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Can you please explain how my governor works?


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#1 wahoowad OFFLINE  

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Posted February 07, 2015 - 09:46 PM

I have the hood off my '78 GT18 and have been watching my carb linkage as I operate the throttle. Specifically watching the control rod that connects the carb throttle shaft to the governor.

 

When I increase throttle I see the throttle shaft rotate away from the little spring loaded adjustment screw. The engine RPM's increase like I would expect for the amount of throttle applied, but immediately the governor pushes the control rod back and drops the RPM's back down a good bit. The same thing happens when I give it a little more throttle...RPM increase, then decrease.

 

It almost feels like the governor is over-compensating and not letting the engine develop the RPMs I would expect for the given amount of throttle applied. These are partial throttle increases, maybe 10 to 20% increase, not big jumps. I'm unfamiliar with the governor and don't know if this is normal or not. Engine is a Onan B48M.

 

Thanks for any insight!



#2 Gtractor ONLINE  

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Posted February 07, 2015 - 10:56 PM

Sounds like it is working properly.  If the governor didn't shut the throttle right back down to nearly where it was before the increase, the engine speed would keep increasing to an unsafe level. 

 

They make a hand held tach that has a rubber tip so it can be held against the end of the crankshaft.  Having a gauge like that is the only true way to know you are achieving the correct governed speed. 

If you can't find one of those maybe a local small engine shop would do that for you. 


Edited by Gtractor, February 07, 2015 - 11:00 PM.

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#3 glgrumpy OFFLINE  

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Posted February 07, 2015 - 10:59 PM

I think any throttle adjust makes it's upper move and then drops back by gov if no load on it. There are high idle adjust specs for engines, might check for a book on your engine to get those specs. Then you need a tach tool to see what it is also to be real accurate. Engine does not need to be racing when not working, but come on stronger when bogged down in work. That is govs job.


Edited by glgrumpy, February 07, 2015 - 11:00 PM.

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#4 Auburn David OFFLINE  

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Posted February 07, 2015 - 11:02 PM

It will work different under a load.sounds like its doing as it should,I agree with the other post on this page.


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#5 wahoowad OFFLINE  

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Posted February 08, 2015 - 06:02 AM

So you are saying the gov will also INCREASE speed as engine comes under load? Mostly I am pulling a cart so should expect the gov to increase speed for me (at least to try and maintain same rpm?) when going up a slight incline?
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#6 petrj6 ONLINE  

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Posted February 08, 2015 - 07:11 AM

   Yes, the governor will increase the engine speed and power as you put the machine under load.  you may not even notice it if you are not paying attention, all the others are correct.  as you rev up the engine the governor will throttle it back to keep you in a safe range then when you get into a situation where the engine is losing rpm's due to hi power usage the governor will allow the throttle to open up till it has enough power or reaches max rpm.

                                                                                                                                                                          Pete


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#7 wahoowad OFFLINE  

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Posted February 08, 2015 - 08:04 AM

Hmmm. I will have to ride around and see if I notice the governor increasing speed under load in my 78 GT18. But I know I definately do not see this behavior with my '69 Custom. I always assumed it was beacuse the little 7 HP engine lacked power and thus bogged down easy. For this reason I'm always having to increase/decease throttle almost like a foot peddle as I ride around my slightly uneven yard.


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#8 petrj6 ONLINE  

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Posted February 08, 2015 - 09:48 AM

   It doesn't work exactly like that, The tractor may slow down a bit going up and down hills and such.  it really come into play when you are mowing and snow blowing and really working the motor and the power get bogged down, then the governor will open the throttle to increase power output.  picture mowing the yard and the grass is really hi in one spot, as you are mowing the engine is giving out power that will do the job until you hit the deep grass.  without the governor your engine would bog down and die out but as the engine slows the governor kicks in and opens the throttle plate to maintain rpms and power output then when you get out of the deep grass and the engine begins to over rev the governor allows the throttle to close again to maintain proper rpm's and power output.  it is a bit tricky to figure out.  the basic idea is that if your governor is working properly you wont even notice, but if it is not you will notice the lack of power.

            Pete


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#9 wahoowad OFFLINE  

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Posted February 09, 2015 - 11:30 AM

I don't have a tach but might be able to borrow one from a friend, What kind of tach works for these engines?



#10 Alc ONLINE  

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Posted February 10, 2015 - 06:29 AM

If the governor is working correctly and say your just pulling a cart  1/2 throttle 2000 RPMs and you start a hill will the governor keep opening the throttle to maintain the 2000 RPMs  or close ?   Or does it only come to play when you have the throttle wide open snow blowing , mowing ect ?


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#11 LilysDad OFFLINE  

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Posted February 10, 2015 - 11:56 AM

All my guv'ner does is hassle the Unions. Not what I would call work!

#12 petrj6 ONLINE  

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Posted February 10, 2015 - 05:08 PM

   ALC, the gov will work a little at that point like you describe but you will most likely not even notice.  it really matters when the hill gets very steep or there is lots of weight in the cart. basically when the motor requires lots more power.  Keep in mind most governor's are only a  set of weights spinning around at the speed of the engine, and when the engine rpms decrease enough the weights will swing in or out and open or close the throttle.  so there is a room for error. 


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#13 Oo-v-oO OFFLINE  

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Posted March 01, 2015 - 10:40 AM

To simplify matters, the governor and the governor spring are two opposing forces that want to reach equilibrium. 

 

Let's say the engine is idling and  you set the throttle at about halfway between idle and full speed. When you move the throttle lever, it pulls on the governor spring which is attached to the governor arm. The governor arm then moves toward the spring because you have upset the balance by pulling on the spring. Also attached to the governor arm is a rod that connects to the throttle plate on the carburetor. When the governor arm moves toward the spring, it also opens the throttle which should increase the engine speed. As the engine increases in speed, the force of the governor pulling against the spring increases until they are once again in balance.

Adding load to the engine causes the engine speed to want to decrease. A slight reduction in speed causes the governor arm to move toward the spring again and in turn open the throttle more until the load decreases and engine speed comes back up to the point of equilibrium with the governor spring. The opposite is also true - if load is decreased, engine speed tends to increase and the governor arm will move to close the throttle plate on the carburetor until the forces between the governor arm and spring are in balance once again.

 

 It gets a little more complicated when you consider the geometries involved and the relationship between deviation from target rpm and proportional throttle response. A lawn tractor governor is set up to operate over a wide range of engine speeds while maintaining reasonable control over engine speed. In contrast, a governor on a generator only needs to work within a very small range of engine speeds but must maintain very tight control over that speed so as to maintain proper AC frequency. 

 The geometry of the generator governor force curve, spring rate, and all its associated linkages and ratios are set up to react with an aggressive amount of throttle response to only minor changes in engine rpm. The tractor governor is designed to have a much more linear response to changing speeds and over a wider range of throttle settings. 

 

Mostly what has already been explained, but maybe in a different way. 


Edited by Oo-v-oO, March 01, 2015 - 10:43 AM.

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