need up grade

[NRTHBUSH]

ok i want to up grade my 400.

already moded is

fmf pipe,
k&N filter no air box lid.

rims with itp hole shot mx tires.

trail tech bars,clamp and speedometer.

im geting ac racing black line nerfs. and a teather kill swich



would an edelbrock carb benifet me. right now the engine is stock. wateing for my warenty to end before i go crazy and put a big bore kit in. geting my taxes back ad want to make my stocker some what race ready.

Carb is last thing on list for the ex. After you port and add cam and bore it out thats when you switch carbs. I got a air box elminator that would let it suck even more air that I would sell you for $15.

[400exrider707]

A 450R carb would be my first choice due to cost and effectiveness, second would be an FCR if price was no concern.

With the mods you have now, I would do piston/cam combo. Its an easy under $300 upgrade and is one of the best power boosters you can do. I would also get the CRF cam chain (same as heavy duty) and a cometic thin head gasket.

Don't for get better head studs.

[400exrider707]

Originally posted by nacs420
Don't for get better head studs.

If you go over 11:1 yes that is recommend as well as upgrading the rod. I like the 11:1 setup myself for the everyday guy, this way you get more power without having to run race gas.

[NRTHBUSH]

what kind of FCR? im asuming single horizontal...????? :S
also what do i do to get rid of the huge starter/ kill swich assembly on my bike.... what options are there?

Originally posted by NRTHBUSH
what kind of FCR? im asuming single horizontal...????? :S
also what do i do to get rid of the huge starter/ kill swich assembly on my bike.... what options are there?

I think people use yfz450 carbs :confused:

Some peope with ex's will get rid of the key and the box on the bars with the light switches/starter button/ kill switch and just rigg up a push button kill switch as the starter. You would then also need to buy a tether kill.

[flauge]

I think a carb would be a good upgrade for you.. Ive got almost the same mods as you do and I added a 450r carb. It made a BIG difference in response and power. So far its the best thing Ive done to my 400 yet:cool:

Originally posted by flauge
I think a carb would be a good upgrade for you.. Ive got almost the same mods as you do and I added a 450r carb. It made a BIG difference in response and power. So far its the best thing Ive done to my 400 yet:cool:

If you talk to any engine builder they will always say carb is last on the list.

[400exrider707]

Originally posted by nacs420
If you talk to any engine builder they will always say carb is last on the list.

who says that? why would that be last? It depends what you're building and what its for.

[NRTHBUSH]

took it for a rip today on the new rims n tires. 20 up front and 18 in the back. thats down from 22 and 20 . front end pops up more easy now. just still can't seem to get my jetting and needle right though :S

does an FCR carb eliminate jetting ? think i read some were on here that it does... or was it the 450R? just seem i hafta re jet all the time and it becomes a pain because ive never realy gotten it right.

Originally posted by NRTHBUSH
took it for a rip today on the new rims n tires. 20 up front and 18 in the back. thats down from 22 and 20 . front end pops up more easy now. just still can't seem to get my jetting and needle right though :S

does an FCR carb eliminate jetting ? think i read some were on here that it does... or was it the 450R? just seem i hafta re jet all the time and it becomes a pain because ive never realy gotten it right.

No you need to jet still. Dont want to get need to make it fuel injection.

