jetting question kinda

[phildogg]

ok I have an 04 400 ex with no airbox lid,k&nfilter,and a hmf slip-on. I'm running keihin jets. I currently run a 155 main jet with no probs I'm at 1200ft above sea level. my question is why do I see people with 165-170 mj with about the same mods as me. this seems as it would be way over rich to me. On the hmf website they ran a 152 mj with a full exhaust and no lid. I was just curious why people run that big of jets. thanx in advance.
phil

[wilkin250r]

I don't know about each and every individual person, but I know that many people start with a ridiculously huge jet, and work their way down until it runs decent.

It might be richer than needed, but certainly not lean, and therefore it's safe.

[phildogg]

well that is what I was thinking but I have thought of bumping mine to a 158 for winter but no higher. like to get as much as possible out of it.lol
phil

[tater_kamik]

i think a lot of people just throw a large one in there to be safe, it works, then they dont worry about it. im running with an 160/165 at 400ft with a built 686, and there are guys running the normal exhaust and filter with the same jets or bigger...

[phildogg]

yeah I kinda figured that myself but thought I would ask. thanx alot bros.
phil

[howshnazy]

phildogg could you please tell me what pilot jet size you run, i have the same set up and need to find the correct pilot jet size.

[phildogg]

I'm running the 42 keihin pilot.
phil

[Pappy]

I think it all starts with the exhaust company. A person orders a new pipe and it arrives with a main jet that ensures the buyer will not grenade his engine due to a lean out condition.

Since most first time pipe buyers have no clue what is the proper jetting for them (neither does the exhaust company) the trial and error process begins.

Some quads, especially todays high performance atv's, are very picky about jetting. The 450R runs a 118 main stock, add a pipe and you can keep the jetting as long as the airbox is closed. Open the airbox and you will jump to atleast a 170!

The 400ex has to go down in history as the most over jetted quad. Most of the time, just watching a person struggle to get thier 400 started and idling is as good as a magic show. Pump 3 times, start, let sit until it dies, repeat.

Thanks to the internet, one can now get more information to get pointed in the right direction, lets just hope they use it!

[eldercyclerep]

i have a Yoshi Full Exhuast K&N Powerlid and filter and i run a 178 main