how to move needle in 400ex carb

[xtullyx16]

okay everyone........ i need a detailed descriptions of how to move my needle in my 400ex stock carb ... it seems to be bogging a lil in 2nd and 3rd and low 4th maybe but is great of the start and 5th. I need to know how to and if i move it down or up whats it do..... and if i need to remove everything or can i get to it without taking off all my plastics.. thanks i dont wanna mess this up soo please make it detailed!

[400exstud]

For your mods, the stock needle position should be golden. I would check into the main. Many people mistake the bogging when it is usually caused by the main.

[xtullyx16]

you think

[xtullyx16]

smaller size?


ik its barely bigger rgan the stock size

[GPracer2500]

I agree that the stock needle clip position is most likely just fine.

When you're evaluating jetting focus more on throttle postions and less on RPM or what gear you're in. The different jetting circuits within the carb are linked to throttle postion.

idle to 1/4: pilot circuit
1/4 to 3/4: needle
3/4 to WOT: main jet

There is some overlap between the circuits but each circuit dominates it's respective throttle position.

That said, I should also mention that sometimes a miss or stumble will only show up in certain gears or certain RMPs. What's actually happening is the engine is responding differently under different loads. So, even if a jetting issue only shows up under a certain engine load, it's still the throttle postion you want to focus on to figure out which jetting circuit is amiss.

Hope that helps.

[xtullyx16]

ehhhh wait..... u lost me lol...... im just saying this cause i draged my friends pred 500 and it pulls sooo much faster in 2 through 3rd and it never did that before but i hang with it in 1 and up int wide open i start cathcing it lol

[400exrules]

Originally posted by GPracer2500
I agree that the stock needle clip position is most likely just fine.

When you're evaluating jetting focus more on throttle postions and less on RPM or what gear you're in. The different jetting circuits within the carb are linked to throttle postion.

idle to 1/4: pilot circuit
1/4 to 3/4: needle
3/4 to WOT: main jet

There is some overlap between the circuits but each circuit dominates it's respective throttle position.

That said, I should also mention that sometimes a miss or stumble will only show up in certain gears or certain RMPs. What's actually happening is the engine is responding differently under different loads. So, even if a jetting issue only shows up under a certain engine load, it's still the throttle postion you want to focus on to figure out which jetting circuit is amiss.

Hope that helps.

so, lets say your puttin along in 3rd at like 2,000 rpm, and you give it WOT all the sudden, if it bogs, does that mean its your main...even though you just mashed the throttle wide open and the rpms are still low because it hasnt accelerated yet, its your main because the throttle is all the way open right?

i hope that made sense:ermm:

and where does the fuel screw come into play?

[GPracer2500]

Originally posted by 400exrules
so, lets say your puttin along in 3rd at like 2,000 rpm, and you give it WOT all the sudden, if it bogs, does that mean its your main...even though you just mashed the throttle wide open and the rpms are still low because it hasnt accelerated yet, its your main because the throttle is all the way open right?

i hope that made sense:ermm:

and where does the fuel screw come into play?

Yes, if you're at WOT it doesn't matter what rpm your at--the main jet is the primary carb circuit in play. I think you've got the idea, but I'll elaborate:

Ok, the scenario is you're in 3rd, 2000 rpm, and quickly hit WOT at lower rpm and it bogs.

If it's a short bog that quickly clears up than it's probably caused by the temporary lean condition that occurs when wacking the throttle open quickly from lower rpms. This happens because it takes the carb a moment to respond to the sudden increase in airflow through the carb. The engine starts sucking lots of air but the carb's ability to deliver fuel lags behind a little. The accerlerator pump (assuming the carb has one--stock 400EX carb does) is there to correct this condition but APs are not perfect. APs can be one of the toughest parts of a carb to tune well. Many AP equiped carbs aren't even designed to have the AP tuned. APs squirt a shot of raw fuel into the engine when the throttle is wacked open quickly--move the throttle slowly and the AP doesn't activate.

However, once the carb catches up with the engine and the main jet starts to meter is full supply of fuel, the temporary lean condition passes. Now you're on the main jet. If the engine continues to bog, sputter, or "load up" than the main is too rich. If it begins missing, popping, and acting like it's running out of fuel the main is too lean.

In evaluating a main jet it can be useful to do what you described--let the engine rev down to a low rpm and then hold WOT in an upper gear. If your main is lean or rich then the symptoms of richness/leaness are usually amplified and easier to detect under high load, lower rpm conditions. An engine with a rich main may load up and stumble badly when holding WOT at 3, 4, or 5 thousand rpm but the condition may not be noticable at 8+ thousand rpm.

Regarding the fuel screw, it is part of the pilot circuit. The fuel screw and the pilot jet work together to determine the fuel metering of the pilot circuit.

[xtullyx16]

im pretty sure my spark plug is reading gold or like brownish red

[xtullyx16]

well im just frustrated cause i race my bros yfz and he gave me a 5 sec lead and he crushed in like 3 acres .... its gotta be jetted bad... hes only got a pipe he shouldnt be killing me by like 5 lengths!

[GPracer2500]

Only a fully built 400EX is gonna stand a chance against a YFZ.

[400exstud]

Your jetting is fine.

You just have to face the facts. Your bike is pushing no more than 28 hp MAX. His YFZ is probably somewhere around 43 hp. It is just that much faster.

