"frank1492" wrote in message
...
This engine is on an Ariens Emperor of 60's vintage. The mower was
purchased used in the 70's and has given good service. This problem
has become worse recently.
The engine starts extremely well and rarely if ever dies, but it
runs unevenly. When it falters, it emits a puff of black smoke. The
plug is black and occasionally sooty. The plug and air filter are
brand new. The carburetor was today completely disassembled and
found to be very clean. Upon reassembly, the condition seems
exactly the same.
Needle valve adjustment does not correct the problem, but
does affect engine operation as one might expect.
It appears the engine is running too rich when it falters.
Can someone give me a list of things to look for? Some
things I wonder about:
Leaky head gasket
Badly burned points
Bad rings (not likely because smoke is not white and no white
caking on plug.)
Improperly seating valves
A possible clue: When the mower travels uphill and is therefore
under extra load, there is generally a series of smoke puffs.
Help much appreciated!
Frank

I'm suspecting something to do with the float - especially when you mention
the uphill difference. Is there a screen in the inlet ? If so I'd blast it.
It's hard to tell how "clean" carb parts are by sight. I'd clean the float
needle. It's hard to imagine how the float setting could have changed so I
would guess that's OK unless the float has a pinhole and it taking on a bit
of fuel.