www.zxrworld.co.uk

Is it actually worth dynojetting my 400, it has a different exhaust system and filter but cant the standard jets just be tweaked to get the thing running spot on, as it seems everyone has to have dynojets who own a zxr 400? Are there some massive differences in the design of the jets or are they just different sizes?

You dont need a dynojet kit, but a dyno session to match the jets to your bike. The standard jets are perfectly matched to the zxr400 airbox and exhaust combination, but Once the induction and / or exhaust system are changed, the standard jets are almost certainly no longer suitable.

The optimum air / fuel ratio is around 13 to 1, so if you have a less restrictive airbox, and a free flowing ( louder) exhaust, the mixture will contain more air, but (unless you change the jets) become too lean, air fuel might move to wards 14 to 1.

A lean mixture can cause pinking ( per detonation) which leads to a holed piston.Typically, a zxr will also have a flat spot and run lean between 7 - 10 thousand revs if jetted too lean.

The dyno will measure the air fuel ratio across the rev range, and by changing the jets ( takes less than 10 minutes) can achieve the optimum air fuel ratio (mixture). The wonderful by product of this is a much crisper throttle response and more power, which is why engine development is done using a dyno.