Originally Posted By: Tim H.
Originally Posted By: dwendt44
the governor controls the RPM no matter what kind of oil is in there.
The governor is set at ~3000RPM. The engine will run at 4000 easily.
It may run smoother, quieter, etc.. but not faster.
It can be set to run faster, but a change in oil won't do it.
I have to disagree. If the Governor was electrical (like the modern day FI engine controls are), then yes, I would agree, but as a mechanical governor, the 3000 rpm has a +/- to it, and changes in oil viscosity can affect it, but not enough for the mechanical governor to catch it. Case in point is some engines running slightly slower when cold (oil thicker) than when hot (lower viscosity). My Honda mower will run slightly slower for about the first 2-3 minutes before RPM rises, even though it is governed at 3000 all the time.
There could be other explanations for that besides cold oil. Do you actually expect that the extra load from slightly thicker oil (ie. "thin" 10cSt M1 vs. a 12+cSt ACEA A3 30 weight) is going to cause any measurable difference in engine load compared to engaging the blade and cutting grass, as far as the governor is concerned? I'm not sure why so many people expect the resistance from an oil slinger to present so much load on small engines.....
Alternative explanations for running a little slower when cold started include variance in the governor itself. If it's an air vane type, for instance, it'll be blowing cold ambient air instead of heated near-engine air for the first while. That colder air is more dense and thus fewer RPM is required to push the vane to the "set point" RPM. Just an example to get you thinking, I have no idea of the specifics of your units.
Another alternative may be that the revs are not actually lower, but larger throttle angles may be required. This extra intake noise when under no load compared to when at full operating temperature may make the pitch of the machine sound lower. Have you MEASURED the RPM with a tachometer, or are you going by ear?
