Bill ~ you are spot on & servo/servo feed is frequently the problem but those buggers under the manifold get neglected because they are hard to see & get to. I even found a split rubber elbow on a friends distributor line the other day.

BTW in Aussie speak "crook hose" = damaged or leaking hose.

 

The vacuum capsule itself on the distributor can fail. Years ago, it never happened, but my Daimler has gone through a couple.

 

Glyn
Thanks for picking up on the Australian vernacular. I do try to keep to the Queen's or is it now the King's English when involved in an international gab fest.
But "us colonials" do tend to wander off the path of good language and use our own "patois" especially when expounding our enthusiasm.
Cheers

 

Don't worry Bill. Moderating at MBWorld has taught me not to use SA jargon.

 

Thanks for the technical and language help!
I renewed the seals at both slow running jets 3 years ago with an original SU repair kit, so they should be ok.
By the way, is there a known typical tuned position for the screw of the slow running jet?
I checked the closing of the throttle/butterfly valves by simply looking with a mirror and torchlight. Is there a more sophisticated way?
I will look again for air leaks on the positions you mentioned...
Dave

 

If you release the small nuts and bolts on the apparatus that links the two butterfly spindles the one side should be held closed and tight by the throttle spring. You can then force the remaining side to close using the spindle before tightening the linkage bolts. This is how you balance the butter flies so they are both closed the same amount correctly.

 

I did set up the clamp bolts and spindles just as you described. Nevertheless, deciding whether the butterflies are fully closed is just based on looking with a mirror and light. It’s not a check if they are really airtight.
It would great to hear numbers for the tuned position of the slow running screws (number of rotations before fully closed).
Dave

 

Dave,

I checked my slow runnings screws tonite, Both carbs set at approx. 1.5 turns out from fully closed. I find the idle speed to be set to my preference of about 7-800 rpm.
Personally, I find a too fast idle on any car particularly annoying.
As for the butterfly discs, I would expect that if they are fully closing correctly when testing, the engine would stall ie airflow totally strangulated.
I know from fiddling with SU's on my Coopers, worn throttle spindle will not only allow air leaks, but the discs themselves will not shut off completely, due to sideways movement.
The bigger SU's (HD6 & HD8) probably do not suffer from spindle wear as bad as the 1.25's (HS2), due to their spindle bearing arrangement.
Most Classic Mini SU's are rooted* as this stage of their lives (50-60 years) from worn spindles or throttle bodies.

Pete

* Rooted (Australian vernacular for damaged, worn out or buggered up).

 

Pete,
Thanks for the numbers! Considering the differences in our idle speeds, our screw positions are very similar and possibly typical. You’re right: no engine stall when the screws are fully tightened would be a good indication of having a large air leakage.
Dave

 

My Mk2 had no engine driven ancilliaries (such as PAS, A/C ...). I used to set the hot idle at 500 to 550 rpm (as read from the tachometer). I don't remember it stalling. The idle was extremely smooth and quiet. I'm sure it would have easily passed the threepenny bit test.*

*The threepenny bit was a UK coin with twelve flat sides from the days before decimalisation. If you could ballance one on the top of your engine or bonnet, usually Rolls-Royce, when idleing, it passed the test.

 

Here in OZ that test is far more expensive to perform, we have to use the 12 sided 50c piece

Pete