# Craftsman YT3000 Lawn Tractor with B&S Model 331877 Engine … Stuck in High idle



## djslota (May 10, 2021)

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Craftsman YT3000 Lawn Tractor
Model: 28851, 42" 21hp Briggs & Stratton Turn Tight™
B&S Hydrostatic Yard Tractor Engine:
Model: 331877 
Type: 2371G5
Code: 110822ZD


*Back ground*: Last year about ½ way through the mowing season, my tractor would surge in any throttle position (low to high) under no load.
As soon as I put the tractor into high throttle, and engaged the blades, the surging stopped and the tractor ran great.
Not wanting to not have the mower out of service for primary lawn cutting and leaf extraction season, I just ran the tractor this way for the last ½ of 2021.
At the beginning of this season (March 2022), I ordered one of those knock-off Chinese carburetors and swapped out the original Nikki carb (which I have read are a pain to rebuild).
The surging stopped and the tractor ran great; there was one problem though, the engine sounded like its idle was higher-than normal.
I tried adjusting the idle speed with the only adjustment screw on the Chinese carb, but that resulted in only increasing the RPM’s greater than where I started.
While I was investigating how to adjust the high RPM’s, I would run the tractor at about 7/8 throttle, while mowing, just to bring the engine RPM’s down to what I thought was a more normal idle.
After about my 3rd lawn cut with the new carb, I noticed that the throttle stopped working completely.
It appears to be stuck in (rabbit mode) full throttle.
While the tractor was stuck in high throttle (won't go into low idle when moving the throttle lever)

*I noticed the following:*

Throttle cable is intact and operating perfectly
The (only adjustment on the carb) idle adjustment screw on the carb has very little effect on adjusting the RPM’s lower
The (idle) butterfly in the carb is NOT loose or residing in the intake.
governor linkage spring is intact and connected to the governor control lever and the throttle shaft, that controls the throttle valve, on the carb
the spring partially surrounds the mechanical governor linkage
*Additional Notes:*


It seems like when I perform a static adjustment of the governor, there are stops as expected in both directions (clockwise and counter clockwise)
With the throttle is in the high (rabbit) position, the governor spring is stretched and there is a tight governor control lever
With the throttle is in the low (turtle) position, the governor control lever (on the carb) is loose and the governor spring is not stretched
Although I have no control over the throttle and the engine appears to be idling very high, I do not hear any noises from the engine to indicate that anything has come loose or is broken in the engine. In fact, I could (but won’t until I find the problem) probably cut my lawn if it wasn’t for the lack of RPM control.
I do not have a tachometer (RPM meter)
*Here is the question of the day: What controls the engine idle when the throttle is low (turtle mode) and the governor spring is not stretched?*

Support Photos and Videos​


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## djslota (May 10, 2021)

One more video just added - showing throttle moving from high to low videoing the linkages while he engine is not running.

Last Video on Page​


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## FredM (Nov 18, 2015)

Check the inlet manifold from carby to engine for an air leak.


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## djslota (May 10, 2021)

FredM said:


> Check the inlet manifold from carby to engine for an air leak.


Thanks for your suggestion, but the connection between the carb and the engine was checked when I disassembled the intake manifold to check that the throttle valve (butterfly) had not came loose and was in the intake of the engine. When reassembling, I verified that the intake gasket on the manifold side, the intake manifold O-ring and the intake gasket on the carburetor side were in good shape and proper installation.

Remember, besides the higher than expected idle, for 3 mows after replacing the carb, the throttle worked perfectly.

But, since you made the suggestion, I will disassemble and double check.


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