Uniflow
Uniflow is a fuel system using two klunks.
It guarantees that the only pressure you get on the fuel line is the muffler pressure,
and cancels out effects of the fuel level in the tank.
The only thing that is not cancelled out by uniflow is the effect
of the distance from the tip of the fuel klunk in the tank to the carb,
so if possible the tank has to be mounted such that the klunk is at same height from
the carb both upside down and inverted.
As you may already know, header tanks have no influence at all on the pressure,
assuming the header tank is full.
Please check other websites to see technical details on how this all works,
for example here.
Installing uniflow is easy with the raptor tanks. Drill a second hole next to the original fuel hole. Put in a piece of thin spring wire through the two holes. Make the two clunks the same length, so that the physical distance between the two is very small. Slide the fully assembled second klunk line over the spring wire. Fasten it with a nut, remove the spring wire, ready!
| Spring wire through the two holes, making a loop inside the tank. | Make the two clunk lines equal in length. |
| Assembled result, Raptor V1. | Assembled result, Raptor V2. |
Note that you now have THREE holes in the tank.
The new clunk line is attached to the muffler. The old pressure hole is now used
for venting: it should be open while filling the tank, and closed before the engine is started so
that the system can build up pressure. The original clunk stays attached to the engine
(or to the header tank if you have one, recommended!)
Few notes to take:
(1) Open the vent hole before fuelling, otherwise you will fill the muffler instead of the tank!
(talking from experience...)
(2) Close the vent before starting, otherwise you won't have pressure and the engine may die in midair
(luckily NOT talking from experience!)