I had somewhat similar problem with my cb400sf. One of the carburettors was not blocking the petrol flow even after it was full + i didn't close petrol flow each time, so petrol was flowing right to the engine. As result I got too reach air\gas mixtures and carbon oxide all over the combustion chamber, spark plugs, valves and piston rings... That lead to low compression ratio.
When I was disassembling the engine one of the cylinder was filled with petrol, so I think you can try to look inside the cylinders or stick something there to check for petrol there. Btw, don't try to start the engine before you check this, it might be unsafe and cause a lot of troubles.
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Help needed :( Cylinder 1 & 2 not firing CB400SF
in Motorcycles in Thailand
Posted
I had somewhat similar problem with my cb400sf. One of the carburettors was not blocking the petrol flow even after it was full + i didn't close petrol flow each time, so petrol was flowing right to the engine. As result I got too reach air\gas mixtures and carbon oxide all over the combustion chamber, spark plugs, valves and piston rings... That lead to low compression ratio.
When I was disassembling the engine one of the cylinder was filled with petrol, so I think you can try to look inside the cylinders or stick something there to check for petrol there. Btw, don't try to start the engine before you check this, it might be unsafe and cause a lot of troubles.