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Discussion Starter #1
I've got a 1986 Case 446 with an Onan B43M engine and a Nikki carb. I took the carb apart this spring, cleaned it (looked brand new, the tractor only has 225 hrs), and put it back together, along with new points/condensor (thanks bhildert) and it ran great.

Recently, it's began to hunt at idle (governor speeds engine up then back to idle repeatedly) and I think it's due to a vacum leak on the split manifold.
Reason I think it's a vacum leak is because if I close the choke almost all the way, it idles normally, dead smooth. If I put it at high idle (full throttle) with no load it almost runs perfectly steady, the RPM's waiver ever so slightly (most probably wouldn't notice but I do) and when you load it (tilling, grass cutting, etc) at high idle it runs perfect.

Has anyone else had this problem?
 

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If you suspect it has a vacuum leak, take an unlit propane torch and carefully direct the propane gas at the intake split-line, carburetor base, ect. The engine will speed up if it has a leak.

:fing32:
 

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If this was a Kohler engine...I would say to check the throttle shaft for looseness.
Put a bushing in mine to tighten it up and solve an air leak.
 

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Discussion Starter #4
What kind of carb on the Kohler? Mine has a Nikki, seemed pretty tight when I took it apart (again, it only has 225 or so hrs on it).
I'll start at the intake and report back
 

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Was there ever a resolution to this? I'm curious because my exact tractor is doing similar things.

To add to mine, it will eventually sputter out and on one occasion you could hear fuel boiling in the carb. On all occasions the tractor won't start again until it sits for a while.
My carb was completely rebuilt professionally 3 months ago. This problem is new this week.
 
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