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CCKA motor of unknown age, origin and model/serial# mounted in 1975 646 tractor.

Here is what I have done (slowly over the past couple of months)...

Removed carb, fuel pump, intake, and heads. Cleaned and rebuilt the carb and fuel pump, decarbonized the heads/pistons, replaced eveything with new gaskets. Also replaced fuel lines and filter, removed/emptied the gas tank. (Tank filter has been gone for a while.) Reinstalled all components accordingly and she purrs like a kitten.

UNTIL, I install the air filter assembly.

It will run fine at full throttle with the air cleaner, but mid-range and idle are choppy and tend to hunt/surge. When I remove the air cleaner assembly and run it, it purrs again.

Is this a carburator adjustment or am I overlooking something? It will run like this if I remove the actual filter and leave the air cleaner assembly on. Would the steel wool type filter in the crankcase breather cause this?

Ideas/Instruction is appreciated.
 

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It may be possible that if the engine has excessive blow-by, you are giving it a massive dose of EGR by installing the air cleaner. The fact that the symptom persists without the element confirms this scenario. A second, and less dire problem is that the oil is contaminated with gas. Change the oil and see what happens.
 

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IF you have the foam "pre cleaner" surrounding the pleated element and it has excessive oil in it, it would choke your airflow.
 

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I would ck for an intake leak. When you put the air cleaner on the engine could be drawing air through a bad intake gasket or a bad mating surface or cracked intake. If it does this then the engine would run lean and cause surging. Also open up the main jet and see if it smooths out any.
 
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