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Discussion Starter #1
401707 0634 01 81038112

This engine is in my Murray (Avitar)
It's been running erratic ever since I 'refreshed' it last year.

Today I took the skins off to try and figure out what I did wrong in that mysterious Auto-throttle mechanism they buried in behind the carb.

I have the right spring in the 'governor' position. I had what I think is the right spring in the Idle control position. There's only two springs and you cannot reverse them.

When I started it without the skins on I suddenly see why the engine was running away.

The Throttle plate was closed, as in Idle, but the engine was running at full speed????

I'm guessing there is a great deal of fuel and air coming into the manifold under the Carb someplace.
Is there any experienced replies out there?:praying:

16 hp b&s 004.jpg

16 hp b&s 015.jpg
 

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Did you check to see if the throttle butterfly is attached to the shaft or just assumed by the position of the throttle shaft that it was closed? The mounting screws sometimes come out.

Walt Conner
 

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Discussion Starter #3
Thanks Walt. I did look at it while it was racing and it was closed.
I poked at it with a Spring Hook. It was held in place too.
I'll take the Carb off tomorrow and see if I can spot the problem.
Where could all that much air and fuel have come from if that butterfly was closed?
 

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I had a similar problem, not sure it'll be what you have there.....in my case the spacer between the carb and the manifold was leaking air. In my case the carb was also flooding gas into the throat.....the result was lots of gas and a leak of air below the carb, and it was running away. I had to put a little gasket adhesive on both surfaces of the spacer block. And do a rebuild on the carb....fixed mine.

In your case.... who knows.
 

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Discussion Starter #5
Thanks for the Tip. I'll check all that stuff tomorrow.
I'll bet mine is something like that too.

When I moved the Idle air adjusting screw all the way in, the engine kept running as though it didn't notice. I think that means the engine is getting it's fuel/air mix from someplace else.
 

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Are you sure that your governor arm isn't out of adjustment??? i had that happen when i rebuilt my motor i had the arm adjusted wrong and it would run away...just a thought
 

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Discussion Starter #8
Refresh me on that adjustment.
As I recall,
I'm to let the pinch bolt loose.
Let the Governor control arm down all the way; "Top to the right"
Then turn the shaft clockwise to the stop.
Tighten the pinch bolt.
 

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Discussion Starter #9
It was gaskets leaking. The Two bolts holding the Carb down were loose.

Now it will Idle, but nothing in the mechanism returns the Throttle shaft to Idle.
No spring to bring the throttle to Idle position. I have to hold it down with my finger.

It has two springs.
One to the Governor arm (spring is in the middle hole)
The other spring is also connected to the Governor arm, connected to a frame piece, pulling the throttle arm to the wide open position.

When I pull the throttle control arm (in the dash) down to Idle, it looks like a Cam action in the back of this complex throttle control is supposed to move the throttle arm to Idle.
It 'almost' does it, but leaves an 1/8" gap and that gap can get nearly 3000 Rpm out of the engine.

The Book showing my Carb sitting on top the Manifold just does not help at all.
It shows the second spring (A or B) oriented Vertically, which should return the Throttle arm to Idle.
In my tractor its oriented Horizontally. Pulling the Throttle arm in the same direction the Governor arm is pulling it....wide open!
I don't see any place to hook that second spring up in a Vertical fashion.
Is it my Eyes?
 

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Discussion Starter #12
Thanks guys.
I went to both sites. One site only had the Document I already have, Walt's site didnt have anything on this old Critter.

It looks like I'm gonna have to take it all off, make a drawing of the parts and see what I'm missing that way.
I've had this old guy for some years now. It never has worked smoothly or correct as I thought it should. This problem may not be all my doing.

I'll come back when I get something to tell.
 

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Best thing to do might be to look for similar engine and take pict of set up.

IF you can, take pict or two of yours and post it here, maybe we can see what's wrong.

Walt Conner
 

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Discussion Starter #14
Thanks Walt. I think I fixed it tonite and finally understood how the Governor arm works with the throttle.

Bugs drove me out of the barn tonite. Photo's tomorrow. :)

The hand throttle wire would not pull the Throttle all the way back to idle.
I put a slight spring on the Carb to fix that.

When I put the hand throttle all the way open, the Butterfly only opens about two thirds.
Then if the engine slows down from a load, the Governor arm pulls the throttle butterfly open further until the load is off and the springs pull the Butterfly back to the Hand throttle setting.
I put the spring in the Governor arm's Last hole out. Seemingly that should make the engine run the fastest under a load.
 