Jetting a carb

1. Treat the symptom. Many people isolate the problem or can describe the problem but then treat it incorrectly. For instance, the quad is not performing off the bottom, so they lean the main jet. If you’re having a bottom end issue, treat it first with the air screw and then possibly a pilot jet change. Mid range issues are going to be treated with clip position and full throttle issues with the main jet.
2. Needle clip adjustment is counted from the top. If your told to use the number 4 position, that’s the forth groove down. Moving the needle clip up lowers the needle, leaning the mixture, and vice versa.
3. Two strokes normally have an air screw, so out is lean. The air screw is going to be positioned before the slide.
4. Four stroke carbs normally have a fuel screw, so out is rich. The fuel screw is normally located under the carb, in front of the float bowl.
5. Altitude. The higher you go, the less air you have. Thus, if you go up and have less air, you need less gas, so lean the jetting. A good rule of thumb is lean1 jet size for every 3000 feet in altitude you gain. This is a conservative estimate and you can get added performance by checking the jetting and leaning even more.
6. Air temperature. The colder it gets the more air density you have. Think of air as a liquid which gets thinner as it gets hotter . Air is the same way. If it gets colder you need to add more fuel as you have more air. Your motor also makes more power as it gets colder. A good rule of thumb is every twenty-degree change in air temp is a main jet size change.
7. Don’t confuse speed with RPM when you’re working out a problem. Lets say the motor pulls good off the bottom but cuts out on top. That should be true in virtually every gear. Pulling good off the bottom does not mean running good in first and second gear only. Often a lean motor will run good in the lower gears but then start hesitating when revved hard in top gears. So when working on jetting issues, rpm description is the key.
8. Jet check. To do a main jet check the idea is to run the motor on the main jet and read the plug, isolating the main jet reading. To get a main jet reading, replace the spark plug with a new one. Ride the quad or bike for five to eight minuet s at a moderate pace, vary the rpm and shift up and down the gears. Once the motor is up to operating temp you can make a jet pass. Start in second gear and ride at full throttle through fourth gear fully revving it out in forth gear. With the throttle wide open in fourth hold the kill button down, pull in the clutch and stop. This is called a “plug chop”. Read the plug. With a flashlight and a magnifying glass, look at the porcelain part of the plug only. As you view the plug from the center electrode look down the length of the porcelain to its base. At this point their should be a dark, chocolate-colored smoke ring. Their was not sufficient time to thoroughly color the whole plug so the nose of the insulator will probably still be white as long as there is a visible dark ring at the base everything is ok. A more accurate way to read the plug is to saw off the threads at the washer. This allows you to look directly at the base of the porcelain, thus getting a very good reading.
9. For most trail riding and mx racing, a fourth gear plug chop is all you need to do. If you tend to run it flat out in top gear then make your jet pass/plug chop in top gear. Desert racing and wide open type riding will need a richer jetting than MX jetting.


If you install a bigger carb on a 4 stroke, you should first consider whether it will benefit your model and riding style. Big carbs should be only put on MX,TT, drag racing and some sand riding applications. In trails and woods riding you want super throttle response, low to mid range torque, and gas mileage. Installing a big carb looses bottom end torque even if throttle response is good and costs fuel efficiency.
Unless you are a pro level rider, large carbs should be last on your list of mods.
Its ok to bolt a big carb and pipe on a 2 stroke, but on a 4 stroke its what inside that counts. High compression or big bore pistons, stroker cranks and cams are what make a 4 stroke perform.
Another thing to consider is how much your head flows. Keeping a small port with high velocity is a key to getting performance out of a head. Most people think grinding a big port will flow more air, when in reality it makes for sluggish performance and a nightmare to correctly get your carb. It also will determine what size carb your engine needs. Each engine builder will have his own opinion on the amount of CFM a carb should flow over what your head should flow. A good rule of thumb for performance would be to have a carb that flows10-30 percent more than your port does at its highest lift. This is changing, however with the new style motors with their short rod-to-stroke ratios, lighter components inside the motor and multi-valve heads.

VACUUM-STYLE CARB TRICKS.
One of the hardest carbs to jet is the vacuum slide style carb. These are found on a lot of sport machines, including the z400, kfx400, dvx400, raptor, and even utility quads. They are great for throttle response. Unfortunately, they are not the best high- performance carbs.
With a vacuum carb its best to not open up the airbox right away. Get your main jet set correctly first, which in most cases will be one to two sizes bigger than stock. After that, if the machine is backfiring when you let off the throttle, you can turn the fuel screw out one or two more turns than stock. After that if the machine is backfiring when you let off the throttle, you can turn the fuel screw out 1 or 2 turns than stock. If this does not get rid of the problem, you will have to go up on the pilot jet size and turn your fuel screw back (leaning it back down).
Once you have these set, if you now want to open up the air box, you’ll often have to change the needle. Several companies offer jet kits with needled.
As you open up the air box, you lessen the pressure that allows the slide to lift, so you need to richen the mid range up with a thinner needle. A thinner needle allows more fuel to pass into the intake tract. This can be a trial and error process of learning.

