Oscillating idle - 8N

[timsch]

I recently cleaned the carb and attempted to adjust it after reinstallation. It starts easily with minimal choke, runs pretty well, but when I pull it down to idle, it oscillates. I don't recall it doing that years back. Here's a video of it, showing the governor arm moving back and forth. What could be the cause of this, assuming it's not typical.

 

[R Geiger]

Does the idle screw have an effect on it? Sucking air around throttle shaft?

 

[timsch]

Not sure. May not be able to check on it for a couple of days.

 

[NMNeil]

Disconnect the linkage from the carb to the governor. If it idles fine when disconnected it's unlikely that the carb is the problem.

 

[McNugget]

I recently cleaned the carb and attempted to adjust it after reinstallation. It starts easily with minimal choke, runs pretty well, but when I pull it down to idle, it oscillates. I don't recall it doing that years back. Here's a video of it, showing the governor arm moving back and forth. What could be the cause of this, assuming it's not typical.

Check for a vacuum leak - spray some carb cleaner around the mounting flange while it is oscillating and see if it evens out.

 

[soaked]

Hi timsch,
You have recieved fine advice already posted.
Looking close on your video im seeing the gov output link rod to the carb is bent. See screenshot from your vid.
Its supposed to be straight as an arrow. A Farmerized repair, when the governor is worn, is to give the rod a bend.
Not sure its at fault for oscillation, but its likely goofing up the bottom 1/3rd on the quadrant. The governor output arm is closer to the carb than it should be for a given rpm, and that's messing with flyball force vs spring tension equilibrium.

 

[used red MN]

Let me add this, hold the throttle shaft/carb linkage still if the engine still hunts the problem is the carb adjustments/internal fuel and air circuits need cleaned or there is a vacuum leak as suggested. If once you get the engine to run steady with the carb linkage held if you release it and it starts to hunt the linkage or the governor also have a problem.

 

[timsch]

Thanks everyone so far. Weather has prevented me from getting back to this, but once I do, hopefully later this week, I have these much appreciated pointers.

soaked - I'll look into correcting that bend. It's been like that since I got it 10 years ago.

 

[soaked]

Likely it was bent rather than spending money on gov parts.
I'm in western wa, and we've only got down to 23° overnight, and mid 40s for highs. Hope your not single digits.

 

[timsch]

Finally got back to this. Carb spray around the mating flanges had no effect. Disconnecting the governor linkage from the carb and holding that carb arm steady, it ran smoothly w/o hunting.

The carb was recently fully rebuilt and adjusted prior to my 1st post here, so fuel passageways should be clear.

 

[Jim L WA]

Looks like it's time to overhaul the governor. But first check the governor spring tension.

 

[Mad Farmer]

Looks like it's time to overhaul the governor. But first check the governor spring tension.

Look over all the linkage connections carefully for wear/slop too.

 

[showcrop]

The small adjusting screw is for air. Out for more in for less.

 

[timsch]

Hi timsch,
You have recieved fine advice already posted.
Looking close on your video im seeing the gov output link rod to the carb is bent. See screenshot from your vid.
Its supposed to be straight as an arrow. A Farmerized repair, when the governor is worn, is to give the rod a bend.
Not sure its at fault for oscillation, but its likely goofing up the bottom 1/3rd on the quadrant. The governor output arm is closer to the carb than it should be for a given rpm, and that's messing with flyball force vs spring tension equilibrium.

So what problem is bending the output link supposed to be correcting?

 

[soaked]

Overspeeding.
Likely your gov is too long in the driveshaft gap .220"- .230" spec, allowing the flyballs to orbit into the housing, cutting a groove. Bending the link rod kicks the gov fork forward, closing the orbit diameter, allowing the balls to climb out of the groove, and begin "pushing back" against the cone shaped upper race.

 

[timsch]

I got the governor apart and found that there was a groove, but so shallow in most places it looked more like a track with no real depth. There were sections of the track where material had slightly worn away, but was not uniform. Initially, I thought, "great, no groove, and all should be well" after feeling it, but then noticed that the balls had several flat spots. The disk that holds the balls in position looks to be in good shape with no obvious wear.

soaked mentions that the driveshaft gap could be the issue. I'll check the manual to see if there's an adjustment that can be made to correct this if so. I assume the balls have to be replaced, but is the housing salvageable? Any other issues to look for?

 

[soaked]

Hi timsch,
The groove is not very deep at all, and not a problem if you shim the drive shaft to spec.
Yes replace the balls.
When the balls are touching the housing, their rotating force isn't pushing back on the fork.

This 7/16 wrench measures ~ 0.220 thick, so if it fits, its on the LOW side of the spec. (Put black tape on the handle, and keep it in gov parts, not tool box)

The gear in this pic is not clamped in the vice. The assy is hanging from the aluminum base, like the gov jig in the manual.

This site has the shims along with the balls.

The manual also shows how to shim the arms when they get too sloppy.

 

[Roger in Iowa]

Be careful when putting back together. One of the mounting bolts is shorter than the other!!!!

 

[timsch]

Much appreciation for the info, soaked. So, since the balls aren't supposed to be touching the wall if properly adjusted, I shouldn't bother smoothing out the groove.

The gap was ~0.280; no ball shop shims under the washer at all.

I assumed the internals would be worse since the gov output link rod to the carb was bent as pointed out above. I'll rebuild it, straighten the shaft, make adjustments and hope for the best.

 

[soaked]

Agree, no need to mess with the groove.
Remember to follow Rodger's advice on the bolts.( short bolt on top )

Its good you caught it before it grew too big