In reality the crankcase pressure closing the reeds makes a reversion wave that travels back towards the air filter picking up fuel for a second time as it passes the metering system and almost completely stalling the inward flow. Blue lines represent the reversion.
Now we understand that the actual inbound mixture has a triple metered wave and a single metered wave drawn into the engine. As the wave is drawing fuel on its reversion pass it is also back feeding the fuel circuit and forcing the fuel from the carburetor metering back to the bowl which causes the first 10-20% of the inward bound charge to draw a leaner mixture until the fuel returns.
The strength of the reversion wave is altered not by the crankcase compression of the motor, but by the crankcase volume. It's this reason that a 125cc motor takes a 192 main jet, a 250 is 180, and the 500's a 172 (average jet requirement). Lesser pulse wave strength on smaller motors means less multiplied fuel so an initial larger jet is needed. This lower strength wave makes a pulse unit less effective on small cc motors. It is not uncommon to see the surge of the stock reed boot on a CR500, the appearance of the boot absorbing this pressure does not have any measure able difference when compared to the wave in a rigid inlet like the Boyesen Rad Valve .
A Pulse Induction system replaces the stock boot that mates the reed to carb, its cone shaped chamber traps the majority of the reversion wave (blue) and channels it into the pulse tube where a specific length tube dictates the time for it to be re-introduced as an inbound charge. Metering of the fuel has now been almost perfectly restricted to a single pass of the metering system which no longer is having fuel forced out of it. The single metering pass has now given us an acurate and predictable means of metering the fuel. Commonly the jet sizes need to be increased since they are no longer working on multiplied passes. Throttle response is crisp since you are no longer stalling the inlet stream 1/2 the time
Here you can see the reversion waves time has it half ways back to the plenum while the reeds are still closed.
Timing of the pulse wave set by the length of the tube introduces the wave to the chamber as the reed opens, adding velocity to push the almost stalled inlet stream (red). With the inertia wave more air is introduced than the motor can otherwise draw on its own because it is starting at a velocity equal to what is created 1/3-1/2 of the time into the standard intakes draw, basically its "supercharged". The Pulse system works from idle to high rpm and close to wide open throttle positions since its re-introduction point is post throttle valve. Commonly the engines will not draw fuel consistantly through the rpm range because of the reversion strength, The pulse equipped motors will continue to draw consistantly and evenly to extended rpm ranges not accessable without pulse induction. Intake tempatures are reduced since additional single metered air is aquired and engine tempatures are reduced significantly to where it is reccomended to run a heat range hotter spark plug than normally used.
I've done my best to explain this, I expect questions and have no problem answering them.
Adam Millar
