I have compression release on my Beta 230cc trials bike. These were common on bikes back in the 70's and 80's and were often used for braking. When I pull the release from say 40 mph it slows me down FAST. Almost as effective as good brakes. How does releasing the compression slow the bike so well? Doing so will stop the firing process but so will hitting the kill button which has little effect on slowing the bike. It seems to me that with no compression the bike would not slow much if you chopped the throttle at 40. What an I missing? I was going to remove the release when I got the bike but it's way too effective.
If the compression release is not activated, the compressed air above the piston will return the energy needed to compress it and push the piston down. Similar to bouncing a B-ball off the floor. With the compression release activated, the compressed air above the rising piston is pushed out of an opening, and when the piston passes TDC and starts the downstroke, there is no returned energy pushing the piston down. You are releasing the energy required to compress the air on the upstroke, sort of like trying to bounce a B-ball off the floor that will not hold air pressure. I never liked B-ball.
They also can suck dirt if you use them as a engine brake, unless you set up a filter on the bleed port.
With the decomp open put your finger over the bleed port on the piston down stroke. It sucks in air, not as much as it releases but it still allows in unfiltered air
Think of a syringe pushing air out of the tiny hole and then having to suck the air back in during downstroke.
