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Discussion Starter · #1 · (Edited)
I tried posting this about a day ago, but I must have posted in the wrong forum ... post disappeared ... anyhow,

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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
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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 lose 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 is intact
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?


I placed some photos and videos to help debug the issue at the following spare URL of mine:

B&S Engine Debug Support
 

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Yeh!!, I know, I gave an answer and I have been searching the whole of tractor forum for the last 24 hours trying to find your post, stranger things happen.

I mentioned for you to check the inlet manifold from the carby mount to engine mount and in between looking for an air leak, I was able to watch your video and I feel that the manifold could be sucking air, has this happened with the new carby?, or was this happening with the old carby also?.

You could also remove the air cleaner from the carby throat and peer inside to see if the throttle butterfly is closed against the inlet throat of the carby, both sides of the butterfly should be against the throat.
 

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Discussion Starter · #3 ·
Started happening after about the 4th mow with the tractor. Before that the idle just seemed high to me.

The connection between the carb and the engine was checked when I disassembled the intake manifold to check that the throttle valve (butterfly) did not come loose and made sure it was not sitting on 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.

Since you made the suggestion, I will disassemble and double check (today) and post back.

"You could also remove the air cleaner from the carby throat and peer inside to see if the throttle butterfly is closed against the inlet throat of the carby, both sides of the butterfly should be against the throat. " ... With he air cleaner off (photos & videos) I can only observe the linkages on top of the carb. I would have to remove the carb to see the butterfly
 

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OK, so you are not really worried about the high idle, just that the throttle lever wont increase the engine revs when pushed to the rabbit position??, ok down behind the throttle slide mounting on the side of the engine, there should be a short fat spring connecting the governor lever to the throttle slide lever, that is either stretched or missing, have a look down into the housing between engine and slide.

Don't worry about the fine spring that is fitted to the throttle rod, that is to stop the throttle from bouncing around and causing the engine to run uneven.

Hood Motor vehicle Vehicle Automotive design Automotive tire
 

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Discussion Starter · #5 ·
Hello FredM,​

Sorry for the delay.

You have it half correct:

The current major problem is the throttle lever won’t decrease the engine RPM's when pushed to the turtle position.

I’m afraid after this problem is resolved, my original problem may still exist in that the engine idle is too high.

I think you are talking about the governor spring. Seems to be hooked-up on both ends and intact. In high throttle position (rabbit) the spring is stretched leaving a lot of tension on the mechanical governor linkage (throttle rod). In low throttle position (turtle) the spring is NOT stretched leaving little to no tension on the mechanical governor linkage (throttle rod); this is the position that concerns me (no low idle). See images below:

Hood Automotive lighting Automotive tire Motor vehicle Bumper


Governor Spring High-Throttle Stretched (tight)

Motor vehicle Automotive tire Automotive wheel system Engineering Gas


Governor Spring Low Throttle Relaxed (loose)
Wait, I just took apart the plastic intake manifold (50B in the following image) and I appear to be missing gasket 51A where the plastic intake manifold connects to the engine. It Must have been missing for a long time (or never had one in this model) because I did not remove this part to install the carb. 51A looks like it may be for a different engine with that non circular center, this just might be an artist error and they left this in from a previous diagram they may have used to start from. If the gasket looked like 51, then I would not have any doubts. What do you think?

I also checked that both gaskets were not staked together in location of gasket 51.

Hand Arm Leg Human body Jaw

Intake Manifold Gaskets

IF I ORDER GASKET 51A

Should I order gaskets 51A or do you think gasket 617 is good enough to seal against flat metal of the engine?

Is there any way to test if this is what is causing the (stuck in high idle) problem before I wait for gasket 51A and finding out that this gasket is not for my tractor?
 

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Is there provision for an O ring 617 between the manifold and the cylinder head, or is the O ring on the carby, if there is a flat gasket 51A between the manifold and head, then you could make your own with a little bit of perseverance to check for the problem.

I guess the carby is off, did you check the throttle butterfly to see if this is closed up against the carby throat, unscrew the idle screw to make sure the butterfly closes.
 

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Discussion Starter · #7 · (Edited)
Is there provision for an O ring 617 between the manifold and the cylinder head, or is the O ring on the carby, if there is a flat gasket 51A between the manifold and head, then you could make your own with a little bit of perseverance to check for the problem.

I guess the carby is off, did you check the throttle butterfly to see if this is closed up against the carby throat, unscrew the idle screw to make sure the butterfly closes.
O ring 617 is present I'll attempt to create a temp gasket and try to see if 51A is required and will fix the problem

thanks for your suggestions , I will keep you informed of my progress.
 

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Gas Auto part Machine Tool Font

This should be the governor setup like your engine, is the governor spring connected like in this image?.

this spring is what increases the engine revs when you push the throttle to rabbit and when you bring the throttle back to turtle, the governor action brings the engine back to idle.
 

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Discussion Starter · #9 ·
View attachment 80475
This should be the governor setup like your engine, is the governor spring connected like in this image?.

this spring is what increases the engine revs when you push the throttle to rabbit and when you bring the throttle back to turtle, the governor action brings the engine back to idle.
Yes, that looks like the control bracket and all its peripherals. So, it is the governor that controls low idle. Well, something is not governing correctly in this engine.

