is size important ???

[timberman2004]

noticed ...finally,... that there is a difference in the hole in the air intake bell mouth ...

the black plastic ones being some 3-4mm larer diameter than the chromed metal ones

are these engine specific ???

noticed that they can affect performance
my 40 plus (FPC) splutters a bit erratically with the metal bell mouth, but sings well, with either none, or the plasic one

any views ??

[pistnbroke]

The disc with the hole is another hang over from misunderstood technology. all it does is to cause turbulance in the air flow which is bad ..in the old days they thought that turbulance helped mix air and petrol but a smooth airflow through the carb is most important. Bell mouth also acts as minor compressor for incomming air ...turbulance and restriction are causing your splutter ...

[charlesp]

Yes Neal, you're right the later plastic ones have a larger hole, and it does indeed help.

The metal intake could be - and often was - enlarged to make the early Centuries run a bit better.

[timberman2004]

now in my current state of euphoria over the giveaway marston ...

have tried to mix and match these screw on bell mouths

WHOLE NEW THEORY CHAPS !!!
they're like foreskins ......

some engines run better with them missing
some are addicted, and just won't work well without them
some don't care what size the hole is ..as long as it's on

and the ...er...<<discreet cough>>.. Prince Alberts in the flock, only work with a metal one

so much for empirical science

[Collector Inspector]

The size of the bell mouth cover hole is directly in proportion to the negative pressure (Velocity induced) behind it at any given throttle position of various model carbs. In this negative pressure zone, before the slide but after the bell mouth restriction, is a little hole going back into the main jet emulsion tube. This depression resets metering.

Aussie VICTA lawnmower carbs were like this from 1956 up to 74 and believe me, they work a treat on ANY two stroke if ya get caught short the other side of any old black stump..... Must have a restriction to work remember. (Must be a depression, less than atmosphere, before the slide)

They flow and meter air/fuel ratios from 1 to 12 HP requirements with no other mod except for altering "Said Depression before slide"

They self correct depending on what an engine can breath. (Air Pump is any Internal Combustion Principle) New or sadly worn out, makes no difference when set up as above.

I can post diagrams if you wish..........

Villiers just joined in on this and did not tell anyone...."Why"

Regards

B