What main jet should i run on a 300EX with only a supertrapp no other modification? I live about 300 feet above sea level in North Carolina. Stock is a 122 according to my local dealer, any help would be thankful.

 

You probably won't have to rejet at all. If you don't add an aftermarket air filter there should be no reason to increase jet size since you haven't increased airflow. Airflow and jet sizing work hand in hand. To really see any benefit from a pipe you need to increase airflow into the motor. More flow in, more flow out = more power. If you decide to do the filter and pipe together buy the next two jets: 125 & 128. My stock jet was a 122 and with a pipe/filter I went up to a 125. Hope this helps.

 

Where Throop, PA?

 

It's near Scranton/WilkesBarre.

 

When you said "SuperTrapp", you didn't specify whetheryou meant the pipe & silencer or just the silencer. I run a Curtis Sparks Racing pipe with an outside disc silencer (?) behind it. Sparks recommended two sizes fatter on the main as a starting place. After test riding & plug reading, it would tell you whether it's necessary to go up or down. As it turned out, with the filter upgrade, I had to go three sizes fatter on my main for my Warrior to run right at 3200' elev.
If you only added the silencer, the other post is probably more appropriate info. I would still do a high speed test and plug read to be sure you're not lean.
Oh BTW, the reason for the (?) after the word "silencer" above is because with 20 discs it is LOUD!

 

I got the complete kit supertrapp EAR and header, ill read the plug and see if i need to rejet.

thanks