Small Engines (Lawn Mowers, etc.): Troybilt rototiller, seven seasons, condensers

Question
Yes Eric, the Kohler has a point and a condenser. I even tried some other condensers I have from yrs back to see if maybe the new one might be funky. And I'll give ya an update; I put the float underwater and no leaks. The machine still starts (first pull), but goes into this 'rich mode' now after a few minutes, instead of strong running for 30 minutes. I'm tempted to just try another carb, but they're kind of hard to find and I would assume they would be close to $100 complete(I'm guessing), while they are worth maybe $10 in real world dollars. What's somewhat maddening is that these machines are lying all around the country dead as a virtual endless parts nest, but nothing around here locally. If I had access to some dead machines, I could do some parts substitution like with the magneto, as I'm reluctant to try another new one.

Kevin


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Followup To
Question -
OK here is the puzzle. I have an older Troybilt ('79) rototiller with a 7hp Kohler (K161). I have used this machine professionally for seven seasons now and thought I could fix about anything on it. Trouble started two yrs ago when I had no spark whatsoever. Bought a new magneto and it fired right up and ran like a champ. However, I didn't get it fixed in time for the full season and only used it here and there no more than fifteen minutes at a time. This yr, after about a half hour of hard tilling, I get black smoke and the engine tries to stumble and die-save it by going to idle. Up until that point it runs (30 minutes) absolutely perfectly. If I do get it to power up fully, as soon as I engage it into gear it stumbles again. I've cleaned the carb in dip, blew it out, put in a rebuild kit-does the same. Tried adjusting the float so the gas level is lower-no change. Tried several spark plugs-no change (I like to do things one step at a time to discover what the real problem may be in difference to say, doing four or five ‘fixes' at a time). So then I'm starting to wonder about spark, although it starts and idles great most of the time. I have one of those fake spark plugs that you clamp to ground and I put a drill on the flywheel with a shaft attachment, spun the flywheel on ‘hi' and I get wonderful blue spark-although it seems like it misses a cycle every now and then, I'm thinking that may just be the spark tool. Talked to a mechanic here in town who works on these rototillers and he said the only thing he could think of in addition to what I've tried was that the gap between the magneto and the permanent flywheel magnet needs to be about the thickness of a business card. Well, this it tough to measure because once the flywheel is on, you can't get a feeler gauge in there (even an offset one).  So I put some putty on the surface of the magneto and spun the flywheel carefully and then took off the flywheel and looked at the putty. This is NOT scientific enough for me and although it looks like business card thickness, I can't be sure and it falls off too easily etc. He said this gap is critical because as things warm up on the motor/parts, I may be losing the right gap-too much can give me loss of power as can to little gap. Part of me wants to try another magneto and part of me feels it's the old carb, although I don't understand what changes can happen with carb in a half hr? Oh yeah, there's no way to adjust the gap unless you shim the permanent magnet or conversely, shave it. Money is really tight right now and I've already put more than I've made so far back into it (lots of rocks here to kill your tines and it's been a very cool spring for the garden crowd so far).
Answer -
Does the engine still have points and condenser?

Let me know.
Eric

Answer
Can you be near an air source when it goes into rich mode?

If so you can remove the air filter and spray air into the carb throat to see if it leans out.

Is the carburetor butterfly shaft wore?  Most of the time they are.

Another trick I've heard about is using a propane torch to find leaks in carbs/intake systems. This sounds a little dangerous to me.  DON'T light the torch, just turn it on and move it around the carb/intake.  If there is a bad leak the engine RPM is supposed to change. You might even try combining several rubber hoses together to reduce the size of the torch head to more directly control the area where the propane is directed.

Does this make sense?
Let me know.
Eric