Briggs and Stratton stalling under load


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Old 02-21-17, 09:01 AM
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Briggs and Stratton stalling under load

Thanks for your help in advance. I just found this site and need some advice, I'm stuck on what to do next.

Here's the setup:
23HP Briggs and Stratton Model 386447-0121-E1, made in 2006, on a mud buddy surface drive boat setup.

The engine runs fine when not under load, but bogs down and stalls when under load. When I run WOT with no load, the engine also cuts out when powering down to idle.

Here's what I've done so far:

-Replaced plugs and coils
-Replaced fuel filter and fuel pump
-Replaced air filter
-Replaced oil filter and changed oil
-Replaced carb


Initially the engine was just running on one cylinder, and it would run fine under load just not with much power. I replaced the coil packs, which fixed the one cylinder problem, but now won't run under load. The engine also started dieseling for 5 seconds or so when I replaced the coil packs.

I then removed the carb to clean, but the mixture screws were broken and I couldn't remove, so I figured it was better to just replace the whole thing. I really thought that was the answer, but apparently not. I haven't done a compression test, but based on how hard it is to pull the cord I think there is good compression.

I'm sorry my first post is this garbage, but looking forward to getting this fixed!
 
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Old 02-21-17, 09:14 AM
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Sounds like a governor issue.

My snow blower was doing similar this winter. Found the linkage was binding so did a carb and governor linkage clean up and ran like a champ.
 
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Old 02-21-17, 10:24 AM
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That may be a diode problem in the kill circuit. That would lead to cross firing. You can go to the kill wire coming off each coil and trace it to the first juncture and disconnect the kill. If it runs good then the diode is probably bad.

With the kill disconnected you will have to choke it to kill it, so keep that in mind while you're testing.
 
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Old 02-21-17, 11:23 AM
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I was thinking the same thing as marbobj.
 
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Old 02-21-17, 01:14 PM
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Thanks for the replies. Would the engine start if the kill circuit was bad? I'm not that familiar with the wiring on it, but could you explain how the kill circuit would be related to putting the engine under load?
 
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Old 02-21-17, 01:52 PM
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It would start and run with performance issues. The diode in the kill circuit keeps one coil from grounding through the other coil via the kill circuit. This lets you kill the engine with one switch rather than a separate kill for each coil.

Making a long story short, a bad diode would mess up the ignition of the engine.
 
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Old 02-22-17, 06:42 AM
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Marbobj is correct if each of the two coils have their primary connected to a single pole kill switch and the one electrical isolating diode shorted. If the diode opened, the kill switch, when operated, would not stop the engine from running on one cylinder. Additionally,you would have to ground the diode (side closest to the coil) or apply the choke to stop the engine.
IMHO this is a poor design unless both pistons reach top dead center at the same time. I would remove the diode and replace the factory kill switch with a 2 pole push button switch ( common and normally open terminals). Wire each coil primary to a separate pole ( normally open contact) and ground to the common of each pole. This maintains electrical isolation between cylinder coils unless stopping engine.
 
 

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