Brendan -
That was a good description of the damper action and its effect on engine performance. I learned something else, too. With the dampers in place, remove the air cleaners and lift the vacuum pistons with a finger through the carb intake with the engine off. Feel the resistance for each piston, and if they are wildly different the engine won't run right upon acceleration. It's because one of the damper pistons (the little piston) is worn more than the other. The fix is to replace one of the damper pistons - usually the one where the vacuum piston rises with little resistance because the damper piston is not doing a good job. Before conducting this test, of course check the dashpots to see if the oil levels are correct and the same. - John
> There is a Government conspiracy to keep
> this information from the public
> I have a Series 2 Jaguar manual (for bigger
> SU's) in front of me that says to use SAE 30
> motor oil for the piston dampers in the
> Recommended Lubricants section, but doesn't
> mention its' use anywhere else, nor how full
> the damper oil should be - Refitting
> is the reverse of the removal
> procedure. Ha! My Z and 1600 (510)
> manuals are just as helpful. Anyway...
> Datsun/Nissan recommended SAE 10 motor oil,
> but SAE 20 will work and some people
> recommend it for worn carbys. I
> personally think that the damper pistons
> never wear this much (but the main-piston to
> suction chamber seal does wear!). However, a
> FAQ I found somewhere says:
> You can also modify your car's throttle
> response
> characteristics slightly by adjusting the
> viscosity of
> the oil in the dashpot damper. SUs are set
> up
> so that a thicker oil will resist the
> piston's attempt
> to rise in the dashpot for just long enough
> that the
> engine's increased load (when the throttle
> is
> opened) will pull more fuel across the
> bridge; this
> enriches the mixture and temporarily bumps
> power
> up to help the engine achieve higher speed
> more readily.
> Still no mention of how high to fill
> There is an SU FAQ for MG's at:
>
> <A HREF=http://www.british-cars.org.uk/kimber/mgoc/emg/basic4.html>http://www.british-cars.org.uk/kimber/mgoc/emg/basic4.html</A>
> that says:
> Top up each of the piston dampers with
> carburettor
> damper oil. Unscrew the damper cap, withdraw
> the
> damper and top up the reservoir until the
> oil level is
> 1/2 in (12mm) above the top of the hollow
> piston rod.
> my '72 dampers have two lines scored in each
> above the damper pistons that *may* be
> dipstick marks...
> My personal opinion is that it doesn't
> really matter how full the damper oil is as
> long as the piston is submerged when the
> engine is off (thus it will always be
> submerged because the main
> piston/damper-resevoir rises). 1/2
> above the damper piston sounds good.
> Brendan.
> PS. Hope my terminology wasn't too
> inconsistent. As each SU has a piston within
> a piston it gets hard sometimes