Just to be as complete as possible, on the previous (missing?) intake manifold gasket, I actually found I had a second #51 gasket that I placed on the intake manifold instead of #51A as shown in the diagram. 51A looks like it is for a different engine. After adding the gasket, when I started the tractor (in my garage) the throttle appeared to be controlling the idle (high and low). I reassembled the tractor and backed it out on the driveway to let it warm up before trying to mow the lawn. After a couple of minutes, I was back to the extremely high idle with no throttle control.

Hand Arm Leg Human body Jaw


But this time I noticed something different. If I engaged the blades, the engine idle did drop a little and I was able to reduce the top RPM’s down so I could actually mow my lawn. I used the tractor for about 45 minutes (0.47 acre) and the engine gave no other sound except for higher-than-normal RPM that I was able to compensate for with the throttle (only worked when the blades were engaged … engine under load). Once I disengaged the blades the engine would race up to that high RPM and the throttle would have no control (stuck in high idle).

So, now we are in territory that I suspected, and I was hoping we would not arrive. I suspect the governor is intact otherwise I would hear the governor parts rattling around in the engine (I could be wrong ... broken parts could have found a nice hiding spot away from the cam shaft and timing gear). But I am getting ahead of myself, before I tear the engine apart to replace the governor, is there any debug that can be performed to rule out external parts?
 

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Before you go tearing into pulling the engine down, start the engine and at idle or slightly above, place your finger on the governor lever and increase the engine revs, do you feel resistance when you pull the lever?, and another, if you pull the lever to increase the engine revs and let the lever go, does the lever quickly return to the idle position?, if the answer is yes to both questions then the governor is working as it should, if you have to push the governor lever back to idle position, then I would say the governor is not working.

I have asked if the throttle butterfly is closed against the carby throat a couple of times and have received no answer, I also suggested to unscrew the idle screw when doing this check just to make sure the butterfly is resting against the carby throat.

I feel your troubles are with this Chinese carb you have purchased, my suggestions were to try and resolve your problems by checking possible faults in the system.

The problem with the throttle lever when pushed to the rabbit position and not pulling the governor lever to increase engine revolutions as it should suggests the spring is stretched enough to not overcome governor counter weight pressure on the governor shaft with the engine running, I did see the throttle linkage move in one of the videos when the throttle was pushed to high idle position.

I have looked at your photos a number of times and watched the videos, and all show that the throttle butterfly stop is resting against the idle screw, which in my opinion could be unscrewed more, anyway, it is hard to make assumptions from photos and written words.
 

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Discussion Starter · #11 ·
Before you go tearing into pulling the engine down, start the engine and at idle or slightly above, place your finger on the governor lever and increase the engine revs, do you feel resistance when you pull the lever?, and another, if you pull the lever to increase the engine revs and let the lever go, does the lever quickly return to the idle position?, if the answer is yes to both questions then the governor is working as it should, if you have to push the governor lever back to idle position, then I would say the governor is not working.

I have asked if the throttle butterfly is closed against the carby throat a couple of times and have received no answer, I also suggested to unscrew the idle screw when doing this check just to make sure the butterfly is resting against the carby throat.

I feel your troubles are with this Chinese carb you have purchased, my suggestions were to try and resolve your problems by checking possible faults in the system.

The problem with the throttle lever when pushed to the rabbit position and not pulling the governor lever to increase engine revolutions as it should suggests the spring is stretched enough to not overcome governor counter weight pressure on the governor shaft.

I have looked at your photos a number of times and watched the videos, and all show that the throttle butterfly stop is resting against the idle screw, which in my opinion could be unscrewed more, anyway, it is hard to make assumptions from photos and written words.
Thanks for you reply, I will try your suggestions tomorrow and i will disassemble the crab and check that butterfly.
i still have the original carb also. ( surging issue)
 

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Discussion Starter · #12 ·
Okay, I would like to thank you for your help so far.

I added a few videos to my test website again link is here




But to save some time and maybe some boring video viewing, I’ll try to surmise with the videos showing.

First, I was able to check the governor because all they do start the engine at this point and I believe the governor was acting the way you described in your last post.

To get the visibility you requested of the butterfly in the carburetor, I just disconnected the carburetor from intake manifold.

I was able to see what you’re talking about now.

The way the set screw was positioned the butterfly did not close all the way.

So, I adjusted the set screw so the butterfly would close, buttoned up the carburetor, and turned on the engine

So, the butterfly now closes all the way and when starting up the tractor it seems to be running correctly right now; the high and low seems to be working.

Now I’m back to the original problem I was trying to correct. What I think is an abnormally high RPM at the tractors high idling (throttle).

I guess the last thing I did was screw around with that set screw on the carburetor. Now that I know I can not get any low RPM adjustment that set screw and not to screw around with it.

Is there any adjustments that you know of that can be made to the carburetor (or other) to lower the high RPM (rabit)?

If not, do not worry about this I can always run the tractor at ¾ to 7/8 throttle to back off the upper RPM while mowing.

