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Governor setting and RPM


DaleC

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I remembered the post below and had been thinking about it as to setting up my two engines when tune up time comes.
quote:
I know we have had this discussion before but on must ramble on.Last week I got a digital optical tachometer that has a +or- accuracy of 2%.So it rained today and had nothing to do and put it on all my power equipment.Guess what I discovered.At full throttle most Briggs engines run between 3350-3500 rpm no text book 3600 rpm.Honda's run at3500 rpm and so do Tecumseh.Guess what?At full throttle my 2 Kohlers peaked at 4200 and 4600 rpm.Maybe there is nothing wrong with their rods or lubrication but with their governor springs or factory settings.What do you think?
I was looking through my manuels and found this. I had read it before but with this post on my mind it raised some questions.

It has always bothered me that the 12hp seems to "lope" when driving down the road at full throttle. The 10hp never does. I remember setting the governor springs on other motors before, but for some reason had never thought it necessary to do so on my tractors. The correct operating speed range is 1800 to 3600 RPM. The standard speed setting (no load) is 2900 RPM. Idle speed is 1200 RPM. If I understand this correct. It would seem that the motor, when not underload, should run about 2900 RPM and when the motor is loaded heavy, that the RPM should pick up to 3600. I have used motors that seemed to do this but was not aware that it was by design. Is it by design. If the speed of the engine is not steady. . .,move the spring farther away from the governor lever shaft. This should cure the "lope" in the motor. If the speed variation between no load and full load is too great, move the spring closer to governor lever shaft. Do you think that by variation it means that if the motor is picking up too much rpm then move the spring toward the lever shaft? This just really caught my attention and wanted someone with a little more expertise or no to comment on it.
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Hi, I would be concerned with the 4000 on the Kohlers. They will last a lot longer at 3600. I would need to check the yellow micro-fiche and the type numbers on the Briggs. These vary, I assume a lot has to do with the OEM that has the spec set up. They get spec'd from 3000 to 4000. 34 to 36 is most common with 36oo the most common. A few years ago when the big Broadmore hydro problem existed, we were told to turn the governor up from 3450 to 3600 on these tractors to get the hydro pumps up to speed. The engine were coming from the factory as low as 3100 and 3450 was the spec. Turning them up to 36 helped a lot. As I remember and this is from 35 years ago, the 23D Briggs 9 hp was spec'd. at 3600 and my 243000 10 hp I had was spec'd at 4000. I suspect this is how it became 10 hp instead of 9. My 326xxx s were spec'd at 3600. On the Kohler there should be a little angle stop under the bolt for the pivot arm that connects the governor spring to the throttle cable. Just loosen the bolt and rotate the bracket clockwise a little. You can set the hand throttle to 3600 and shut the key off. Leave the throttle set and then loosed the bolt and rotate the stop up against the arm and tighten. Then recheck. My 2 cents worth, its free, value accordingly. Al Eden
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I suspect the 2900 RPM is a starting point, to be altered according to engine application (within engine specs). For your tractors, this should be 3600. Looking at your profile, I assume you are speaking of Briggs engines. On a properly working governor, the throttle should open and close just enough for the engine to maintain the proper RPM’s. The governor pulls the throttle closed, while the spring pulls the throttle open. With the spring on the far end of the governor lever (away from the governor shaft), the governor has maximum leverage against the spring. When the engine goes under load, the throttle opens very little. So little that it may not be able to bring the RPM’s up to 3600. This is called a low response setting. With the spring on the opposite end of the governor lever, the spring has maximum leverage against the governor. When the engine goes under load, the throttle quickly moves to wide open and the machine may lurch ahead before the governor can pull the throttle down. This is called a high response setting. Compare this with driving your car or pickup up a steep hill. If you respond slowly with your foot on the accelerator, pushing the accelerator down very slowly, you will lose speed before you have the accelerator pushed down far enough to maintain your driving speed. If you respond quickly, by flooring the accelerator, you will immediately increase your speed. What you want to do, is apply only enough pressure on your accelerator to maintain your desired driving speed. If you are driving up an easy incline, your accelerator response would be quite different. If you have one large, steep hill, it would be different than several smaller steep hills. That is the reason for the different holes on your governor lever. You want the governor to open the throttle enough to maintain your engine speed without opening too slowly or too quickly. You want to set it so that it works properly according to what your tractor is used for the majority of the time. If it is mowing and you mow very regularly, you would want lower response. If you mow where there are spots of heavy grass, you want a medium response. If you are mowing tall, heavy grass, you want a high response. Hope this is clear enough to understand. As to your surging, I am more inclined to think that it is a carburetor problem, rather than a governor problem. The governor is often blamed, but is seldom the culprit. Pat
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You also might want to try another spring, sometimes that might be the culprit too. Another thing to keep in mind is that 3600 RPM setting under no load, ie trans in neutral and deck disengaged will not produce 3600 RPM when under load. To get a correct full load speed you need to adjust your high idle speed 5% to 7% above your desired operating RPM. The gap between full load RPM and no load RPM is called droop and the above percentage has been around since the good Lord crossed the river. It applies to gas or Diesel engines whose speed is controlled by spring and fly wheight governors. Tighter droop today is done via electronics. I think Briggs, who is on the lower rungs of the overall HP food chain has gone to stepper motors to get a better grip on tight governing in the stand by generator market, and by this I mean 0 to 1/2% droop, well within 1 HZ frequency regulation, something computers like. He, he, lawnmowers don't care yet.
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Took awhile but ive read this post complete..... My questions, What other carb reasons could be associated with loping, or surging? once a governer is set, should it ever have to be set again? why? Im rebuilding my 16hp briggs carb, should i have to reset the gov.? DougM
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Doug, Loping and surging is most often caused by incorrect fuel mixture, dirt in the carb, a plugged fuel filter, or some other restriction in the fuel system. Once the governer is set properly, you shouldn't have to re-adjust it. As long as the governer was working properly when you removed the carb, there should be no reason that it needs to be reset after a carb rebuild. Pat
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I have experimented. I put the carb off the 10 on the 12 and the motor still lopes. Any suggestions. The twelve on the 10 does not lope.
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Possibly the gaskets between the intake manifold and the block are bad. With the engine running, spray WD-40 or carb cleaner at the area where the manifold bolts to the block. If the engine speeds up or smooths out, you have a leak. Pat
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