Posted by Clint Dixon [172.70.126.199] on Sunday, November 21, 2021 at 19:07:53 :
In Reply to: You can adjust the governor for altitude? posted by DDD [108.162.215.135] on Saturday, November 20, 2021 at 16:54:54 :
I have seen no written directions for altitude adjustments anywhere within governor sheets, shop manuals, or service bulletins. I do not have any military manuals. I am speaking strictly from the civilian information I have.
The difference between a very low barometric pressure day and a very high barometric day can cause the air flowing through a velocity type governor to have a slightly different force upon the throttle plate that it is flowing across. This can in turn cause the governor to allow the engine to run at bit faster or slower maximum governed speed. My WDX with the integral velocity governor in my ET4 Carter Carbureter can see a difference in up to a 5mph maximum speed difference between low and high pressure days. But, this is not reliant solely upon the barometric pressure. The temperature and humidity differences that tend to follow swings in barometric pressure also play a slight role. And other aspects of engine performance are also effected by humidity and temperature. It is not entirely the fault of barometric pressure.
The barometric pressure differences resulting from changes in altitude are compensated for within the actual carbureter in jet sizes. This is to allow for more oxygen in the fuel mixture at higher altitudes where the air is thinner, and for less oxygen in the lower altitudes where the air is heavier.
Adjustments to velocity type governors do not have a direct effect upon the amount of oxygen in the fuel mixture. These type of governor adjustments only determine the point at which the throttle plate will stop opening any further by a creating an adjustable mechanical influence upon that point at which a balance will be reached between the air passing (and trying to close) the throttle plate, and the internal springs allowing a hard stop to move out of the way of (and allowing to open) the throttle plate.
Velocity governors tend to work well until something inside gets worn or breaks and then they typically do not work at all. Depending upon what wears or breaks inside will have the effect of either allowing the engine to rev higher than normally desired, or allow the engine to rev no higher than an idle.
I feel the advice of others has about covered what you should be looking for. I think at this point that the governor should be the least of your worries.
Junior