FOG's Airbox Mod

(Relavant Thread: https://www.ex-500.com/threads/fogs-air-box-mod.3342/#post-37431)

The stock EX jetting from the factory setting is extremely lean at Idle and low speed running. Then overly rich at high RPMs. This is due to the ridiculous EPA requirements and the rules for testing. The EPA test concentrate on the low end of the performance. So to get something approaching a reasonable overall performance the over rich high end jetting takes over a little sooner in the RPM range ,then reasoning that not many run full throttle for very long ,or couldn't tell the difference that a fat jetting up high makes.

The FOG Air box mod addresses this. By enriching the bottom and leaning out the top.

I have discovered a minor alteration (MOD) to the airbox that has proven value. In my never ending quest for an unfair advantage for my race bike. I was testing jetting on a Dyno one day. I discovered that the Air box was too restrictive and ran a vacuum that seemed too high. I made many tests to determine that 1 additional hole of 1" in diameter was Ideal. This hole is located in the rear facing end face of the left side airbox cover. Further tuning proved that adjustment of the Pilot screws was all the Jetting that was required. Now I also used a KN filter, because I got 1 hour of free dyno time with the purchase. My net result was: 53.9 HP or a improvement of almost 4 HP from stock (My stock was not necessarily optimum)..

OK here it is again:

Drill a 1 inch dia hole or multiple holes with a area of no more than .7854 square inches. Remember pi X R squared. In the rear end of the left side airbox cover. This location was chose to Hide the mod from prying eyes in the pits. I tested no other

Fit a new KN filter

Be sure your carb. Pilot jets are clear and the Sync. is good.

Then un plug the pilot screws and adjust them for the best results. I did it this way: Wack the throttle wide open and listen to the engine rev to about 8-9000 RPM adjust the pilot evenly about 1/4 turn each time till the smoothest acceleration is obtained.

Reset Idle to taste.

No you can not substitute any thing else for this MOD. You of course can do anything you want. just don't call it the FOG Mod.

The Factory has not adopted this mod in any way, regardless of how many holes or trumpets you count it has not been done, unless you have put a 1" hole in the end of the left side cover. it needs one.

Please do not add or attempt to alter this post, write your own.

Thanks FOG

I have to add this disclaimer: It is assumed your engine is in otherwise perfect condition. The FOG MOD is the last tuning you do. after valves ignition wires etc.

FOG