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Small engine question: revs way too high now

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  • Small engine question: revs way too high now

    I have a riding mower with a B&S 20 hp Intek engine, a little over 10 years old. (Change oil & filter religiously, oil is proper type and at proper level.) I was mowing yesterday, and had to shut down momentarily. When I went to start it up again, the engine sounded very strange. I took my hearing protection out and it seemed to be revving very fast for being on idle speed.

    I examined the linkages and springs around the carb, thinking that maybe a spring broke, a linkage came out, or a twig worked its way in there somehow. Nothing appeared to be out of place. I suspect the governor inside the crankcase busted apart, and no longer provides "slow down" input to counteract user throttle input.

    My plan is to get a service manual for this type of engine (B&S 273521) to pull the bottom of the crankcase and examine the governor, but want to check in here for advice first. Any tips before I dig into this engine?

  • #2
    Re: Small engine question: revs way too high now

    Can you manually control your throttle speed? At idle your governor should be doing nothing except sit there and simply exist. If it is an internal governor, it is centrifugal, it will not make the mower idle faster. Does the motor seem to run any faster than usual at wide open throttle? If it is idling too fast, I suspect the problem is with the carburetor or related linkages. Did you get the engine part number off of the shroud? I tried looking it up online for a parts list and came up empty handed. The number you gave comes up as a repair manual.
    We don't have preventative maintenance around here, we have CRISIS MANAGEMENT!

    Comment


    • #3
      Re: Small engine question: revs way too high now

      Originally posted by masterbeavis View Post
      Can you manually control your throttle speed? At idle your governor should be doing nothing except sit there and simply exist. If it is an internal governor, it is centrifugal, it will not make the mower idle faster. Does the motor seem to run any faster than usual at wide open throttle? If it is idling too fast, I suspect the problem is with the carburetor or related linkages. Did you get the engine part number off of the shroud? I tried looking it up online for a parts list and came up empty handed. The number you gave comes up as a repair manual.
      Yes, the part I referenced was the repair manual for this type of engine. The engine model is 406777.

      I'll recheck the linkages and springs. With the engine off and throttle lever set to idle, the carb butterfly should sit against the idle adjust screw. If it is and it still runs fast, then it must be carb, right?

      Comment


      • #4
        Re: Small engine question: revs way too high now

        Too many times to count, I have seen the throttle butterfly come loose from the throttle shaft.
        I have also often seen the governor's flyweights come off the governor gear.
        Needs a bit more observation before suggesting a course of action.
        "HONK if you've never seen a gun fired from a moving Harley"

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        • #5
          Re: Small engine question: revs way too high now

          Originally posted by Doctordeere View Post
          Too many times to count, I have seen the throttle butterfly come loose from the throttle shaft.
          I have also often seen the governor's flyweights come off the governor gear.
          Needs a bit more observation before suggesting a course of action.
          Ok, I don't think the governor inside the crankcase is the issue. I say this because I can see the lever arm move back and forth and equalize when I manually tweek the throttle shaft.

          I changed out the fuel filter and fuel lines. The filter was a little discolored, and the lines were cracked and brittle. That didn't solve the problem. Also checked the fuel shut-off solenoid: clicks open when I put power to "on" and closes when "off."

          I'm starting to lean more toward the throttle plates having came loose. A loose butterfly would admit an uncontrollable amount of draft air, and pull too much fuel in, perpetuating the speed problem.

          Comment


          • #6
            Re: Small engine question: revs way too high now

            Originally posted by JoePolvino View Post
            Yes, the part I referenced was the repair manual for this type of engine. The engine model is 406777.

            I'll recheck the linkages and springs. With the engine off and throttle lever set to idle, the carb butterfly should sit against the idle adjust screw. If it is and it still runs fast, then it must be carb, right?
            LOL. silly me! I thought that was the model of the engine. I tried looking up the model number to see if the governor was internal or external, all it kept pulling up was the repair manual.
            We don't have preventative maintenance around here, we have CRISIS MANAGEMENT!

