Hey all-


Can someone explain how to jet a carb? Should I just do the main jet- or change all of them (how many are there?)

I'm going to be jetting my 400ex. What tests should I preform so I know I hit the sweet spot... and should I be able to FEEL this sweet spot? I currently have a White Bro's "E" pipe, K&N air filter- air box lid removed.

Thanks for the help...

Brian

 

Since this topic is answered almost weekly, I won't take up more space on it again except to say I have written a tutorial in non-technical language with a photo of a plug in a correctly jetted engine. If you wish you can email me for it.
However, the cardinal rule in re-jetting or in making any other adjustments is to change only one thing and test before changing another.

 

Hot_shoe_cv is a trusted authority, RotGutBottom!

The whole story's a little complex for a post. Basically, the job of carburetor jets is to provide an optimum mix of air and fuel for complete combustion (about 15:1 air:fuel).

The boys at the factory try hard optimizing the carburetor, but the dang things don't work linerally--they tend to "lean out" on the top end (bottom end, too). I guess these "jet kit" guys sell slightly richer jets to weight the mixture, fuel-wise, on the top end, while the factory boys chose a compromise ratio across the operating range.

If you alter the air intake (different airbox or filter configuration, for example) or exhaust from stock, you may need re-jetting; Hot_shoe_cv's plug-reading techniques are the most reliable ways to choose jet sizes for a given engine.

If you unleash your search engine on carburetors and jetting, you'll find websites with extensive information and illustrations. MacDizzy has reprinted some classic articles in the field, for example; "How Things Work" may have something up on the subject, just to name a couple of sources.

Good question, by the way.

Tree Farmer