Manifold (intake and exhaust)

The intake manifold connects the carburettor or throttle body to the cylinder head. On many bikes it is a short rubber boot; on multi-cylinder engines it may join several runners. The exhaust manifold (headers, downpipes) collects exhaust gases from the ports and leads them to the silencer.

Cracked intake rubbers let in unmetered air, causing lean running, erratic idle, popping and hot running. Spray a little carb cleaner around the joints with the engine idling: a change in revs reveals the leak.

Exhaust manifold leaks show as ticking at the port, black soot marks and popping on the overrun. Always fit new exhaust gaskets when refitting headers and tighten the nuts evenly.