TUNING BY DUCK TAPE.
An easy way to jet this style of carb is by drilling as many 1-1/2 inch holes in the air box cover as you can. Put duck tape over all the holes except one. Then remove tape from the holes one by one until you get the machine to perform at its peak. The more holes you uncover, the more you will have to go up on the main jet. This is wear it gets tricky finding a balance between the richer needle, main jet, and the amount of air that make the machine run at its best. Taking the duck tape on and off will also be a way of re-jetting your machine from winter to summer (different temps) without having to start from scratch all over again.


Troubleshooting:

Quad won't start after a crash
-Pilot too lean
-Idle set too high
-Improper starting procedure
-Quad wants hot start button



*Quad runs on or won't idle down when throttle is chopped
-Idle set too high
-Air leak intake or engine
-Pilot too rich (when bike is hot)



*Quad won't start when cold outside
-Pilot jet too lean
-Air filter is over-oiled
-Motor oil too thick for temperature



*Quad sputters/won't clean out at high RPM
-Main jet too rich
-Air filter is over-oiled
-Spark plug has debris on electrode



*Quad coughs and stalls in slow turns
-Pilot too lean
-Idle set too low
-Valves set too tight
-Decompressor is set too tight, so turning the bars engages release slightly

*Quad hesitates or bogs over deep whoops or G-outs
-Float level too low
-Carb vent tubes blocked
-Main jet splash shield not installed
-Float level too high, gas is trapped in vent tubes (install T-vents)



*Quad starts but won't take throttle without sputtering
-Pilot jet too rich
-Water in fuel
-Debris in main jet



*Quad suddenly starts sputtering/gas flows from vent tubes
-Stuck float check valve
-Debris in gas or carb



*Quad runs hot/feels slow and flat on straights
-Main jet is too lean
-Fuel octane low, causing detonation



*Quad coughs and stalls when you wick open throttle
-Needle too lean
-Slide cutaway too lean
-Pumper circuit blocked or too lean

[NRTHBUSH]

sounds like i need to play with my needle some more. when i realy jam the throttle it just bogs right out like its not geting gas or its geting to much.

[flauge]

Beleive it or not, I didnt loose any bottom end when I put my carb on but I think my stg 1 hotcam might have had something to do with that . For the money tho I dont think it can be beat.;)

[NRTHBUSH]

took the carb apart and the frikan clip isn't even on the needle. it was just sitting there no wonder it ran like a bag of ***** . i found my stock needle and clip and droped that back in. now the spark plug is nice and brown... but i still get the boging when i go hard on the throttle ..... :S pilot is a 42. stock needle now and i belive i have a 155 or 160 main in there . out of ideas. :S

main jet. check the plug if its black you need a smaller one. if its white you need a bigger one.

You could always port the stock carb. If you do it like a funnel you dont loose much bottom end actually can some times gain bottom end when you do it like a funnel.

[NRTHBUSH]

Originally posted by nacs420
main jet. check the plug if its black you need a smaller one. if its white you need a bigger one.

like i stated above my spark plug color is perfect now. bt when i hammer the throttle like im going off the start line it just bogs out and dies. other than that it runs great :S hoe the heck do i adjust my slide. and were can i find a needle clip since i have no clue where the heck my clip went for the dyno jet needle :S wasn;t in the carb.... :S i just stuck my stocker back in becuse i don't think that clip comes off. :S help lol

[NRTHBUSH]

any one know were i can find a needle clip.

[flauge]

You can always call up dynojet and see if you can order another clip from them, they cant be over a couple dollars. They're also pretty cool to deal with too.. I ordered a main jet adapter from them when i broke one on my old carb, so they sent me two just incase i broke another.