300ex new piston jetting

[whplsh1]

well we got a new cylinder for my sons 300ex but here is the problem it was jetted for a .020 over 11.1 wiesco piston now it has factory bore and piston do i need to rejet it was running a little lean before i think thats why it seized up if it needs rejetting where swhould i start it has a full dg stage 3 exellerator exhaust K&N filter with lid removed it was jetted with a k&n jet kit before we got it so not sure where to start

[kd5sfq]

Originally posted by whplsh1
well we got a new cylinder for my sons 300ex but here is the problem it was jetted for a .020 over 11.1 wiesco piston now it has factory bore and piston do i need to rejet it was running a little lean before i think thats why it seized up if it needs rejetting where swhould i start it has a full dg stage 3 exellerator exhaust K&N filter with lid removed it was jetted with a k&n jet kit before we got it so not sure where to start


Jetting isn't always a function of summing up all the parts... Yes there are general guidlines but they are just guidelines... Elevation, heat, humidity, etc. all come into play... One jetting recomendation does not fit all...

This said, try installing the largest jet you have along with a new spark plug... After running it for an hour or so check the plug... Your looking for a brownish color...

If the plug white then your too lean... If it's darker then your too rich... Repeat until you find the one best for your setup... It's a trial and error thing...

For more information:

http://www.motocross.com/motoprof/moto/mcycle/carb101/carb101.html

[hardkoratvmxr]

stock is a 122 and if you have a pipe run a 125 or 128 depending on your conditions. and go from there.

[whplsh1]

yeah with the 11.1 piston it was just the slightest bit white more tan so i guess it was running a bit lean going to try this setting with the factory compression piston and go from there i wasnt sure if it was going to be a big jump or not