Why the throttle linkage cam?

[GrahamFountain]

This is a spin-off from the Q about the date for Wax-stat Main Jets, but somewhat off that topic.

Does anybody know, or even have a suggestion for, why the dolomite has that wildly non-linear cam in the trottle linkage, and the TR7 has a simple lever?

Graham

[soe8m]

Yes. You want your pedal to carb progressive. Half pedal is about 25% throttle valve. The other half pedal opens the other 75% throttle valve. This way it makes the car less nervous to drive in city driving etc.

[GrahamFountain]

Okay, but that doesn't explain why the TR7 and TR7 Sprint didn't have one.

Graham

[soe8m]

Okay, but that doesn't explain why the TR7 and TR7 Sprint didn't have one.

Graham

You can also achieve without the cam. The more angled the different levers are the more progressive all becomes. In the drawing i hope to explain. When having both levers on the same spot of their moving circle they behave exactly the same. In the second drawing you can see that with the same pedal travel by your foot the sideway's movement is less so less opening carbs. This way you can make a throttle mechanism progressive and change the relation of opening carbs to pedal travel. The higher in the circle the more travel on the carbs side there will be. Different lenghts of arms can determine the overal travel of pedal that you want. This is schematic but can be used with rods or cables at any place. At the pedal or at the carbs. I did change a lot of these mechanisms on kitcars or self made classic specials which had an on off pedal instead of a normal progressive mechanism. A car can become undriveable by a wrong mechanism.

Jeroen

Scan_20160703.jpg (27.81 KiB) Viewed 707 times

[GrahamFountain]

Interesting. I don't think it's much to do with the pedals in the two cars themselves - though I shall have to go and look at the pedel boxes to see.

I don't think it's to do with the pedals because I've had both TR7 and Dolomite throttle linkages on the carbs of a Sprint engine in a TR7. I've even started with a Dolomite linkage and swapped to a TR7 linkage on the same car, by making a hybrid throttle spindle from a TR7 arm brazed onto a Dolomite choke spindle. And experience says, it makes bugger-all difference to the driveability.

There are two levers in the TR7 linkage joined by a solid rod. I'll go look at the angles between them.

Graham