Excellent post Vanbcguy... great description of a pretty complicated control system.
It's always tricky to balance power and drivability on a daily driver. I get the feeling that folks are tending to leave the intermediate spring alone and just mess with the main spring when doing the governor mod these days... and your explanation helped show why that might be the case.
Thanks vanbcguy, as vince says a good explanation of how it works...
wow, that was a masterpiece of a post!
I found what I was looking for: page 89 of the 1.5D SAE paper it explains what each spring does to the control collar VS rpm.
there is a difference thou, there are 5 springs:
-idle(part of the linkage) (500rpm to 1000rpm)
-intermediate (the really small one, outside the cage on the governor)(1000rpm to fuel cut)
-part load (small one inside the cage) (the one that makes the car behave more civilized)
-main (the big one, the one we should shim in order to raise fuel cut rpm)
-excess fuel spring (used while cranking, below 500rpm)
rpm is pump rpm
EDIT: cleared some things, there was a mistake
Hey, I owe pretty much all of it to the various VW diesel forums and a LOT of reading!!
You can see why totally disabling the intermediate spring wouldn't really make the car un-driveable, but it really wouldn't help anything. Adjusting the accelerator lever stop a fraction of an inch makes up for anything that spring can do. But I've read a bunch of posts with people saying that they had problems controlling engine speed properly after doing the governor mod - things like RPMs hanging when they got off the power pedal. That really seems to be what the intermediate spring's "purpose" is. The main spring on the other hand has enough travel to more or less completely negate any throttle input you're giving the engine... The "best" way to get the RPM range you want would really be to find the spring tension that accomplishes that, but unless you've got a cutaway pump like in that video and can do a lot of testing it'd be pretty hard to figure out exactly what spring you need. Master pump rebuilders like Giles no doubt have the knowledge to just put the right parts in - I'd bet a 6-pack that a Giles Superpump doesn't have any shims on the main spring!
-Bryn
edit: w00t - this was post #100 for me!