i just recently added a a powercore 4 slip on with uni filter on my 400ex and my spark plug is white what is the problem i didn't jet it im running the stock 146 jet

 

Your problem is you didn't rejet, your running HOT. This can and will cause damage to your motor. You need to go to a bigger jet then a 146 jet, and keep looking at the plug to see the color and how it performs. Brown is the ideal color. Try bumping it up a couple sizes and look at the plug, if it's black your still too rich, if brown...you've got it..if white you know it's too lean, go bigger.

 

I agree. Don't forget the pilot screw. You may need to drill out a brass plug to access it. You shouldn't need a new pilot jet with just exhaust and filter, you should just need to richen it up a little. This controls air/fuel mixture at idle up to 1/4 throttle. From 1/4 to 3/4 is your needle taper or clip position, after that it's all main jet. Do a plug chop at each throttle position to find out where your lean or rich.

I'd go to FMF's website and see what jet they recommend for your quad. It will probably just be a starting point unless they specifically mention your elevation. You should probably get a couple jet sizes above and below, or talk to someone in your riding area who has the same mods.

 

I would put in a 155 main. That should do it.

 

i had a 160 main jet and the spark plug was still too white

 

wats a plug chop ????? what would be fmf's website so if the plug is white i have to keep going bigger

 

Was your quad mostly idling, mid throttle, or wide open when you had the 160?

 

everything i drove it up and down the highway i even put a new plug in it to make sure

 

We know how difficult jetting can be sometimes, that's why when we test our exhausts we also adjust the jetting to see what works best. Sometimes stock jetting works fine, other times a slight adjustment is needed. Here is what we've come up for in our area and is a great starting point for you as well. There are way too many variables in jetting to give you a recommendation that works perfect. Use these specs for a reference to help aid you with your specific bike. We developed these specs with a 32:1 fuel to oil mixing ratio of a 50/50 mix of race fuel and super unleaded, 0 - 1500 ft altitude at 70 degrees outside temperature.

Your choice: HONDA --> 2004 --> TRX400EX
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Jetting Information
Main Jet: 150-152
Pilot Jet: 40
Needle: STOCK
Needle Position: STOCK
Power Jet: N/A
Air Screw: N/A
Fuel Screw: STOCK
Comments: Remove airbox lid snorkel

This is off of there website. It's apparently pretty generic, as you can not select the pipe. If your elevation is higher go a little richer. I'm guessing this is an average and I don't know where your pipe lands in their lineup as far as flow, but I'm guessing it's towards the upper end of the range so you probably want to go a little richer any way.
As far as the pilot goes, I'd get the 40 and try that. You have more adjustability with that one anyway. If the brassplug is still there drill it out. With the motor running, slowly turn fuel screw out until it starts to idle down then go back to the point where it idles the fastest. Then adjust your idle back to normal. You may have to turn it up slightly before you do this, but only do it enough to keep it running and only do it if it has died when you already tried.

 

what is the pilot jet??? where is it located?