Originally Posted by triton thrasher
Longer intakes can improve performance.

Long rigid intakes between carbs and head can cause bad vibration effects in your carburettors.

Longer intakes can also adversely affect performance.
There are a couple of ways that inlet port length affects performance
1) Ram pipe effect, the port will have a column of mixture travelling at high speed when the inlet valve is open. when the valve closes this column keeps moving due to its inertia and causes a high pressure area of mixture behind the valve, when the valve opens this mixture is released into the cylinder. Unfortunately at lower RPM this column can stall and the longer the port the harder the engine has to suck to get it moving again.
2) Tuned length, the port length can be tuned the same way as an exhaust pipe to utilise the pressure waves created when the valve opens and closes
3) Friction, the longer a port the more of the mixture is in contact with the port wall. The friction between the port wall and the mixture slows down the charging of the cylinder.
An experiment to try, take a 100M length of say 5mm bore tube cut say 20mm off the end. Blow through the 20mm piece of tube, it's easy. Now blow through the 99.98M length, it will be rather difficult

BSA B31 500 "Stargazer"
Greeves 200 "Blue Meanie"
Greeves 350
Greeves 360
Suzuki GSX1100 EFE "Sorcerers Apprentice"
GM500 sprint/LSR bike "Deofol"
Jawa 500 "Llareggub"
Aprilia RSV Mille "Lo Stregone"
'35 & '36 OK Supreme
Kawasaki ZZR1400 "Kuro no senshi"