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Old 11-27-2013, 11:37 AM   #1
ritetwist OP
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Carb springs,r90/6

1974 R90/6. And others of some years.
Any idea why some of the carbs did not have the springs in the carbs above the diaphragms?
I think I read that the springs could / should be put in. There are 2 available, light and heavy.
Recommendations?
Thanks.
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Old 11-27-2013, 11:56 AM   #2
190e
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I have flatop Bings and have often wondered the same thing.



This is just theory but it's my best understanding of how they work.

Springs slow the rise of the pistons which causes a temporary rise in air velocity in the venturi which in turn results in a temporary rich condition or in other words an accelerator pump effect. Using springs should therefore allow leaner mid-range settings without losing acceleration response. In the mid 80's the springs where stiffened perhaps because they needed to stiffen them to compensate for even leaner mid range settings.
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Old 11-27-2013, 02:06 PM   #3
supershaft
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Quote:
Originally Posted by 190e View Post
I have flatop Bings and have often wondered the same thing.



This is just theory but it's my best understanding of how they work.

Springs slow the rise of the pistons which causes a temporary rise in air velocity in the venturi which in turn results in a temporary rich condition or in other words an accelerator pump effect. Using springs should therefore allow leaner mid-range settings without losing acceleration response. In the mid 80's the springs where stiffened perhaps because they needed to stiffen them to compensate for even leaner mid range settings.
I agree except for the reason for stronger springs. BMW never changed the midrange jetting on later models. Same needle. Same position. What they did lean out was JUST off idle by typically going from a 268 needle jet to a 266 needle jet. They leaned out the mains too but that was finally done in an effort to extract maximum power versus playing the situation way safe by jetting the top end WAY too fat which is a real power sponge.
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