I just picked up my 00 Honda 400EX tues.. I F-ing love this thing. got a :smokin: deal on it too !! but anyway.. i'm not sure what gas to run in it.. Is premium recommended ?? i read the race gas thread so i wont waste my money on that.. but te guy i bought it off of said it HAD a big bore kit and is back to a 400 now.. so i THINK the engine is stock.. i did put a lil hotter plug in it the old one fouled.. i think it may be jetted for the big bore still ?? i know very little about quads but am learning rather quick..

I have a 450R and run either premium or mid grade, they don't use alot so it not like its alot more money. in my 4wd quad I run the cheap stuff.

premium is what i run (450R) just right for stock compression

Your jetting isn't really to effected by bore size,,the main thing that effects jetting is air in and air out ie; airbox lids and exhaust

Its better to be a little fat than lean

Well it' runnin good starts good each time. no more stahling so the hotter plug solved the problem.. i think ill run premium in it.. it's only a couple gallons so the $.20 difference wont kill me.. now i just gota keep the old man from dumping my quad gas in the lawnmower lol

I have an '01 (piped, jetted and K&N) and my manual says to run premium in it.

So I do.

Run the premium fuel. The air cooled motor gets a littl hot at times, so better safe than sorry. You can go up to 10.5:1 comp easily running premiun fuel.

The factory keeps the compression rather low to keep everyone safe no matter what fuel they use in the quad. However, as everyone else has said, I would suggest just sticking with premium to eliminate the possibility of problems.

FWIW, 400s are ok quads when stock but will wake up nicely when you increase the compression and add a cam. There really isn't too much that needs to be done with the head unless you want to cut bigger valves in it as the heads are hard to improve on.

Just run 110 lol jk just put in 91 you be find