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Small engine problems?

J

Josh in Pa

Member
I have a 20 hp b&s vanguard on my mower. Lost power, missed real bad and blew black smoke. Also backfired through the carb some. Pulling one plug wire makes no difference, but the other kills it instantly. Cylinder that is not firing has 150 lbs compression, both valves move. Tried two coils and disconnected the kill wire from both coils. No luck. Started it up, it seems like it is getting oil inside the air cleaner, and with a valve cover off to check that valves were opening, seems like a lot of pressure in the crankcase. Any ideas where to go next?
Josh
 
Backfiring through the carb usually means the intake isn't closing or burnt intake valve. Check intake clearance. better check all valve clearances. The exhaust is as important too.

Is there a spark on the bad cylinder? Just because you changed coil, doesn't mean you didn't put a bad coil on or you have a bad plug.
 
My 14hp BS vanguard did that too, oil in the carb was an indication that the crankcase is loosing its vacuum to keep the oil in the engine so it sucks it thru the PVC valve to the carb. My crankshaft seal was bad at the output end of the crankshaft. This allowed atmospheric pressure in to the crankcase and let it suck the oil up to the carb and flooded the air filter. I removed the electric clutch and bad seal. Installed a new seal and the electric clutch and it ran perfectly. My friend that is a small engine business owner told me this.
 
Sounds like you blowed a head gasket. Briggs are known for this, it causes a lot of crankcase pressure when it happens.
 
If you had a burnt or leaky valve or blown head gasket you wouldn't have 150lbs of compression.
 
does yours have over head valves, if so check valve pushrods and rocker arms they pron to brake rocker arms or bend push rods from being run with to much lash
 
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