Cub won,t fire on #4

Anonymous-0 · May 7, 2012

I have a 47 Cub that was running fine until head gasket blew. After new gasket , won,t fire on #4. Compression around 100 psi on all four cylinders, when plug laid on block shows good blue spark, starts instantly and runs on 3 cylinders. plug seems not as wet as it should be. Swiched plugs around, Disassembled and cleaned carb,seems like not drawing fuel to this cylinder, but good compression. any ideas?

old · May 7, 2012

Sounds like the intake valve may not be opening like it should or maybe even the exhaust valve or both

Bill in NJ · May 7, 2012

Definitely sounds like a valve problem. Maybe burnt valve and/or seat, bent push rod or broken spring.

teddy52food · May 7, 2012

With 100 psi on all 4 cylinders????? Check for a leaking intake manifold. Check for carbon tracking or anti-freeze in the dist cap.

Janicholson · May 7, 2012

Put a teaspoon of gasoline in the #4 hole. Put the plug back in and start it. If it runs on 4 for a few strokes, it is probably a vacuum leak at the head to manifold gasket. (you didn't leave a rag in the port?) If it does not run with fuel, I would suspect a non operating exhaut valve. I would also change the plug wires from one to the next just for a test. Jim

mkirsch · May 8, 2012

He says he's got spark on #4.

Cub won,t fire on #4

Anonymous-0

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old

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Bill in NJ

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teddy52food

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Janicholson

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mkirsch

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