A friend has been trying for months now, with the help of others and some rolling road work done,to try and get the  tripple Su,s he has put on his car to work.

the car is a 2.0,litre , six cyl with  a fire order of  1.5.3.6.2.4, and a  280 deg cam,

the prob he has got is blow back, /fuel stand off of the carbs.

some folk have come to the conclusion that because of the fireing order, then 3 sets of carbs of the SU type will not work

the standard set up is twin SU/Stromberg carbs

he has tried putting in a bigger balance pipe, but is no better

3 x twin side draughts, or FI will work, but these are different from the constant depression carbs like the SU.

any one any  experiance with tripples on an engine with this fire order.

It's been many years since I worked with SU's and, I have not done three, but I have done several race cars with two.  The "standoff" you speak of is quite normal and I doubt you would like the performance even if you could eliminate it.  My normal procedure was to us air horns (trumpets-Resilient Seated Gate Valves) that were just long enough to catch "most" of the visible standoff mist.  On an MG or Sprite, that was something like two to three inches...it varied with displacement/cam/rpm, etc.
Street machines always had an air filter and I assume the standoff problem was not as critical at lower rpm.  On the race cars adding the trumpets made a big difference.
Perhaps you could use a K&N type filter over them.

Some things that come to mind (wow, that's a stretch!)...Using different viscosity oil in the dashpots and or springs could and sometimes did help.  The richer the mixture the more standoff (well, DUH) and on these little engines the needles looked like "sewing" needles!!!

I think you should consider the basic cause of "standoff" - fuel mist/spray coming out of the carbs. The only apparent cause would seem to be the excessively late closing of the intake valve allowing the piston to push the fuel/air mixture back out of the intake tract when the engine is not "on the cam". Is the cam maybe not actually a 280 but but something with more duration? Is the cam still not installed correctly?
 Having said this I have seen helical cam engines demonstrated idling with the intake valve closing at around 110 degrees ABDC with no sign of fuel spray coming out of the carbs - so maybe "standoff" can have other causes.
What is the cranking-speed compression pressure? This should give some indication of how "big" the cam is or if it is installed correctly.

I don't think base circle runout affects cams with tappet clearance much - if at all. Runout does affect hydraulic tappet cams very much though.

On the subject of balance tubes - I have never seen a one-carb-per-cylinder motorbike engine that had a balance tube (or any interconnection) at all - so it would seem that the size etc. of the balance tube is not very important.       

Big vlad the base circle can be a problem we have seen as much as 12th rise on base circle caused by bad grinding, the effect is to close the tappet setting and leave the valve of the seat causing what looks like stand off. Opening the tappet clearance is a quick way of checking
if this is the case if you are at the rollers. beleve me it
not as uncommon as you might think, its just it gets missed.

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