21HP Briggs-Stratton runs hard under load.

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  #1  
Old 05-04-10, 10:34 AM
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21HP Briggs-Stratton runs hard under load.

I have a Husqvarna rider with an ESL656 Briggs/Stratton, 21HP with about 145 hours on it (according to the meter). I put it in service not to long ago and came up with some interesting symptoms.

It started when I engaged the blades- Rough running, low rpm's and black smoke.

A fella cleaned out the the carb for me and said that it was really very clean and then he messed with some and found this.

The mower will run up to full speed with no load and does pretty well in full speed just riding around. The blade engagement is the load that upsets the mower. I can use the mower in about 3/4 throttle with no problems. The work-around is to engage the blades at a lower throttle position and then increase the speed until the engine complains.

He now wants me to consider coils or voltage regulator. I'm thinking governor. I've even found articles talking about kill circuit diodes.

Otherwise, plugs look good, all the blades turn with no binding, new gas, air filter is good, and etc.

I'll be tweaking on it until I hear from the gurus.
 
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Old 05-04-10, 11:46 AM
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That kill switch diode thing is interesting. I ran the engine up to full speed in neutral with the brake off. Running great while I sat there. I lifted my weight off the seat and sat back down before the engine cut off. Black smoke and rough. Hmmm.
 
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Old 05-04-10, 07:11 PM
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Originally Posted by Morania View Post
That kill switch diode thing is interesting. I ran the engine up to full speed in neutral with the brake off. Running great while I sat there. I lifted my weight off the seat and sat back down before the engine cut off. Black smoke and rough. Hmmm.
that seat switch works in series with a switch on the pto. Maybe you have a short somewhere in that circuit that is causing the engine to lose spark as it thinks those 2 switch are closed. Any grounding in circuit after the pto switch to the seat switch would cause that. I get it sometime just by bouncing in the seat or shifting too far one way.
 
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Old 05-04-10, 07:58 PM
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I haven't had a chance to try this yet but the test for these problems is to disconnect the kill wire from each coil. They say that I have found my problem if the mower runs normally after that.

I don't mind disabling the kill circuits but I want to keep the one that kills the engine when the blades are spinning.
 
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Old 05-04-10, 10:39 PM
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Don't disable anything, just try taking the kill wires off the coils to see if that's even the problem at all. I doubt it, it sounds like valves out of adjustment, maybe even a camshaft going bad.
 
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