# jetting on a BF



## browland (Apr 4, 2009)

I see people advertising they have thier jetting at like 140 front and 136 rear or something similar. My question is why jet the front carb with a bigger jet than the rear? Its independant carb, intake . why should the rear be different??


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## browland (Apr 4, 2009)

anybody??


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## FABMAN (Dec 18, 2008)

Its bigger in the rear. The only thing I can think of is if the 2 cyl's were running the same jet the rear cyl would run hotter do to the fresher air running past the front cyl cooling it and the rear getting hotter air and in order to combat this is to give the rear cyl more fuel to cool it. I guess you could run a cooler plug in the rear but that may have adverse effects on the coolant system (overheating)? Dose anyone have a better or different reason?


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## NMKawierider (Apr 11, 2009)

FABMAN said:


> Its bigger in the rear. The only thing I can think of is if the 2 cyl's were running the same jet the rear cyl would run hotter do to the fresher air running past the front cyl cooling it and the rear getting hotter air and in order to combat this is to give the rear cyl more fuel to cool it. I guess you could run a cooler plug in the rear but that may have adverse effects on the coolant system (overheating)? Dose anyone have a better or different reason?


This is the reason exactly...but I think running a cooler plug won't make any difference is overall combustion chamber temps. Richer fuel mix burns cooler, but the rear cylender runs hotter...so it balances. It also has something to do with the exhaust. Some people say after putting on a full...say Muzzy sustem, they are tild by Muzzy to rejet so they are the same. Never saw the instructions so I can't confirm that.


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