[shaolin]

OK guys. You are all always talking about Jetting. What is it? What causes it? How do you know you need to do it? How often should you do it? How do you do it?

(84 DR250)

 

[Uncle Bob]

Jets are the hollow needles in your carburator that feed exact amounts of gaz to the cylinders. Changing the jets changes the amount of gaz that's squirted into the cylinders.

This changes your air/fuel ratio modifying the mix from lean to rich. You are always hoping to have the perfect ratio for max performance. There is a lot of debate however about what the optimum ratio is, on the other hand a very lean or very rich mixture will hurt performance.

Usually rejetting involves replacing the "jets" by small increments ( a slightly smaller or larger needle ) until the bike is responding to your liking. You would do this to resolve a factory setting that is not always set for max power or whenever you modify your exhaust. As long as it's running well and you don't change any parts there is no need to rejet.

 

[vinson16]

the only other people that jet are racers they go by humitity temperature and all sorts of stuff.

 

[Uncle Bob]

I disagree, rejetting your bike can greatly enhance performance however doing it right is another matter altogether. An experienced tech using a dyno can do wonders for your bike with proper jetting but I've seen way too many people just screw it up and kill the performance of their bikes with improper jetting.

I've also seen one guy greatly increase the responsiveness of his bike by rejetting and then try and do exactly the same jetting to a friends identical bike and never be able to get it right.