I have a roadster with 2.0Ltr OHC engine with Weber double carburetor. On a ride the engine just started to spit and pop like wild from now on. The engine pushes back to cylinder 3 over the carburetor (normally it just sucks and creates vacuum). If the engine is to bring power and more fuel comes into the cylinder, there are even misfires from the carburetor… Can someone tell me what that is or could be? Is the damage expensive and can it be repaired ?