ScottAndrews
Well-Known Member
I made a slightly more realistic model after looking carefully at the photos in the OP. Here are two stills of the action of the linkage (the simulator is actually animated). Note the input is ON THE LEFT, so opposite the photo. What this shows is that, barring any physical stop by the butterfly in the carb, the LONGER the linkage arm is, the more the linkage hangs up at WOT,.. Remember, if there is a spring trying to close the butterfly, then once the linkage goes over center, then that spring is working to prevent the linkage from moving back. This is, I believe, the mechanism for the sticking throttle. There is an ideal length of the link to get the maximum throw without going over center.
Here are a couple of screen shots showing the step parameters. The animations are pretty cool (was not able to upload them). The differences between these two are just the length of the linkage "f". The red line is the path of the center point of "f", (marked "P"). Note in the second one with a longer "f" member (linkage) there is a distinct hook at the upper end. This comes from the linkage being over-center. If there is a return force on the output member "b", then the linkage can get stuck there (i.e. at WOT unless there is a larger returning force on the input member "a" to pull it back. You can also see that the longer the linkage "f" the more the red line flattens, which means it takes more pedal movement to get a corresponding change in throttle (that two-stage thing some folks have mentioned).
I encourage anyone interested to go to the 4-Bar Simulator link and try it yourself.
Here are a couple of screen shots showing the step parameters. The animations are pretty cool (was not able to upload them). The differences between these two are just the length of the linkage "f". The red line is the path of the center point of "f", (marked "P"). Note in the second one with a longer "f" member (linkage) there is a distinct hook at the upper end. This comes from the linkage being over-center. If there is a return force on the output member "b", then the linkage can get stuck there (i.e. at WOT unless there is a larger returning force on the input member "a" to pull it back. You can also see that the longer the linkage "f" the more the red line flattens, which means it takes more pedal movement to get a corresponding change in throttle (that two-stage thing some folks have mentioned).
I encourage anyone interested to go to the 4-Bar Simulator link and try it yourself.
Last edited: