Can anyone tell me when I fill the dashpot up (Recomended Redex ) how long is it supposed to last before I refill it?
Iam not sure the problem I have is because there are lots & lots of Hills in Sheffield and I have to put the accelerator pedal down a lot to get "Olive" up the hills but I filled up the dashpot on Tuesday and today ( Sunday ) the redex has all gone!
Ive had a good look and there is NO leaks anywhere.
Paul,
As Brixtonmorris write, the Minor SU's should have light oil (I bought mine from Ware's in Bath - it is labelled as SU oil).
The later SUs (my late metro 1.3) did use engine oil, but that etro semd to empty it's dashpot in two - three thousand miles, well before the service interval.
My 1098 moggie doesn't seem to need much in the way of top-ups (3 monthly), so I guess it's either the Redex (what viscosity?), or wear in the piston/carburetter wall.
I've never had a problem with engine oil in the dashpot - 20/50 is slightly thicker than the original spec, but I'm not sure yuo could tell the difference between a 10-40 and the original SAE20 (if there is a difference ?!?)
The purpose of the oil and plunger IS to restrict the operation of the dashpot so that the engine power rises over half a second instead of a split second. Using a thin oil would allow a fast throttle resonse and lead to jerky behaviour in traffic - with a thick oil yuo would be able to accelerate slowly in a que / traffic jam but with a fast throttle you'd have to slip the clutch to prevent jerking or hitting the car in front.
to get the level perfect, take the airfilter off and lift the throttle slide to the top, then fill to below the threads with the plunger still in. when you let the plunger drop that will be the level you want to fill to next time (without having to lift the plunger). Some carbs have a ring or similar inside to show the level buit doing it this way helps to work out which bit you need to fill up to.
If you fill it any higher it's likely to squirt out of the breather hole!
when you lift the throttle slide, there should be a resistance and it should only move slowly. When you let go, the oil will bypass the plunger and the throttle slide will fall to the bottom sharply. If it doesn't fall sharply you have a problem (probably dirt somewhere, requiring a strip down and a good clean with thinners).
(i think I posted the same time as 57T below ...)
Last edited by rayofleamington on Mon May 03, 2004 11:43 am, edited 2 times in total.
SAE20 is correct as I stated. Would have thought 3 in 1 is too thin. So what's wrong with 20W/50 then or 15W40? The temperature of the dashpot isn't going to rise enough to affect the viscosity that much. SU dashpot oil used to be the ideal but possibly not available now, however don't know what that is (SU oil) mentioned earlier.
Or even this stuff which is MUCH thicker than 3 in 1 which will offer a minimal damping effect.
Useless information time On the locomotive engine governors where I served my apprenticeship, either glycerine silicone (NOT the sealant type), can't remember which , was used as a medium in a piston damper because it's viscocity was hardly affected by temperature. An adjustable needle valve regulated the rate of engine speed increase from 500 - 1250 rpm to 15 seconds. This was a means of protection to reduce the rate of increase so that it was the same at whatever speed the driver opened the accelerator.
I was told sometime back that you put thinner oil in the summer /winter (can't remember which way round though )Talking of dashpots ,my r/r tuner spent sometime smoothing out with wet and dry the bottom of the groove of the slider inside the dashpot (last 1 /4" apparently can get a slight step in it ,which although appears minimal can cause the needle not to go right home in the jet .After he had done mine the needle went home with a definite "click" he thought this was most necessary and spent a fair time rubbing it down
Hello Racer,
can you explain exactly what he was smoothing, as I have always been told never ever ever use any sort of abrasive inside the dashpot or the piston major diameter. The piston major diameter and the dashpot do not touch. (Or they shouldn't so should never wear).
Youre quite right about the fit etc ! He was smoothing the sides and bottom of the guide groove ,witha rolled up piece of wet and dry paper . the groove is about 1 /8"deep and 1 /8"wide .I t surprised me too! but he reckoned even though visually there doesnt seem to be an imperfection,it did sometimes get "notchy " about 1 /4"from the bottom due to constant movement . Bearing in mind my carb also had a worn spindle ,it would seem you only do this to older carbs!PLEASE NOTE this isnt my tech tip,it was something he did .!
Hello Racer,
the penny drops, you are talking about the groove that aligns with the metal tag on the body, which stops the piston rotating. OK.
The cure, by the way, for worn throttle spindles is to keep the throttle wide open, then it doesn't matter.
On the locomotive engine governors where I served my apprenticeship, either glycerine silicone (NOT the sealant type), can't remember which 
, was used as a medium in a piston damper because it's viscocity was hardly affected by temperature. An adjustable needle valve regulated the rate of engine speed increase from 500 - 1250 rpm to 15 seconds. This was a means of protection to reduce the rate of increase so that it was the same at whatever speed the driver opened the accelerator.