Because the consequence of too tight valve gaps can be serious, it is sometimes said that a ‘noisy tappet is a happy tappet’ (the noise – from the hammering parts – is a sign the tappet is not too tight). But as we have seen, it is not quite that simple. When specifying the clearance … Read more Honda C90 – correct valve clearance
Once you have the engine back together an important job is to adjust the valve clearance (sometimes called “valve lash” or “tappet gap”). The clearance you are adjusting is the gap between the “tappet” and the tip of the valve. Tappet is an Engineering term meaning: “a moving part in a machine which transmits motion … Read more Honda C90 – valve clearance
The valves are held in place by metal guides installed in the cylinder head and on some C90s (including the c90 z2) there is a small synthetic rubber seal on top of exhaust valve guide. This can be seen below (note that Honda use the term ‘stem seal’ rather than ‘valve seal’ in the CT90 … Read more Honda C90 – valve seals
Before you remove the valves you have to take off the tappet covers. A common problem is that these covers seize tight in the cylinder head and – since they are made of a soft aluminium alloy – they can easily be damaged during removal. It is easier to remove them when the engine is installed in … Read more Honda C90 – valve removal, cleaning and lapping
Here are a few posts on the topic of valve timing and valve adjustment. Happily, since the c90 is such a simple engine, it is a good place to learn about these fundamental automotive terms. Here goes! The c90 has one cylinder and it has two valves: an exhaust valve and an intake valve. The … Read more Honda C90 – valve timing
Looking at the CMSL microfiche parts diagrams, the older Kowa tool kits – for example the c100 from the 1960s – contained: an open ended 10/14mm spanner 17mm and 23mm ring spanners a set of pliers Pliers a spark plug socket a screwdriver handle with one slotted and two cross head bits. The kit also included tools … Read more Honda C90 – tool kits
Kowa Seiki have made tools for Honda since 1956, initially making their special workshop tools and then going on to make the tool kits for all their bikes from the 60s until the early 2000s. From the 1970s they also made tools for the Japanese government, Mazda, Kawasaki, Suzuki, Yamaha and Mitsubishi. Add all that … Read more Kowa tools
There are only a handful of things that can go wrong with the simple carburettors used on the Honda c90 and – once you have a rough idea of how they work – the fixes are straight forward and largely common sense. Blockages The tiny holes in the emulsion tubes and jets can get blocked … Read more Honda C90 – carb – cleaning and replacement parts
When the engine is cold fuel tends to condense on the walls of the intake manifold and cylinder and this make the engine hard to start. The solution is to make the mixture richer, either by temporarily adding more fuel or by restricting the amount of air. The mechanism used on this carburettor is a … Read more Honda C90 – carb choke
The idle (or “pilot”) circuit controls the mixture of fuel and air at low throttle speeds. Here are the bits involved in the pilot circuit 1)it is common to use the term “idle circuit” in the UK but we’ll stick to “pilot” from now on, as that is what Honda uses in their documentation : … Read more Honda C90 – carb idle circuit