[400exrules]

Originally posted by GPracer2500
Yes, if your at WOT it doesn't matter what rpm your at--the main jet is the primary carb circuit in play. I think you've got the idea, but I'll elaborate:

Ok, the scenario is you're in 3rd, 2000 rpm, and quickly hit WOT at lower rpm and it bogs.

If it's a short bog that quickly clears up than it's probably caused by the temporary lean condition that occurs when wacking the throttle open quickly from lower rpms. This happens because it takes the carb a moment to respond to the sudden increase in airflow through the carb. The engine starts sucking lots of air but the carb's ability to deliver fuel lags behind a little. The accerlerator pump (assuming the carb has one--stock 400EX carb does) is there to correct this condition but APs are not perfect. APs can be one of the toughest parts of a carb to tune well. Many AP equiped carbs aren't even designed to have the AP tuned. APs squirt a shot of raw fuel into the engine when the throttle is wacked open quickly--move the throttle slowly and the AP doesn't activate.

However, once the carb catches up with the engine and the main jet starts to meter is full supply of fuel, the temporary lean condition passes. Now you're on the main jet. If the engine continues to bog, sputter, or "load up" than the main is too rich. If it begins missing, popping, and acting like it's running out of fuel the main is too lean.

In evaluating a main jet it can be useful to do what you described--let the engine rev down to a low rpm and then hold WOT in an upper gear. If your main is lean or rich then the symptoms of richness/leaness are usually amplified and easier to detect under high load, lower rpm conditions. An engine with a rich main may load up and stumble badly when holding WOT at 3, 4, or 5 thousand rpm but the condition may not be noticable at 8+ thousand rpm.

Regarding the fuel screw, it is part of the pilot circuit. The fuel screw and the pilot jet work together to determine the fuel metering of the pilot circuit.

ok cool, thanks man...it all makes sense now:D

what i dont understand is, whenever i change out my sparkplugs (i usually do it for the heck of it when i adjust the valves)....the spark plug is black, like its running rich......but it runs great, no sputtering, hesitation, backfiring...nothing. but mind you, this is just when i take the plug out, this is not after a correct spark plug test...ive never done one of those.

[GPracer2500]

Originally posted by 400exrules
ok cool, thanks man...it all makes sense now:D

what i dont understand is, whenever i change out my sparkplugs (i usually do it for the heck of it when i adjust the valves)....the spark plug is black, like its running rich......but it runs great, no sputtering, hesitation, backfiring...nothing. but mind you, this is just when i take the plug out, this is not after a correct spark plug test...ive never done one of those.

Which part of the plug are you looking at? The threaded part that is exposed in the cylinder is almost always black. The part that is used to indicate jetting is the white ceramic part surrounding the center electrode.

Personally, I rarely use plug readings when jetting. Some say todays modern unleaded fuels with all their additives and whatnot don't give accurate plug readings anyway [shrug]. In my experience a plug might be able to tell you if you're WAY to lean/rich but that's about it. Looking at plugs never tells me anything I didn't allready know from riding and hearing the bike anyway.

[xtullyx16]

soo then tell me what i would need if i did a 416 kit running on pump fuel and how much?? soo i can catch my bros 450

[GPracer2500]

A 416 on pump gas isn't going to hang with a YFZ.

[cals400ex]

http://www.exriders.com/vbb/showthread.php?threadid=19832

[400exstud]

Originally posted by GPracer2500
A 416 on pump gas isn't going to hang with a YFZ.

Nope. It would take a highly modified 440 to HANG with one. By this point your bike would be ready to explode anyway.

If you are that set on beating him I know of a few dealers that will sell you a 450 of your choice.

[400exrules]

Originally posted by xtullyx16
soo then tell me what i would need if i did a 416 kit running on pump fuel and how much?? soo i can catch my bros 450

its possible, but only if the 450 is completely stock, and you were running race fuel

[xtullyx16]

man im never gunna catch him! lol this sucks! what if i put a 450r in my frame what i need besides a 450r carb?? lol would i be able to catch him then??

[400exrules]

you could prob do it with a 13:1 416 piston, hd rod, hd studs, P&P, carb, CDI, intake, full sparks, stage 2 cam, and you would have to run race fuel.

if that wouldnt do it, a 4mil 460 stroker would

[xtullyx16]

lol **** screw it! Ill just save money for a full hmf exhaust

[400exstud]

The cheapest way it just to get a bigger quad.

[ohsobad_chevy]

Originally posted by xtullyx16
lol **** screw it! Ill just save money for a full hmf exhaust

dude...Like he said... The 400ex is not made to run with the 450's, you have to face that fact... You are going to dump a chit load of money into your 400ex, just to make it keep up with his STOCK 450. If I were you, I would buy a 450r. The 400ex is a good machine, dont get me wrong(I got one myself) but when I bought mine, I wasnt expecting it to keep up with 450's, that wasnt my concern, I wanted a good trail/play around quad. The 400ex does all I need it to do. I will eventually buy a 450, but I wanted a 400ex as well. :cool:

[xtullyx16]

if i get a 450 it will be the yfz cause it ripps past all others 450r that my bro has raced and it just has a gytr pipe

[400exstud]

Who is the better rider?

[ohsobad_chevy]

Doesn't matter what 450 you choose, The Honda 450r and yfz450 are the same(gearing is different from the factory). Either one of them will roast a 400's arse. 400's are very good trail quads for that matter.