Question about Honda CB400 Four Carburettor Issues : I’m halfway through my Honda 400-4F project; the engine has gone back in the frame and is running but for some reason I can’t explain, when I rev it up, it does not come back down to idle straight away. The cables are not tight and if I prod around on top of the carbs with my finger the engine note changes. I can’t see any obvious cracks present in the rubbers, any suggestion?
Answer
Excessive mixture weakness can cause this and the fact that when you press on the carburettor tops you notice a difference in engine note does indicate that air is leaking here. I would check the gaskets underneath and screw tightness if I were you.
Otherwise it is possible that there is a problem with the carburettor linkage which will need to be investigated, probably with the airbox removed so you can check the free movement of the slides.