New Pipes and Carb Adjustments

[Jack Klarich]

There is always a pressure drop across the air filter. The better the filter flows, the less the pressure drop. This pressure drop causes a slight vacuum, pulling in more gas. Put on a higher flow filter, and you reduce the pressure drop and vacuum, pulling in more air and less fuel. This is why you can run leaner with higher flow air filter.

Since most exhause is IR(Individual runner) and not a shared system, reversion can also make a difference in what the cylinder sees. And since both intake and exhaust valves are open at the same time during overlap, the carb can actually "feel" the pulses from the exhaust, and this too can change jetting requirements.

(In my racing days I've cured backfiring problems by going longer on header pipes)

Good info and makes sense:s

 

[Hoople]

There is always a pressure drop across the air filter. The better the filter flows, the less the pressure drop. This pressure drop causes a slight vacuum, pulling in more gas. Put on a higher flow filter, and you reduce the pressure drop and vacuum, pulling in more air and less fuel. This is why you can run leaner with higher flow air filter.

So a more restrictive air filter would be like "choking" the carb and once you installed a free flow filter, the A/F would in fact get leaner. Then stack that with what Brian said about the early carbs being lean to start with and you could have a situation that needs to be re-jetted.

Great info. Tks!

 

[fin_676]

So a more restrictive air filter would be like "choking" the carb and once you installed a free flow filter, the A/F would in fact get leaner. Then stack that with what Brian said about the early carbs being lean to start with and you could have a situation that needs to be re-jetted.

Great info. Tks!

The early carbs were a lot richer and they went lean in 1992
jet sizes from softail service manual
49 state model 1991
main jet - 185
slow jet - 45

49 state model 1992
main jet - 165
slow jet - 40

Brian

 

[Jack Klarich]

The early carbs were a lot richer and they went lean in 1992
jet sizes from softail service manual
49 state model 1991
main jet - 185
slow jet - 45

49 state model 1992
main jet - 165
slow jet - 40

Brian

Good info here Brian, Yep the lean carbs would hicup at cruising speed from too lean, 92-97 carbed Baggers did for 1 week til I re jetted them

 

[Terry Jackson]

The early carbs were a lot richer and they went lean in 1992
jet sizes from softail service manual
49 state model 1991
main jet - 185
slow jet - 45

49 state model 1992
main jet - 165
slow jet - 40

Brian

Both my 96 and 02 sportsters had the 40/165 combo, and ran lean. The 02 had the screaming eagle breather & exhaust and would barely run 70. Changed both to the 45/185 combo, and added the washers to the metering, and it's like I doulbed the motor size, and no more backfires.