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  • Throttle governed engine.

    This is going to be something a bit different. Most of you will have a fairly good knowledge of how a hit and miss engine runs. On a hit and miss engine, the governor disables the exhaust valve when the pre-set rpm is surpassed, holding the exhaust valve open and letting the engine coast until the engine slows down, at which point the governor allows the exhaust valve to close and the engine will once more be able to build compression and fire. However, there is a different way of governing an engines speed for engines which are not "hit and miss" types. In this type of governing, the governor opens and closes the butterfly valve in the carburetor to adjust the engine speed. In a perfect world, you "dial in" the speed at which you want the engine to run. If the engine speed slows beyond that point, a linkage from the governor opens the butterfly valve in the carburetor and admits more air/fuel mix to bring the engine back up to the "dialed in" rpm setting. If the engine rpm exceeds the "dialed in" speed setting, the governor closes the butterfly valve, thus starving the engine for fuel until it slows down to the dialed in rpm. I have a twin cylinder opposed engine that I built a few years ago, which has a manually controlled butterfly valve in the carburetor. I also have a governor which was salvaged from the very first "hit and miss" engine which I designed and built. (The engine ran, but was horribly unbalanced). Over the course of the next few weeks, I am going to try and "marry" the two bits of technology to end up with a "throttle controlled" engine. Follow along. It should be interesting.---Brian
    Brian Rupnow

  • #2
    Why not rig up a connection to try the twin engine for a quick test, manually operating the throttle? It would be a shame to do a lot more work only to find this engine also lacks enough power to drive the edger. IF it won't run it manually operating the throttle, a governor isn't going to increase the engines power output. Your choice, the end result will be the same either way.

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    • #3
      Not a bad idea Sparky. I have to do a bit of tune-up/clean-up on the twin engine first, before doing anything else, and I may set it up with my tachometer and see what speeds I can get out of it. I know that when I built it I could get about 850 rpm at idle, but it's set up on the shelf for a long time.
      Brian Rupnow

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      • #4
        Originally posted by brian Rupnow View Post
        Most of you will have a fairly good knowledge of how a hit and miss engine runs. On a hit and miss engine, the governor disables the exhaust valve when the pre-set rpm is surpassed, holding the exhaust valve open and letting the engine coast until the engine slows down, at which point the governor allows the exhaust valve to close and the engine will once more be able to build compression and fire.
        Well I guess my knowledge of a hit & miss engine was not so good. I always just assumed it was the intake side that was disabled as needed (i.e. power NOT needed) to permit coast mode. Thanks for that clear explanation Brian.
        Lynn (Huntsville, AL)

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        • #5
          You're welcome lynnl. Before I dive into this one, I want to set up the twin cylinder engine and make sure that I can tweak it manually to give a high speed of 2000 rpm and a low speed of about 1500 rpm. I have a laser tachometer and can measure rpm quite accurately. Last night I lay in bed thinking about this. If I don't want the engine to ever exceed 2000 rpm, that can be accomplished by a hard-stop on the throttle linkage which doesn't really involve the governor. I would like to have a "mode" where the governor is disengaged so I can start the engine with the throttle closed and the governor completely "locked out" where the engine will run at about 850 to 1000 rpm . When I have the engine started and do engage the governor, I would like the governor to take the rpm up to around 1500 and hold it there under a "no load" condition. As soon as a load comes onto the engine and the flywheel shows the smallest inclination to slow down, I want the governor to immediately open the throttle fully, not incrementally, and take the speed up to full 2000 rpm and hold it there until the flywheels are no longer seeing a load and the engine can drop back to 1500 rpm until the next load is applied.
          Brian Rupnow

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          • #6
            Originally posted by brian Rupnow View Post
            . If I don't want the engine to ever exceed 2000 rpm, that can be accomplished by a hard-stop on the throttle linkage which doesn't really involve the governor..
            Problem I see there is that the hard stop limits the carb opening and when under load there will be times you want the carb wide open to get max power.

            Think of a hard stop on your cars gas pedal, no problem with normal driving really BUT if you have a trailer behind you and are starting from a stop on a hill, you will need to go beyond that hard stop to get enough power to get the car/trailer rolling. Once at speed, the hard stop likely wouldn't be a problem.

