+- Austinsevenfriends (https://www.austinsevenfriends.co.uk/forum)
+-- Forum: Austin Seven Friends Forum (https://www.austinsevenfriends.co.uk/forum/forumdisplay.php?fid=1)
+--- Forum: Forum chat... (https://www.austinsevenfriends.co.uk/forum/forumdisplay.php?fid=14)
+--- Thread: SU Oddity? (/showthread.php?tid=3899)
SU Oddity? - bobthompson - 14-02-2020
OK, will one of you clever chaps explain this to me:
Moderate tune Chummy. 1 1/4" SU. Semi downdraught. Pumped feed.
Tuning on the road with an AFR meter on a Lamda on the downpipe.
Steady, fairly steep hill. Holding 5000rpm flat out in 2nd gear. AFR steady at 12.3, happy! Holding same revs around left hand corner and AFR drops to 12.0. This was repeated a couple of times.
What's going on to make it go richer on corners?
What's the cure?
RE: SU Oddity? - Ruairidh Dunford - 14-02-2020
Is the piston lying towards the engine or the outside of the car?
RE: SU Oddity? - bobthompson - 14-02-2020
Sorry - I don't understand the question? The piston can only fit one way because it is slotted.
I forgot to say it is an HS2 carb.
RE: SU Oddity? - Ruairidh Dunford - 14-02-2020
Which way is the piston leaning?
RE: SU Oddity? - bobthompson - 14-02-2020
The carb. leans towards to the engine, bolted to a Raeburn ally manifold
RE: SU Oddity? - Ruairidh Dunford - 14-02-2020
I suspect the carb leans towards the engine and on a spirited left hand bend it will be pulled further that way, which will richen the mixture slightly - maybe??
RE: SU Oddity? - John Mason - 14-02-2020
I don’t know if this is part of the oddity but cornering particularly at speed can alter the gas flow in engines. The petrol/air mixture goes with centrifugal force differently through the manifold as it is forced to the side of the innards of the manifold. Not so much with straight engines like our sevens but shows up more on V engines when the outside bank of pistons run rich and the inside bank runs lean.
John Mason.
RE: SU Oddity? - Alan - 14-02-2020
I think what R is getting at is the centripetal force causes the piston to rise slightly thereby richening the mixture.
RE: SU Oddity? - Ruairidh Dunford - 14-02-2020
That is my guess, based on the OP, Alan.
RE: SU Oddity? - spannerman - 14-02-2020
Float chamber is it upright or at a angle ?