In rebuilding the twin SU's, I found out the little plastic bung in the bottom of the piston is for keeping a gap to allow enough air at idle. This gap has to be 12 to 13 thou or the idle will be eratic (according to the chap at Fabre - the importers) This fact is not mentioned in any of the manuals I have on the SU. This bung in a "non servicable part" in other words not available. With mine one was pushed right in and the other had a chunk out of it. The chap at Fabre said the right gap is critical for smooth operation and just happened to have 2 left from a special job he had them made for so I was able to get them for $6 each.

So if your idle is eratic it may not be your cam - check the bridge to piston clearance with the piston hard down.

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David L


My greatest fear in life is that when I die my wife will sell my Mini and tools for the price I told her I paid for them!

hmm interesting its amazing how many little bits and pieces there are that make up these little cars and all or most are critical to get right or the car just isnt right

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Cheers

Hmmm.. I've not played with SUs much for a while- never noticed those bungs before!
Must have been in there though.. to work properly.

Back in the distant past (~1948) SUs had brass pistons, and NO springs..
My dad had one on his Morris 10.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

If just checked my 1 1/2 and true but its more like a bush Black

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Stop Licking the Dog...I Don't Care Who Started It

if ya wanna go back into ancient history doc, they first SU's had a sort of leather bellows that was hand sewn together

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"He's always been a dickhead, He always is a dickhead, He will always be a dickhead. So stop complaining when he acts like one."

Was that SU's Phil, or Stromberg CD's?

This one did have a damper- but the piston was so freakin' heavy it didn't need a spring...

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

hey doc if ya ever at faber midel ask them if ya can have a look in the lab they have some bloody old carby's in there
makka

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Anonymous moderation means the agro that is built up towards the mods isn't aimed at an individual (fewer "Makk" attacks). Less stress for mods means less moderator "retirements".

Well done Wombat. It's not just a "Bump Stop" after all.
There is always something new to learn- compound ignorance- definitely.
The more you know the more you realise what you don't know!

Regards
RonR