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            • #7
              Another thought reading your description of proposed operation. Farm tractors / construction equipment etc. have BOTH a governor and a throttle. The throttle level sets the desired rpm, the governor maintains that RPM constant under greatly varying loads. The engines are governed at everywhere from idle to full throttle, the term governed meaning maintaining the rpm constant under varying loads. The governor is not a single RPM device.

              THEN there are governors that are single RPM devices, like for use on a electric generator, they hold the rpm at one preset rpm, never changes. (normally 1800 or 3600 depending on if its a 2 or 4 pole generator)

              Two different types of governors. Your application is much more like that of the farm tractor.

              Little food for thought in bed tonight
              Last edited by Sparky_NY; 12-19-2019, 10:32 AM.

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              • #8
                I mean, go look at any small gas engine sold today that gets used on lawn mowers or garden tractors, or go carts. Look at how the governor is setup

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                • #9
                  Originally posted by RB211 View Post
                  I mean, go look at any small gas engine sold today that gets used on lawn mowers or garden tractors, or go carts. Look at how the governor is setup
                  Couple styles used there, one is mechanical with weights driven off the crank or cam, the other is a "paddle" mounted up near the flywheel that deflects from the airflow coming off the flywheel cooling fins. The paddle type I am assuming is popular because its a lot cheaper to implement and on a lawnmower or similar where tight rpm control isn't really that critical.

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                  • #10
                    Originally posted by Sparky_NY View Post

                    Couple styles used there, one is mechanical with weights driven off the crank or cam, the other is a "paddle" mounted up near the flywheel that deflects from the airflow coming off the flywheel cooling fins. The paddle type I am assuming is popular because its a lot cheaper to implement and on a lawnmower or similar where tight rpm control isn't really that critical.
                    Yup - the air vane control or paddle type will rap out at higher RPM's at warmer temperatures or high altitudes where as the mechanical weighted ones are much more stable in all conditions...

                    It's why you will only see the mechanical weighted one's on things like gensets where RPM needs to be held very close to either 1800 or 3600 rpm's

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                    • #11
                      The difference here is going to be the very even sound of course. The hit and miss is so captivating on a desktop engine because of the unique interrupted sound of it. A throttle governed engine will just sit there purring with a steady sound.

                      Having broken in a few dozen model airplane engines over the years there's a little bit of young boy in the rear of the brain that can't resist jazzing the throttle a little here and there instead of just letting the engine be. So perhaps a nice feature for this new engine with the throttle governed setup would be a fairly obvious spot to jazz the revs on demand and easily without having to reach in to some dark spot. That'll make it a touch more interactive.

                      That initial drawing shows a really slick looking engine. Lots of eye candy on this one. Not that any of your engines are ugly. But this one with the exposed rockers is going to have some great appeal to it with all the wiggly bits wiggling away.... This will certainly be a fun project to watch taking shape.

                      I don't know why but this engine sort of reminds me of the old steam tractor engines. Ever have any thought about building something like an old iron wheel farm tractor and putting RC gear into it for something like this?
                      Last edited by BCRider; 12-19-2019, 11:44 AM.
                      Chilliwack BC, Canada

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                      • #12
                        I know about 80% of what there is to know about governors. I know about the airflow governors on Briggs and Stratton engines. I know about the flyball governor style used on steam engines. I know about centrifugal weights driven off the crankshaft. I have at one time or another built and ran all of them. One of the problems is deciding how to add it to an existing engine without making it look goofy. I do appreciate you fellows stepping up and offering your advice. Thank you.
                        Brian Rupnow

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                        • #13
                          You can avoid the mess with linkages and just go smooth operating cable, also that way you can tuck the govie away neatly any where you want it...

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                          • #14

                            Since my twin cylinder engine is a few years old now, and has ran a lot, the first thing to do is to run a few diagnostic checks. The attached drawing and explanation will give a pretty good way to check the valves and rings on each cylinder.


                            Last edited by brian Rupnow; 12-19-2019, 12:46 PM.
                            Brian Rupnow

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                            • #15
                              Put a gauge on it and you have a poor mans leak down tester, the modern way of the same test. Leak down not only tells there is a leak BUT also how bad it is by the rate the pressure leaks down.

                              Wondering why only 20 psi? Do you figure your engines only have about 20psi compression?

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