I have Jets in my Honda 400ex. I understand almost everything about the jets just need a little more info on how they work. I understand main jet controls 3/4 to WOT and the needle controls 1/4 to 3/4 and the pilot controls to 1/4. As for my question I have a high flow filter and a HMF sport series full system on my quad I think I am running a 165 main and a stock pilot jet with the needle clip on the 3rd posiontion (not sure if these are exact did the jetting last summer) what I was wondering is if not having like a 42 pilot jet is hurting my quad power wise at all because the plug is brown at WOT which means the main jet is good and I believe last I checked mid throttle is also good but I do know idleing the plug comes out black meaning its to rich. Any help on this would be great thanks

 

If the plug is black when at idle you need to turn the air screws in a bit. This will cut down on the fuel the engine sees at idle. On a non pumper carb, if you get it too lean on the air screws it will bog a bit when you get on the throttle hard off idle. The over rich condition will cover up the bog if it's a tad bit rich. If it's a pumper carb you use the acc pump to cover it up.

Bottom line is screw the air screws in until you get some pop out of the exhaust when going down hill with the throttle closed. Then turn the screw out a little until you get no pop. Your done, go have fun ridding.

 

The carb has an accelerator pump, but unfortunetly, its not adjustable.
The carb also has an anti air valve, so on high vacumn, low throttle conditions, it chops the air flow ( like a sudden hard decell condition), and most 400ex wont pop on decell, even when the pilot is too lean.
Most everyone uses at least a #40 pilot, to ease the cold starting. If you still have the #38 in there, its probably not too rich. Plug color isnt as important as drivibility symptoms. Lots of things can effect plug color, but pops, misses and hesitation are hard to argue with.
One of the best articles Ive seen writen on jetting, is this one
http://www.motorcyclecruiser.c...arburetion/index.html

And it explains the symptoms of rich and lean, and once you know that, you can adjust from there.
The mixture screw trims the pilot jet, and as long as the mixture screw is between 1 to 4 turns out, its the correct pilot jet. If it needs to be more than 4 turns out, you need a bigger pilot jet. If it needs to be in more than 1 turn out,, then the pilot jet is too big. But like I say, lots of guys run #40 or #42 pilot jets, and with your mods, Id be at least #40.

 

aight one more quick question, if my pilot jet is to small, that would effect the overall performace of the quad right?
And thanks Hondabuster I got a chance to read that article and I am going to rejet this spring, its an excellent article for people who are on the fence about jetting because they know something about it but not exactly everything, I now completly understand. Aight thanks again for any feedback guys

 

<div class="FTQUOTE"><begin quote>Originally posted by: Uberman91

aight one more quick question, if my pilot jet is to small, that would effect the overall performace of the quad right?

</end quote></div>

It would show up in low throttle ,steady speed driving, the best. If it surges, or hesitates, it could be a small jet or incorrectly set mixture screw. I usually error towards too rich, because it makes the engine run cooler in summer, and when the temps fall here in MN, I dont need to rejet, because its just about right for cold weather.
The pilot jet has effect in all ranges of throttle movement, as the end of the inlet is always in the air flow, but relativly speaking, its very minor, due to the very tiny size of the jet. This graph shows the overlap, and range of each jet.

MJ - Main Jet

JNT - Jet Needle, Tapered Section

JNS - Jet Needle, Straight Section

SJ/PS - Slow Jet & Pilot Screw

Its not that difficult to rejet, and once youve done it, you wont hesitate to do it again.