noob question: what is jetting?


8 replies to this topic
  • dcecar

Posted May 13, 2008 - 01:36 AM

#1

I am a total noob, just got my bike 3 days ago. I've read alot of posts about overheating, smoke etc, people mention jetting, I have no idea what it is.

Can anyone explain what it is, what it does, what adjustments make what effect etc. thanks -Dejan

  • jdtriplett

Posted May 13, 2008 - 02:07 AM

#2

Hi,

The JET in Jetting refers to the a metering device in your carburetor that restricts the fuel rate as it is processed for combustion. This sets the ratio of fuel and air so that the proper explosion can take place and give the maximum power the engine can provide. jetting usually refers to changing or adjusting this metering rate to improve your power based on ambient conditions mostly.:thumbsup:

L@ter Bud

JD

  • KJ790

Posted May 13, 2008 - 03:38 AM

#3

For an engine to run properly it needs the right ratio of fuel and air mixed together. Your carburetor does the job of allowing fuel to mix with the air as air goes through it. The jets are like small little pipes that allow the fuel to flow through before mixing with the air. Basically, the smaller the jet, the less fuel goes through it to mix with air. As temperature, humidity, and elevation change, the properties of air change and thus the amount of fuel needed to make the right ratio changes. For this reason you need to change your jets accordingly for different seasons and elevation. There is a range that the jets can cover so you don't need to change them for a one degree temperature change, but you should change them for a 15-20 degree change or you can damage your engine.

  • sirthumpalot

Posted May 13, 2008 - 06:21 PM

#4

4 strokes aren't as easily damaged by incorrect jetting as 2-strokes are. If the jetting is off enough to cause damage then it's most likely going to be running pretty bad. In general, if your stock bike is running good then the jetting is fine. These things are actually pretty flexible and if you're near sea level and don't get extreme hot or cold then it will probably run just fine year round without any jetting changes at all. For example I'm in S FL and I ride a 426 and I've ridden as hot as 95+ and as cold as 50 and it runs fine with stock jetting, maybe a little fiddling with the fuel screw. Jetting changes would surely bring improvements, but not enough to justify the effort to make changes in my personal opinion.

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  • dcecar

Posted May 13, 2008 - 06:30 PM

#5

thanks. sounds like i dont have to mess with it much at this point

  • Sonic99

Posted May 14, 2008 - 06:10 AM

#6

Can someone post post up a pic of the fuel idle screw on a 426???

  • grayracer513

Posted May 14, 2008 - 11:08 AM

#7

Here is the stock fuel screw, viewed from under the carb:

Posted Image

Here is the location of the screw with the carb in place. (red knob is an aftermarket screw):

Posted Image

  • Berm-Saw

Posted May 14, 2008 - 01:17 PM

#8

Here is the stock fuel screw, viewed from under the carb:

Posted Image

Here is the location of the screw with the carb in place. (red knob is an aftermarket screw):

Posted Image


where does the fuel screw change the mixture at,..........at idle?.....where at in the throttle location:excuseme:

  • grayracer513

Posted May 14, 2008 - 02:42 PM

#9

where does the fuel screw change the mixture at,..........at idle?.....where at in the throttle location:excuseme:

Only at idle and in the first 1/8 throttle as the carb transitions to the main circuit.





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