            Comment


            • #7
              Re: Small engine question: revs way too high now

              Update: I ended up pulling the carb and cleaning out the channels with carb cleaner. The throttle plates were solidly attached to the shaft, and there was no play in the shaft. I did notice that once side of the carb had a bit of discoloration, and suspect this was due to the breather occasionally depositing a fine oil mist, and the draft just channeling more to one side. Besides that, no varnish, no deposits, very clean inside.

              The fact that this issue was very sudden, as opposed to a gradual problem, leads me to believe that there was a mechanical malfunction. I'm leaning toward thinking that maybe one of the governor counterweights may have come off. I say this because the engine does govern well at idle, but doesn't seem to have the strength to pull against throttle demand at higher speeds.

              Anything other suggestions? Thanks.

              Comment


              • #8
                Re: Small engine question: revs way too high now

                so what you are saying is that now the idle problem does not exist but now it over speeds the motor? Sometimes I overlook things and need clarification. Worst case, take it apart, inspect the governor, re-seal the motor while you have it apart.
                We don't have preventative maintenance around here, we have CRISIS MANAGEMENT!

                Comment


                • #9
                  Re: Small engine question: revs way too high now

                  Originally posted by masterbeavis View Post
                  so what you are saying is that now the idle problem does not exist but now it over speeds the motor? Sometimes I overlook things and need clarification. Worst case, take it apart, inspect the governor, re-seal the motor while you have it apart.
                  I'm sorry, I forgot to mention: I did adjust the governed idle by adjusting a tang. So now it idles ok, but still has the speed problem. If my theory about the governor breaking is true, then maybe I just covered up the low speed symptoms.

                  Comment


                  • #10
                    Re: Small engine question: revs way too high now

                    Popped open the engine last night and my theory about the busted governor was confirmed:

                    Comment


                    • #11
                      Re: Small engine question: revs way too high now

                      Hey, Whadya know? Good thing those pieces did not get sucked into the rotating parts.
                      We don't have preventative maintenance around here, we have CRISIS MANAGEMENT!

                      Comment


                      • #12
                        Re: Small engine question: revs way too high now

                        Actually, it turned out to be a little worse of a situation since I wrote the update.

                        The left side of the shaft is supposed to be pressed into the crankcase, and the gear is supposed to rotate freely on the shaft. The gear seized up on the shaft and ended up spinning it within the cavity it was supposed to be pressed into...you can see the wear on the left end of the shaft where this happened.

                        So now I have to somehow free the gear from the shaft, press the shaft into the engine block cavity, and assemble the new governor gear onto the shaft. Any advice on how to press it in, maybe add some loctite to keep it there? My BIL is a welder, so how about a couple tiny weld dots on the shaft, and then grind/sand so they have enough to bite?

                        I'm also interested in how to assure that the gear won't freeze up on the shaft again, so I may end up using extra fine sandpaper on the shaft just to give it more clearance around the gear...the shop didn't have a replacement shaft so I have to re-use.

                        Would an oil additive like marvel mystery oil help keep things more slippery? I change my oil every spring and replace the oil filter as well, so I don't think this is a case of neglect.
                        Last edited by JoePolvino; 04-25-2012, 12:50 PM.

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                        • #13
                          Re: Small engine question: revs way too high now

                          I think your best bet is going to be to get another engine.
                          sigpic

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                          • #14
                            Re: Small engine question: revs way too high now

                            Originally posted by NHMaster3015 View Post
                            I think your best bet is going to be to get another engine.
                            Yeah, I suspect I'll try to get another couple years out of it, and then get something else. This is 11 years old.

                            Comment


                            • #15
                              Re: Small engine question: revs way too high now

                              Originally posted by masterbeavis View Post
                              Hey, Whadya know? Good thing those pieces did not get sucked into the rotating parts.
                              my son had rebuilt a Chevy 400, when he was in HS, and he took it out for a test run and at that time was not aware the 400 would not handle the RPMs with stock rods as the increased stroke would do a number on the rods, any way about a mile from the house the engine blew, and the largest piece of the one piston that got sucked down into the rotating parts was no bigger than a quarter, the hole in the side of the block was bigger than a quarter, but he learned a lot from the experience,
                              Push sticks/blocks Save Fingers
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