Engine dies when mower deck is turned on

Husky rider w/20hp Kohler Magnum (1995ish). Spec #57528.
For a long time it ran rough. Surges a lot. Throttles up slowly. Blows black smoke when throttling up. I'm told this is carb problem.
The other day I'm mowing and its running rough and surging. When the rpm's are on the way up it blows black smoke. But after a while it starts to stall out. I shut off mowers and it gradually gains rpm's. Mowers on...dies. Mowers off...slow recovery. I drove back to the house and it died. Wouldn't restart.
Checked spark. None sometimes or very weak. Found that the spark plug wire connector is rusted and starting to crumble. Ah hah! Could the slow deterioration of the connection cause a bad spark which caused the rough running and black smoking? Soooo, I replaced spark plug ends. It started up. Ran rough. Sooo, I took the carb off and tore it apart and soaked it in cleaner. Reassembled. Started immediatelly. Still gains rpm's slowly. Turned mowers on. Engine immediately dies just like if the key is turned off. Turn the mowers off and engine gains back it rpm's.
Any ideas? I'm stumped.
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It sounds like its worn out , start with a compression test , how many hours on it
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How old is this mower -- does it have ignition points or modern transistor ignition. It sounds exactly like my 30 year old Troy-bilt tiller. If I didn't engage the tiller tines carefully it would stall or would only slowly build up revs. The points were dirty and needed replacing. Followed my manual exactly in regard to installing the points and how to re-time the engine while replacing the points which required removing the head. While it was open, I scraped carbon off the piston and the inside of the head. Put it all back together and fired it up. The old engine fired up immediately and had its old power back like a new engine. This was a 30 year old Tecumseh.

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Black smoke is a fuel issue, running too rich,
While smoke, in an air cooled engine as you have, would be oil.
Either issue can, and will foul the plug.
Putting a new one in, will prob get it to start, but will NOT fix the underlying issue of a carb problem.

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I adjusted carb as well as I could. Still slow on building RPM's. However, it starts immediately and runs better then before. I did have to adjust the float. I think it was filling with too much gas. This might has caused the rich mixture. I think I lowered the float level about 1/32 or 2/32 inch.
As for the mower problem...I took the drive belt off and started it up. As soon as I turn the mower switch (electric clutch) on the engine putters down till it shuts off. Seems to be identical to turning off the ignition switch, and also identical to what it does with the mower drive belt attached.
I'm thinking electrical short. What caused it I can't imagine. But how do I tell if I'm losing ignition when the mower is engaged? Or, what else should I look at for a clue.

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I had a similar problem on an old B & S engine wher ethe plastic vane used as part of a governour assembly had broken.
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This is an addition to a reply that I posted a few minutes ago.
I just started the engine with a spark tester attached from the plug wire to the plug. When running the spark looks very weak and when I trun on the mower switch the spark disappears and the engine dies. Hmmmmm. What does this point to?

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snipped-for-privacy@blclinks.net (Daryl Helwig) wrote:

deck without the seat interlock engaged it will kill the engine. I really suspect that you have an electrical problem in addition to any fuel problems.
--
Jim Rusling
Partially Retired
  Click to see the full signature.
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The engine ignition system should be completely separate from any generator system they'd use to power the electric clutch. Most small engines use a magneto ignition system that relies on magnets in the flywheel to move past a coil to generate the spark voltage. Sometimes they will add a large coil of wire around the flywheel and let the same magnets generate auxiliary power to charge a battery or run headlights and the like.
If you have a voltmeter available, can you put it across the battery and check the voltage with the engine running at a high idle, so it's charging the battery. You should get 13-15 volts DC there. Then engage the clutch and see what happens. If all is well, the voltage should remain there. If not, then it's time to do more snooping.
Bob

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My best guess about the engine dying when you engage the blade is a bad safety circuit. The last three riding mowers I have had required the operator to be in the seat when engaging the blades. You may have a bad switch, wire or connection. The switch is probably under the seat or is actuated by a lever or linkage connected to the seat. . As for the slow acceleration, that sounds like a carburetor or governor malfunction.

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It was the switch under the seat. Yesterday when I was riding it and turned the mowers on it died, just as it did the other day. A friend mentioned the seat switch and I mentioned that I was on it when it died. But I went out and tried it again anyway. Guess what. It works fine. I assume that the switch is going bad and intermittently doesn't make contact. Maybe its rusty like the plug wire connections were.

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