new pipe, tires, filter, jets....slower than stock

[mcfly]

ok so what gives...ive been sand drag racing with my stock 03 400ex for the past few weeks and have been quite impressed with how close i am able to stay to the larger 450r's and yfz's. however i have noticed, surprisingly, that most of the piped and jetted 400's are being eaten for lunch by my completely stock quad.

i decided to close the gap a little on the bigger bikes and pipe and jet mine. i bought an fmf powercore 4 slip-on that has been shortened a couple inches, a k&n filter with outer wear, completely removed the airbox lid, installed a 42 pilot and 160 main jet (keihen), and installed a set of 20" holeshots on 8" douglas wheels. i was immediately impressed with how well the holeshots hooked compared to my bald stockers. i didnt much like the noise coming from the pipe, but if its fast, i can live with it. my problem is, now i'm the one getting outrun by bone stock 400 ex's and my gap vs the larger bikes has increased rather than decreased. i even tried using a pair of 19" gecko paddles to no avail.

where did i go wrong? i understand that there are differences between pipe manufacturers, and some pipes may perform better than others. but ANY aftermarket pipe should increase, not decrease, performance.

i weigh approximately 200 lbs and our elevation is nearly 1000' above sea level.

any help would be greatly appreciated.

[prepracing]

yeah... that definately sounds weird :confused: when u changed your jet u didn't happen to somehow mess up your throttle linkage, maybe your not gettin all your throttle ? I dunno man thats just strange. Only other thing I could think of is whoever shortened the pipe may have messed of the insides and its just not flowing like it should. But your right about any kinda pipe and especially a K & N filter should have increased power. Good Luck, keep us posted on the findings

[mcfly]

the inside of the pipe is flowing fine and has fresh packing. i had my mechanic install the jets to be sure the linkage was adjusted properly afterwards. i called fmf today and at 1000' above sea level they recommend going leaner than i did. they are calling for a 150-152 main. i wouldnt have thought that difference would be noticeable, but i'll try it anyway. if anyone else has any thoughts id greatly appreciate the advice.

[vinson581]

too rich and its going to fall on its face....check your plug and get back to us

v581

[quad2xtreme]

Did they recommend you change the pilot to a 42? I used the Dynojet kit on mine and only had to change the needle and the main jet. I got good improvement over stock and I only changed the air filter (White Brothers) and opened up the airbox lid. I did a little work grinding down the ridge on the stock headpipe with a dremel. I've done this to all 3 of mine and each one is faster than a stock 400ex throughout the entire powerband. Even replacing the exhaust, Dynojet doesn't recommend any change to the pilot.

You can go to their website (www.dynojet.com) and download the instructions for installing their kit. It is in pdf format.

/Jon

[mcfly]

the 42 pilot jet provides a much needed improvement for cold starting. my 400 rarely idled at all until fully warmed up and even then it would die if you tapped the throttle. its a pretty common event on 400's and a simple fix.

dynojet uses a shallower taper on their needle which is a cheap shortcut to the same end result as richening the slow speed jet. it allows slightly more fuel to flow past the needle during acceleration from idle to about half throttle.

[cals400ex]

i would try another set of stock tires. my shredders really slowed me down too. no one will notice it unless you race some one that has a bike similar as yours on a regular basis. i do that and i found out my bike was slower, especially in the upper gears.

[mikeboone]

Maybe have lost power when jetted? Remove the airbox and open the throttle while you look down back of carb. Be sure the slide is FULLY opening.

Also, does it smoke black or backfire--pop?

Dynojet uses a different scale as opposed to Kehin so it's hard to say what # jets you may need but I would think your main is too lean with all additional airflow available. put ht elid back on and run it. If it runs better with the lid on then you need to bump the jetting up.

It has been several years since I had a stock 400ex carb but isnt the stock pilot jet a 48?