Thank you again for your help and time you put into this
 

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The Briggs engine is factory set to run at 3600RPM, if you haven't fiddled with the governor clamp bolt on the bottom of the governor lever, then the engine should not exceed those revolutions, probably pay you to get one of those combination rev counter/ hour meters and mount on your machine, it is just a matter of wrapping the pickup wire around the high tension spark plug lead and mount the unit in a good place.

Shop around for one of these units, I imported mine from China with a few weeks wait for about $14 au, the retards here in Oz are asking up to $45 au ea, and that is way over board in my opinion.



And if you had of just unscrewed the idle screw, it would have saved you a lot of trouble and time, but hey!!, that is the way of things.
 

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Discussion Starter · #14 · (Edited)
The Briggs engine is factory set to run at 3600RPM, if you haven't fiddled with the governor clamp bolt on the bottom of the governor lever, then the engine should not exceed those revolutions, probably pay you to get one of those combination rev counter/ hour meters and mount on your machine, it is just a matter of wrapping the pickup wire around the high tension spark plug lead and mount the unit in a good place.

Shop around for one of these units, I imported mine from China with a few weeks wait for about $14 au, the retards here in Oz are asking up to $45 au ea, and that is way over board in my opinion.



And if you had of just unscrewed the idle screw, it would have saved you a lot of trouble and time, but hey!!, that is the way of things.
If I only knew I had caused the problem ... lack of experience

And I did muck with the governor clamp, but that was after the original high idle problem
thanks again for your assistance

Thanks for he link, I will see if I can find a US substitute
 

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Discussion Starter · #16 · (Edited)
I guess we will need to reset the governor link, do you know how??.
I had adjusted it (after fiddling with the idle set screw on the carb) according to a video on YouTube.

How To Properly Set the Governor On A Small Engine - With Taryl

Time on Video: (4:17 - 7:36) adjusting the governor
Taryl Fixes All

Seems knowledgeable.
I am not sure why the guy has a costume on (at least I hope it is a costume).
Maybe he wanted to be an actor.

if you know of a better video, or if this guy is totally wrong, please advise.

I am ordering the tach / hour meter for the tractor.
Probably will not adjust the governor until I get the meter.

Is the 3600 RPM at low throttle or high throttle?
 

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To adjust governor, NOTE applies to any governed engine, Move speed control to wide open (full speed, rabbit, or what ever you call it) with this done the governor spring should be stretched. Loosen the pinch bolt (or linkage adjustment bolt) Note which way the governor lever moves to OPEN, Turn the governor shaft as if were moving the lever in that direction until it stops. Tighten bolt. To check if you did it correctly, move speed control to slow (idle, or turtle) governor and throttle lever on carburetor should move to idle. When complete start engine and set idle speed by adjusting the screw on the carburetor that controls the throttle plate.
If high idle (wide open, rabbit) is incorrect the bottom arm on the governor needs to be bent to set the speed. stretch spring = faster shorten spring = slower
A governor functions by balancing the flyweights inside the engine against the spring outside the engine. When the "set" speed changes either the flyweights or the spring attempt to maintain the set speed. The governor/carburetor are synced when the flyweights are forced closed and the carburetor is wide open. When the engine starts and speed increases the flyweights apply force to the external lever which closes the throttle plate until the spring balances the force or the idle screw stops movement.
I myself have a hard time reading words and understanding mechanical workings here are some videos that might help.


 

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I had adjusted it (after fiddling with the idle set screw on the carb) according to a video on YouTube.

How To Properly Set the Governor On A Small Engine - With Taryl

Time on Video: (4:17 - 7:36) adjusting the governor
Taryl Fixes All

Seems knowledgeable.
I am not sure why the guy has a costume on (at least I hope it is a costume).
Maybe he wanted to be an actor.

if you know of a better video, or if this guy is totally wrong, please advise.

I am ordering the tach / hour meter for the tractor.
Probably will not adjust the governor until I get the meter.

Is the 3600 RPM at low throttle or high throttle?
The high idle (rabbit position) is 3600RPM.

Taryl knows his job, but he likes to ham a bit.
 

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Question of the day- What causes the engine to surge at idle.

The engine surges at idle due to a restriction in the idle circuit of the carburetor. Why? The engines leans out, it slows down, then the governor opens the throttle, engine speeds up, governor slows engine down---repeat ---- repeat -- repeat ---
The same can happen at wide open throttle if the idle circuit or the load circuit is restricted causing a lean mixture. It will clear up under load (usually) due to more fuel coming thru the load circuit.
Due to pollution regulations manufacturers have the engines leaned out. Also note again to the government pollution regulations the adjustment screws have been removed or made nonadjustable on the carburetors. So if the remnants of old gas or a piece of dirt restricts a jet the surging is the result and you cannot adjust the carburetor to compensate for the restriction. Ether need to clean (if possible) or replace the carburetor.
NOTE an air leak around the carburetor mount, intake manifold or a worn throttle shaft can cause surging. Also be aware the idle circuit is functioning even when the engine is wide open throttle, but the load circuit only functions when the throttle is open far enough to cause it to function due to lowering the vacuum in the venturi of the carburetor.

 
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