Briggs Max Lawnmower Carb Query

[andyg0141]

I have a Mountfield Emperor petrol mower from the 1980s fitted with a Briggs Max 4hp engine that has been absolutely faultless until recently. The throttle lever no longer seems to do anything. I have cleaned it all down and it looks fine but its as if there is a spring or something missing but I cant figure it out.

See picture attached. When I manually slide the choke lever on the front, not a think happens to the throttle. I can manually move it when running and it revs fine.

Any advice? Thanks

 

[andymfell]

everything looks to be present and correctly assembled

how the throttle assy works is that the cable pushes the black plastic toothed slider along a slot
this linear movement is turned into rotational movement by the toothed quadrant
this quadrant puts tension on the spring which is connected by the wire link with the ring between the governor arm which is under the cover and the throttle shaft
at the end of the quadrants travel the choke is closed by rotating the small black piece with the round peg

as to what could be wrong
quadrant seized and jumping teeth on sliding part (watch for correct movement when cable operated)
throttle shaft seized or governor seized on shaft ( should be able to manually close throttle when spring under tension)
choke stuck on ( would run very rich )
blocked main jet ( requires removal of carb and float bowl to get at jet in bottom)

 

[andyg0141]

Thanks very much for the info andymfell. It all appears to be moving fine but when moving from full throttle to tickover, there is no movement on the throttle itself. Video attached to try and show what I mean...

https://www.flickr.com/photos/151225950@N03/shares/Buh9A1

 

[Crater Creator]

As andymfell says, looks like the throttle butterfly or governor might be sticking. Does it move by hand?
Tried a bit of oil and wiggle it back and forward a bit?
The spring looks very loose with the throttle closed - maybe try bending it to tighten it up slightly?

 

[andymfell]

maximum RPM is achieved just before the quadrant touches the choke shaft with the blue arrow
at this point the governor spring should have enough tension on it to pull the throttle shaft indicated with the red arrow against the stop in a clockwise direction
when the engine is running the mechanical governor inside the engine is trying to close the throttle against the small throttle stop idle screw with the spring on it .
the operation of the governed engine is a balance between the tension on the governor spring and the action of the governor trying to close the throttle
this can be checked without the engine running by moving the quadrant to the maximum RPM position and manually moving the throttle shaft to the idle screw the spring should pull the throttle shaft fully clockwise
if the engine runs ok but does not rev to enough RPM you can increase the RPM by bending the bracket that anchors the end of the governor spring in the direction of the yellow arrow only bend it about a 1/16th or an 1/8th of an inch as the maximum speed of these engines is 3600RPM and without a rev counter its easy to put too much tension on the spring and over rev them
I guess that somewhere on your mower there is a sticker with a Db noise value on it as a few years ago the manufacturers were throttling back the engines to limit the noise produced


edit I must learn to type faster