Hi All,

My Sport is running very rich and the rear carb 'piston' is too high letting too much fuel in at idle.

I should remember this but alas, age has crept in.........

What is the correct oil type to use in the SU style carbs? And how much do you put in?

glenn

Hi Glenn
I am sure the purist will yell at me as there is an official SU pot
Oil however
I use traditional ATF (not the modern low viscosity stuff)
Another alternative is fork oil 15 weight
The volume is only small and there should be a small mark on the dip stick dampening rod (less than 10ml off the top of my head perhaps)
Cheers
J

Thanks for the reply. Not sure what that is. ATF. Or available from super cheap or similar stores?

I think way back i might have used auto trans oil. Ok on the mark on the stick.

The rear one i staying about 1/4" or so open and i can petrol being sucked in out of the neddle and seat area. Puilling the plugs, they are wet. Plus lots of exhaust smoke.

Tomorrow I will see if i can get that oil

glenn

ATF = Auto Trans Fluid
Unless I am mistaken….
The oil is for dampening so at idle it shouldn’t really come into pay as it works to dampen the slide in the carby according to changing vacuum…….it would come into play when you try to take off from idle under throttle which can cause stutter….
Have you checked if the slide is sticking or the spring is damaged?
Alternatively you may have a sunk float….
J

Yeah i suddenly remembered what ATF was after i shut the PC down......

Everything seems ok when i remove the top0 of the carb. Spring looks good etc. I also thought might be float level. Car was running just fine before i went out for a few km trip when is occurred, running rough as. And obviously over fueling by the new plugs and seeing the excess fuel going into the engine... damper pot or whatever its called sticking high. About to check the oil levels when i get some ATF! And float although both were replaced when i got the car on road.... hard to believe its now in 11th year. i have had it

glenn

Well, after pulling both carbies to bits looking for 'issues' found nothing wrong. Although the rear needle was about about 3mm different to the front one. PLus the screw holding the needle in was loose. Which I thought might be the issue.......But No.

Then I looked a bit closer (well a lot) at the choke mechanism. The short of it is that the rear carby choke wasn't always going right off.

Glad it's sorted Glenn, sometimes it's the simple things.
Oil I used in my Crown S Aisans was machine oil, like seeing machine oil. It would gradually lose some until there was no damping effect, and the piston would jump up too quickly, causing rough acceleration.
Cheers,Matt.

Hi, I always use ordinary 20/50 engine oil.
Gr Dick