Tell me I'm thinking wrong...please!

Bret4207 · Jun 29, 2019

My ancient Bobcat 444 was repowered with a 23hp Briggs Vanguard. It's worked good so far, maybe 30 hours actual run time since 2012. Suddenly it doesn't want to start. Tried new plugs, NGK's, and it started right up and ran. Used it for maybe 5 minutes and it stalled. Now I'm having same problem as before I changed plugs- it wants to flood and foul the plugs and I get a small backfire through carb from time to time. I'm thinking I somehow sheared the flywheel key, which means removing engine from the skid steer- not fun at all. The other possibility is that it's a wiring issue. Some ice broke a couple wires 2 winters back. I repaired them and it's run good since then, but I suppose it could be a bad connection (crimp style) but that doesn't seem to make sense since it ran good before. I've check the valves and they seem to be opening and closing alright, no crud in the heads, good compression, etc.

I'm out of ideas outside of the key being sheared or maybe a bad ignition altogether. ???

Bob · Jun 29, 2019

Disconnect the ignition "kill" wire at the engine to rule out shorted wiring between the engine and the switch, or a bad switch.

(Don't EVER feed battery voltage into any of the "kill" wiring!)

If that doesn't help, the two coils are actually each a complete E.I., and are connected to the common "kill" terminal each through a wire with a diode.

If something happens to that wiring (mice?), or one or both of the diodes, strange things can happen.

Unfortunately, the flywheel cowling hides all that from view.

jeffcat · Jun 29, 2019

Part of your description sounds like carb problems. Hope I am not all wet but
have seen some goffy things on my Briggs twins. Those engines have a problem
with that NIKI Carb and it is due to the ethanol. They are actually two
carburators in one body and they interact with each other.There is a little
gasket inside that has four little bitty holes in it. The bottom two swell up
and throw the whole carb out of balance. Also the two brass jets have very
small "O" rings that disintegrate and cause their own sort of problems. If the
key is partially sheared the engine will run VERY hot. Like trying to melt your
muffler. That wrinkled washer "William's washer" on top of the flywheel looses
its tension after a while and the flywheel can move. I have recommended to
several people to buy the replacement carb and they are so cheep but work soooo
good! Give one a try. Just make sure you follow the diagrams. That gasket with
the little lips on it must be installed correctly. Everything just screws on.
Maybe 20 minute job.

jeffcat · Jun 29, 2019

My advice goes hand in hand with Bobs and most likely to go over if you pull the engine. It is always fun trying to diagnose over the internet. Fouling, running hot, etc. again sounds like carb. When you pull the engine, "sorry" take the bottom of the carb off I bet ya it is full of crap.

37chief · Jun 29, 2019

I would check the flywheel key, as someone else mentioned. Condensers will give a problem also. Stan

Olliejunkie · Jun 29, 2019

I have one that was covered to propane. Fouls one plug within hours of using.

Texasmark1 · Jun 30, 2019

I've had Woodruff keys partially shear and knock the timing off enough to not start....seems amazing but replacing the key solved the problem.

However, to damage a key an impact of some kind had to happen to the crankshaft with the engine at high RPMs. If you didn't have such impact since
running strong, I'd look elsewhere.

Bret4207 · Jun 30, 2019

Thanks to everyone! I guess I'm going to be pulling it one way or the other.

Tell me I'm thinking wrong...please!

Bret4207

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Bob

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jeffcat

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jeffcat

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37chief

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Olliejunkie

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Texasmark1

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Bret4207

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