parts with Acetone or lacquer thinner and reassemble them. Put oil in them, screw the caps back on and then, lift each damper with your finger. They should be hard to push up and fall relatively easy. The rise and fall of the dampers should feel smoooooth.

Thanks again Mark!!

Your insight and expertise is awesome!!

Tom