Why is there a 240 main jet in the 376 carb. and 170 main jet in the 276 carb.
They are both for the 500 cc. BSA M20 with an 1" inlet. 
John 
email (option): john.kater@chello.nl
Hi john,
The method of calculating the jet size is different for the 2 carbs,
And jets are also different.
I also checked it once, as it interested me.. 
One method is the showing the flow rate, and the other the "hole" size,
If remembered correctly...
Noam.
email (option): noam10@gmail.com
I managed to find this paragraph on the "Amal" site,
"All genuine AMAL jets are calibrated to a flow rate. The number e.g. 100 indicates that it will flow 100cc`s of fuel in one minute at a specified head. Beware of imitations as they are just drilled to a size. All our jets are branded and packaged with the official AMAL logo."
But could not find anything now about the difference in measurements,
Just that the flow rate is in some cases resumed in the opposite direction
To the real flow, so they the number represent the difference between sizes,
But not the real flow,
And another method is measuring in the correct direction..
nOAM.
email (option): noam10@gmail.com
"All genuine AMAL jets are calibrated to a flow rate. The number e.g. 100 indicates that it will flow 100cc`s of fuel in one minute at a specified head. [/quote]
Noam,
In other words, why does the same engine need more fuel with the Monobloc at (almost) full throttle
John
email (option): john.kater@chello.nl
Hi Johan,
Again, as far as I remember, the 2 jets are not rated at the same way..
One is rated by flow and the other one by jet size, or something like that,
So they are more ore less equivalent,
And there is even a conversion chart..
At least that's what I remember from searching about the subject in the past..
Noam.
email (option): noam10@gmail.com