[mcfly]

my mechanic took my questions as an affront to his abilities as a mechanic and isnt very receptive to the idea that my bike may need a bit of fine tuning on the jetting. this all comes as a total shock to me since he has been wonderful to me and has offered some great advice in several areas until now. currently im runnin all keihen parts in my carb. k42 pilot (k38 stock) k160 main (k148 stock)(fmf calls for a k150-152) when i run with lid off or with the lid on but propped up on one end...it seems to run fine with no smoke or popping at all....but its slightly slower than stock. i have to muster every ounce of my riding ability to stay with a stock 400. when i put the lid on and completely latched into place it runs fine while putting around, but spits and sputters upon serious acceleration. am i guessing correctly when i think it might be a bit rich? there is no smoke, popping, or any other negative feedback from the bike...except its slower than it was in stock trim.

i will remove the airbox tonite and check the throttle adjustment to be absolutely sure.

[mcfly]

the throttle is opening all the way

[mikeboone]

How many turns Out on the fuel screw?

[JOEX]

I'd do what cals400ex mentioned, try a different tire set up. There may be a considerable difference in weight of stock set up to a 20" tire on 8" rim set up. It's part of the fine tuning;)

[400exstud]

I think you must be a bit rich because I have an HMF full system w/ quiet core and the airbox lid on and run a k160 main jet. I am rich and we have a close setup so you may be rich too.

[mcfly]

i havent been able to check the turns on the air/fuel screw because its such a pain to get to. but i will check that as soon as i get a chance. if im guessing correctly, shouldnt it be around 3-3.5 turns out?

[cals400ex]

i would try a set of stock tires. you may have no way to get some unless you buy them, i don't know. that made a noticable difference on my bike. very noticable actually. those rear tires may sit a little taller too. it may not hurt to try 15/39 gearing too. i would start around 2.5 turns out from lightly seated on the fuel screw



if it is hesitating under acceleration with the air box lid on, you are too rich (with the air box lid on). i would run around a keihin 152 (for starters ) with teh air box lid on. with it off, i would run around a keihin 158. a lot of people like to run their bikes richer than i do though.

[SRH]

Originally posted by mcfly
ok so what gives...ive been sand drag racing with my stock 03 400ex for the past few weeks and have been quite impressed with how close i am able to stay to the larger 450r's and yfz's. however i have noticed, surprisingly, that most of the piped and jetted 400's are being eaten for lunch by my completely stock quad.

i decided to close the gap a little on the bigger bikes and pipe and jet mine. i bought an fmf powercore 4 slip-on that has been shortened a couple inches, a k&n filter with outer wear, completely removed the airbox lid, installed a 42 pilot and 160 main jet (keihen), and installed a set of 20" holeshots on 8" douglas wheels. i was immediately impressed with how well the holeshots hooked compared to my bald stockers. i didnt much like the noise coming from the pipe, but if its fast, i can live with it. my problem is, now i'm the one getting outrun by bone stock 400 ex's and my gap vs the larger bikes has increased rather than decreased. i even tried using a pair of 19" gecko paddles to no avail.

where did i go wrong? i understand that there are differences between pipe manufacturers, and some pipes may perform better than others. but ANY aftermarket pipe should increase, not decrease, performance.

i weigh approximately 200 lbs and our elevation is nearly 1000' above sea level.

any help would be greatly appreciated.

hey did you buy that pipe and filter off me a year or two ago? i left completely stock jetting with that setup and my 400ex ran witht he plug tan and nice increase over stock power too

[mcfly]

no i bought this pipe from a different guy and the filter from yet another guy on here. and i did try it with the stock jetting, which didnt seem to work well at all.

cal i have the original tires and will try that. however you say with the lid off i should be jetted near a k158...i am using a k160 with the lid off...the jump from 158 to 160 isnt gonna make nearly the difference i would have to make to get back to stock performance.

the holeshots were the same size as stock (20") but when stood next to each other the holeshots are a noticeably larger diameter.

[cals400ex]

try the stock tires. the holeshots should be 1 inch wider than stock.

the 158 to 160 will not make a huge difference. i would try the tires first.

[bubba power]

the 42 pilot is too big try a 40 i`ve built alot of ex's mostly 440,s.i've used a42 pilot on them,but i think your close on the main jet,if you go back to a40 pilot. the pilot jet fuel circuit is still flowing fuel at higher rpm's. try air screw tuning by:cuttingdown avery small screw driver to fit air screw. start bike turn idle down some , turn air screw in until ready to stall then start turnig air screw out . the rpm's will increase go until the idle starts going down then back off alittle that process should get you real close . you might have to make a fine adjustment.