400ex Help???

[f4istunna]

Recently bought a 02 400ex for a good price that was said to need timing chain.

I messed w/ it the other day put a new plug in and got it to start but would puke when you give it gas and popped/backfired out of the carb.

Sound like a timing problem to me but i dbl checked several times everything lines up. Could it be stretched chain? supposed to have a good tensioner in it...

Just looking for some input before i dish out the cash for a timing chain if thats not even it.

[hornetgod13]

Sounds like a jetting issue. What mods and jets does the quad have installed?

[oleboy87]

check your jetting!

[f4istunna]

i considered jetting problem at first but when everyone told me timing chain it started to make sence lol.

It has a bills pipe, 426 piston, hotcam i beleive the heads stock other than cam.

Ill check the carb out. Any idea what sizes i should start w/ on the jetting

thanks again for the help guys

[hornetgod13]

Those jetting specs are out of my league. My quad is more stock than that. I know others on here are closer to your set up and give you jetting recommendations. You could also search old jetting threads to find a good starting point. I would start with jetting first. I think that's more of an issue with your quad. Another thing that might cause it would be the cam being put in 1 tooth off either way. That's just a guess really.

[f4istunna]

ya the cam marks are pretty much right on, i checked the tgiming several times just to be sure. piston tdc and all the marks line up w/ lobes down.

Ill do a search for jettin info. I never really messed w/ jetting much. my rap is injected and any carbed bikes i always had my buddy do it but he moved out of town so looks like im going to learn a thing or two lol

[f4istunna]

jet size was 48 I cleaned the carb and jets out pretty good going to see if that makes a diff. anyone know if its the right size for the mods

No airbox lid, stage 2 cam, 426 piston, bills pipe. (i think the headers stock just slipon)

[hornetgod13]

Stock jets are 38K Pilot Jet and 148K Main Jet. You should have considerably larger main jet and perhaps a 40K or 42K pilot jet. Based on what you posted earlier I'm even more convinced that you should rejet the quad.

[f4istunna]

thanks for the info. Ive never jetted a carb, i had it apart yesterday doesnt look too complicated. Do i just buy an assortment of jets and start somewhere around the jets you mentioned and work from there?

Wheres the best place to get a jet kit that will have the sizes ill need?

thanks guys

The jet i was looking at was inside the bowl? on the bottom of carb and had a needle going through it. I cleaned the others but couldnt see sizes on them just had a star assuming for keihn.

[vett_09]

A jet kit will come with a variety of main jets because evaluation plays a factor in what size main jet you should run. My advice is while you have it all apart, get a jet kit with a new needle as well. Go through and change the pilot, main, and needle. Your quad will run better and start easier.

You can buy jet kits online, or at a local cycle shop.

[f4istunna]

thanks hopefully the jetting is all thats wrong w/ it. Would be nice to not have to get into the motor lol.

Any idea where i should start or what symptoms will come from jetsize being too small or too lorge? just want to know what to look for so i know which way to go


thanks again for the replies

[vett_09]

Originally posted by f4istunna
thanks hopefully the jetting is all thats wrong w/ it. Would be nice to not have to get into the motor lol.

Any idea where i should start or what symptoms will come from jetsize being too small or too lorge? just want to know what to look for so i know which way to go


thanks again for the replies

Pull your spark plug. If it's white, you're running lean - if it's black, you're running rich. It should be a nice tan color when your jetting is correct.

[hornetgod13]

www.jetsrus.com sells an assortment of both main and pilot keihin jets. The pilot jet should be a 40K or 42K. The main jet should be in the 160's depending on the air box lid and if it's installed or removed. With the Air box lid off it would be high 160's and with the lid on start in the low 160's. Keep in mind the is just a starting point. A plug check is the best way to determine. A white plug is too lean and Black plug is too rich. I would buy 40K 42k pilot jets and 158K, 160K, 162K, 165K and 168K main jets. If the mid throttle is not running right I would lower the clip down one slot on the needle.

[f4istunna]

thanks for the tips and refrences
Im going to see if anyone has a jet kit in stock for this today. If not ill order one.

i didnt think the jetting being off affected it that much. It pops/backfires out fo the carb pretty bad and the motor dies(freezes up for an instant) when you give it gas

Im going to try and get a jet kit ill stay posted to how it works out.

[hornetgod13]

Back firing is an indication of a possible lean condition. If you install larger jets and adjust the needle clip, you should see an instant improvement. I'm not a fan of jet kits. They are over priced and you get a lot of jet sizes you will never use. I purchase individual jets at a fraction of the price.

[f4istunna]

ok finally got a few jets to get started, only thing in stock was 158 and 165 so i took them. Went home took the carb back apart cleaned it up real good, adjusted the screw to 2 1/2 turns out. changed oil and fresh gas.

158 it started right up no choke but bogged out when give it gas

so i put the 165 in to see how it ran, started right up but idled a little higher and popped/backfired as soon as you hit the gas wouldnt rev out. pulled the plug out it was black (but it was carboned when i put it in should have got a new plug but i copmpletely forgot)

At least it stays running now thats a big improvement, any suggestions on what i should do next

stage 2 cam, bills silencer (maybe full pipe cant tell if header is a/m, no lid or filter onm when i tried to run it, 426 piston

any help is much appreciated

thanks

[f4istunna]

and w/ the needle clip what exactly is it? and how do you adjust it if needed?

im sure i saw it when i had the carb apart but i have no manual here to look at.

I saw a few needles in the carb but didnt look to be adjustable

[f4istunna]

i went back into the carb to hunt for the needle. Found something that may be the problem

Under the cover where you attach the throttle cable ont he carb theres a little jet (not sure name) it says 110 on it looks like, but right beside that there a hole w/ an oring in it looks liek a jet should go there but nothing in it. Am i missing a part? assuming its not supposed to be like that.

the airtube that connects to the bottom of airbox isnt attached either does it need to be on???