justting help ( i know this has been asked a million times.)

[exrider008]

i am doing a 406 with a HMF full system and k&n filter. what should i do for jetting?
thanks!

[nosliw]

start with a 155 keihin hexhead main, 42 pilot jet, and needle clipon the second position from bottom

[exrider008]

Originally posted by nosliw
start with a 155 keihin hexhead main, 42 pilot jet, and needle clipon the second position from bottom

thanks alot! anyone eals i just want to see what other people think.

[GPracer2500]

The key word in nosliw's reply is start. There is no magic spec sheet that has jetting specs for each settup. There's just too many atmospheric and mechanical variables at play. Starting points are good, but don't expect them to be exactly right. I've been surprised how far away from a "starting point" I ended up.

In my experiece, jetting is a process--mostly trial and error. Basically: Find a starting point then make one change at a time. Test ride between changes and look for performance characteristics at different throttle postitions. Keep going richer or leaner until performance stops improving. That's the jist of it.

Remember that the different carb circuits relate to different throttle postions. You'll go in circles trying to evaluate your jetting without understanding when each of the various carb circuits are active. For example, don't try and tune out a 1/3 to 2/3 throttle stumble with the main jet. Understanding those fundamentals will make the whole process faster and more sensical.

If you really want to get a step-up on your jetting skills, take an afternoon and just start making jetting changes. Remember, one change at a time. Eventually it will become clear what rich feels/sounds/rides like and what lean feels/sounds/rides like. And also, where on the throttle postion those conditions are occuring at. It's much faster/easier to FEEL and HEAR how a rich main or lean needle behaves than to try and correlate what you read with what is happening with the bike. Said another way, if you purposely set up rich and lean conditions you can teach yourself how to recognize those conditions--even when they are minor.

my $0.02

[exrider008]

ok thanks alot i gess i will have to play with it.

[cals400ex]

air box lid on or off? i usually start a little higher than the 155. i rather be a hair richer for the break-in than a hair lean. but temperature, porting, altitude, humidity, etc. all make a difference

[SlolY BlazN]

all this is true ...155 umm no go w/ 160 richer better to start