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Main jets for motorbike carburetors (made by Dynojet - USA)
DJ main jet
CJ main jet
YJ main jet
Available in 4 versions and different sizes for Mikuni and Keihin carburetors for 4 stroke engines.
To achieve good carburetion, it is advisable to start from a plausible basic step.
In doubtful cases, it is better to start with rich mixture rather than a lean mixture.
Generally speaking, if the engine is supplied with a mixture which is too rich, it will tend to flood or surge.
Conversely, if the engine stumbles or misses, the mixture is too lean, while in certain extreme cases knocking can occur.
Backfiring during coastdown is a sign that the mixture is leaning out, that air is getting into the exhaust system, or that the idle mixture is too lean.
At wide throttle openings, however, the mixture may be correctly adjusted or even rich.
The inside of the tailpipe can provide useful information about fuel metering.
This information, however, depends on how the motorcycle is used.
Black deposits on the inside of the tailpipe, for instance, can indicate that the engine is often idled for a while before being shut off, though the mixture may be lean at WOT.
The best thing to do, in any case, is to proceed with caution and avoid overly lean mixtures: it's better to err on the rich side.