Hi Guys,
Did some governor mods this weekend.... well, lets just say It was a pretty interesting experience!!
Problem:
The original spring I was using was giving me fair response and stability, but was a little "hitchy" in the upper power range causing quite a bit of lag under heavy load.
Started by making a stud to link the spring to on the governor arm, then moved the adjuster from the one side to the other - the adjuster is now on the "fixed" side of the governor spring. This allows for a much easier and reliable method of setting engine RPM while it is running. While I was at it, I removed the stud that the spring was originally affixed to and made the mounting space for the spring virtually the full width of the crankcase, attaching it to the lower camshaft cover bolt - this allows for a whole range of springs to be tried(Which I of course did...)
My Findings:
A long spring which is fairly soft, but tensioned to the original tension of the spring that I was using - This caused major hunting with the linkage setup as it was. I changed the linkage lengths and got them to as good as I could with this "long and soft" spring - virtually perfect under low loading, but under high/full load the engine started to hunt.
Conclusion: A long spring is not always the best for every situation - I shortened it down in stages and found matters improved, but were not as good across the range as they were before.
Solution:
I then replaced it with the "Original" spring that I was using and found a marked and vast improvement to the governing - the problem with hunting disappeared(Long/Soft Spring) and having "tweaked" the linkages to as good as they could be with the long and soft spring, this in turn improved the setup on the original spring throughout the power range.
Conclusion: A longer/softer spring will show up linkage length problems and pronounce them to a degree that they become easier to sort out - it is easier to hear a 100RPM hunt than a 20RPM hunt(for me anyway). Be careful you don't overspeed when it starts hunting!!
Once you have got the linkages set up as best you can, then you can concentrate on the spring tension/pull ratio to get the revs to where you want them - Be prepared to change springs as it is not only the tension of the spring that matters, but the tension/stretch ratio that determines how the engine responds and gives it the required power "stability" across the range. If the spring is too soft/long - the governor weights fly out just a little to far and they seem to go "over-center" and it takes a major rev dip for them to drop back into their "linear" operating area.. If the spring is too short and hard, when you get the ....... well.... I didn't get a chance to go into these waters..... With a Rainstorm pissing down and a sense of humour about to fail - I stopped testing when it was doing what I wanted it to!! (Always a good excuse-If you have fixed the problem, stop fixing it some more!!)
Note: The "Original" spring I was using was not the one that came with the engine - I had put a more suitable spring on to de-rate from 1000 to 750 RPM in the beginning of the "Lister Journey"
Hope this helps someone, somewhere, sometime.....
Regds
Ed