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It might have an effect on the rpm's and certainly be faster,because it is pulling harder against the governor, but it will mostly react faster to a load, i.e., throttle changes, or heavy grass while mowing. The spring adjusted closer to the governor pivot rod, will cause less reaction, possible loping or hunting until the speed(rpm) settles down to steady rpm's. That position in 3rd hole will work fine.
 

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Discussion Starter #16
It's 98 degrees out right now. I'll test it some time this evening.

I'll have some time inside with the AC on before the evening Thunderstorms roll in.
 

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Discussion Starter #17
bailing wire spring holder.JPG DSCN0200.JPG DSCN0201.JPG


Pretty hard to see any detail down in there. You can see the small return spring and the Bailing wire hook. That pulls the Carb linkage back to idle.

Now with the Governor spring in the outer hole, you just do not notice any difference in RPM as you start up the hill. The Throttle adjustment is instantaneous and the speed or sound just doesn't change. Like an automatic transmission.
 

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View attachment 108945 View attachment 108946 View attachment 108947


Pretty hard to see any detail down in there. You can see the small return spring and the Bailing wire hook. That pulls the Carb linkage back to idle.

Now with the Governor spring in the outer hole, you just do not notice any difference in RPM as you start up the hill. The Throttle adjustment is instantaneous and the speed or sound just doesn't change. Like an automatic transmission.
Bringing back this thread. Sorry about that lol. New to this forum. We just acquired an old tractor (looks to be from the 80's / 90's) with a 16hp opposed twin briggs engine in it. It had trouble running last year and then just wouldn't start up anymore. I just recently did plugs, new coil/wires, carb/fuel pump rebuild (did all the little things with the springs correctly), air filter/precleaner, 5w30 briggs synthetic oil change, lubed up all linkages, etc. It started up on the 2nd crank I guess when new fuel (using 91) got to the carb and sounded great, except I had to pull choke all the way out, give it slight throttle, and then it surges up and down and also revs really high just when touching the throttle a little bit or turning off the choke. I looked inside the carb and checked the linkages and noticed that while the choke butterfly operates perfectly, the throttle butterfly is not synchronized with the throttle (meaning when throttle is all the way down the butterfly does not close all the way, not even close, letting still a ton of air in and why it's revving high I think, and the linkage does not sit on the idle screw.). If I manually close the throttle butterfly from outside the carb with that lever thingy the throttle closes inside. I also made sure the throttle blade was tight and everything cleaned and operating smoothly when I rebuilt the carb. I tried adjusting the screw on the linkage with the spring around it (tightened it as it was way loose) and it did not seem to change much. My main concern is my throttle butterfly is not closing all the way and I'm wondering if there is something that I can do to fix this with the linkage? Is there an adjustment? A tab that needs to be bent? I played with it for awhile last weekend and just started at it while I operated the throttle up and down and trying to pay attention to which parts of the linkage affected what while the throttle butterfly was barely moving, however most of the time it's open and about 1/2 closed if I smack the throttle lever all the way down. Does anyone have any ideas where I can start here? Not sure what model tractor this is as there are no logos or model numbers anywhere unfortunately. Thanks in advance.
 

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Start with two thoughts. The governor will pull the throttle closed AND it pulls against a spring which has its tension set by the throttle control. The spring should hold the throttle wide open with the engine at rest, not running. The governor will bring it down after the engine starts.
So, at idle, the throttle control pulls with minimal tension... the governor can then pull the throttle pretty much as it wants, and it brings the throttle down to the hard idle stop.
With the control at FULL boat, the spring tension is stronger, so the governor cannot pull the throttle plate closed as much. With that match in spring vs governor, the rpms settle at 'something'. Lower the rpm, and the governor tension goes down and the spring keeps its pull, and viola opens the throttle. Once the rpms come up, the governor tension increases, and can again match the throttle spring, and viola once again, the rpm set up at a stable setting.
I do not know this mechanism in the slightest, but all I have seen do something like the above to keep rpms below a 'blow up' setting, and above a 'weak sister' setting where nothing can be accomplished.
I'd suggest putting the springs back whence they came (you DID take a picture, right?), and go through a proper governor adjustment. What happens is you take all the slack out of the governor internally, so the 'paddle' is sitting hard against the spool/spindle, and any motion will start to pull on the throttle spring over by the carb. If loose, the rpms will wander all over, or go to max, depending on how 'stuff' has been attached/moved.
You should be able to move the governor arm against the throttle spring, hand control set at MAX or Rabbit, and pretty much close the throttle. ENGINE OFF.
With the engine running, the governor pretty much is difficult to move manually. They really really want to govern the rpms so you don't expose the gizzards to sunlight via holes in the block, such being fatal to the components.
tom
 
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