fast idle on bs 12.5

[markhaupt]

Model number 289707
type 0121 01
code 9209144f

My 12.5 briggs motor is racing at idle speed. I was wondering if it could be the governor. How hard is it to adjust or replace if needed. Also is it even worth the effort

 

[jakesmurray]

You can blow the engine if you incorrectly adjust the governor. I would recommend taking it to someone who has experience doing it. It does sound like your governor is out of adjustment...

 

[Buckshot 1]

:smile: Very unkikely for the gov to come out of adjustment, unless some one has been messing with it. More likely the gov gear has exploded. The gov gear is plastic/nylon and being that the engine is 11 yrs old, they tend to get brittle from the heat. If it were mine, I would try adjusting the gov lever and if that did not bring the idle down, then take the engine apart and have a look see. Another thing are you sure your throttle control is not froze/hung up somewhere?

 

[markhaupt]

not sure. first time the motor raced, I took carb off to check for torn gaskets, put the carb back on and it ran fine for couple of days and then went back to fast idle.

how hard is it to replace the gov. and does the motor have to come off for it?

 

[Buckshot 1]

not sure. first time the motor raced, I took carb off to check for torn gaskets, put the carb back on and it ran fine for couple of days and then went back to fast idle.

how hard is it to replace the gov. and does the motor have to come off for it?

:smile: When you had the carb off, did you check the throttle shaft movement. I had one in my shop where everyone said it was the governor gear, but upon further checking the throttle linkage, found the throttle shaft had broke into causing it to bind, therefore over reving. Yes, to replace the gov gear you have to remove the engine and open up the bottom end (sump). Also not sure what you are stating with your Not sure statement.

 

[markhaupt]

is there a picture of a properly installed choke linkage on this 12.5 bs motor---everything I am finding is an exploded view and can't quite tell exactly where the linkage hooks onto the carb. Dont know if this will help my problem but found it unhooked at the governor plate. Also can an overstretched governor spring ( part number 690480) cause the fast idle?

 

[Buckshot 1]

is there a picture of a properly installed choke linkage on this 12.5 bs motor---everything I am finding is an exploded view and can't quite tell exactly where the linkage hooks onto the carb. Dont know if this will help my problem but found it unhooked at the governor plate. Also can an overstretched governor spring ( part number 690480) cause the fast idle?

:smile: There is only one way to hook linkage to the choke shaft. There is either a Z end or hook End on the linkage that hooks on the choke shaft. From the IPL, looks like the other end just slides into the control bracket. The gov spring on the gov linkage is to provide tension, therefore should not cause the fast idle. Is there two separate controls, one for the throttle and one for the choke or choke and throttle together?

 

[markhaupt]

There is only one lever where the choking mechanism is on the top end of the throttle lever. On top of the choke valve on the carb, there is a hole on the motor side of the plastic piece and a hole on the outside part of the plastic piece. It appears that the linkage hooks into the hole on the motor side but I just want to make sure. Also when the motor is running at high idle, i can manually move the governor control lever and the idle will disipate. Is this indicative of the internal part of the govenor being bad. I am just trying to isolate the problem before tearing the motor apart for something that may have been solved without having to remove the internal part of the govenor.

Thanks for any advise.

 

[Buckshot 1]

There is only one lever where the choking mechanism is on the top end of the throttle lever. On top of the choke valve on the carb, there is a hole on the motor side of the plastic piece and a hole on the outside part of the plastic piece. It appears that the linkage hooks into the hole on the motor side but I just want to make sure. Also when the motor is running at high idle, i can manually move the governor control lever and the idle will disipate. Is this indicative of the internal part of the govenor being bad. I am just trying to isolate the problem before tearing the motor apart for something that may have been solved without having to remove the internal part of the govenor.

Thanks for any advise.

:smile: Correct choke linkage to the engine side. Manually moving the lever is a tell tale sign of internal failure but there could be other causes. Check the idle adjustment screw postion on the carb, maybe screwed in to far.