400ex- lots of qustions

[Fenix169motox]

hey everyone its been a while since i've been on here, and well as always my 400ex needs more power but i want to keep it reliable...

i have a few ideas in mind of what i was planning on doing, without tearing the motor down to put in high compression..

first id like to know what you all think about carbs, which one would be more reliable to throw onto the quad? 450r or yfz ...? but i have stock compression, bad idea or not? or am i just better off getting high compression piston and keeping the stock carb?

from there i was thinking of new cams, cheap power right? or am i wrong.. lol i'r rather have mid to high range power increase, i've got all the torque i could need so stage one cams??

What i already have: tc exhaust-jetts, K&N filter, new-stock piston-valves-seals (it used to smoke, and well still does :-( )

i am on a very tight budget and cant really have a motor that might break down every time i go to ride it. Thanks for the help guys!

[northwest Texas]

With what you have, probably the addition of a cam would give you the most bang for your buck. I can't see the carb making that much difference for your engine, not that it won't help a more modified engine.

With a budget, you could get a cam for less than $150 and do it yourself for next to nothing.

[hondaracer57]

i would deff get a cam but if u want mid too top u would have to get stage 2 cam cause stage one is bottom too mid...if u are lookin for reliable i would put a new timing chain too...the 450r timing chain will fit and its cheaper than a 400 chain (crazy aint it) plus if ur quad is still smokin after that work ur valve seals might not of seated right or ur rings didnt seat good..if i were u i would go one size up on ur piston (not sure what the bored is)and get a 11:1 comppression piston that way u can still run pump gas(93 octane)and stage 2 came...so u will need to but 1 over sized 11:1 comppression piston,u will need to get it bored,1stage2 cam,new timing chain (u can get the 450 chain at a honda dealer),gaskets,and just too be safe if ur valve seals didnt seat i would get new ones there prettty cheap anyway...

[400ex28]

Hotcams stage 2

[fastyz85]

i've had the motor mods in my sig for 5 months now and haven't had a problem with it.its just you need to do a valve adjustment after the first 4 weeks or so of riding it because of the new cam.

[Fenix169motox]

yeah its stock bore, and the main reason im dong anything is becuase the timing chain is wore out and is makin my quad a knocking bomb as we call it.. lol but really valve seals were just replaced along with piston and rings, it might be 11:1 i have no idea i just let the man do his thing.. like i said i have no idea whats going on with motors, it sucks.. and i'd rather not learn on mine and not be able to ride it.. :-(

what exactly is the difference between stage one and stage two? and what do you all suggest i to to it, i've got a lot of torque with the set up i have now..

[hondaracer57]

i got mine bored over then next size up from stock with an 11:1 commpression piston and new crf450 timing chain w/stage1 hot cam w/ new oem clutches and its like brand new...

[HEMI426EX]

i have a 2000 400ex, bored to 426, 13:1 compression and stage III cams, curtis sparks header and exhuast, K&N filter with custom airbox, geared sprocket, biggest jets that will fit in a stock carb, and with all this done i run 93 pump gas with lots of octane booster, and ive never been left sitting on a trail, sometime if i've rode all day and cut it off it can be a lil hard to get started but other then that, its a monster of a machine, reliable and very fast, so what i say is build it as much as you want, just having it tuned well and maintained is your relaible factor.

[jmccary]

HEMI426

I was considering doing pretty much the same mods you have to my 2005. Have you had any head gasket issues or studs coming out? I was trying to decide between the 416, or 426. I may even go 440. Haven't decided just yet.

[Fenix169motox]

nah man no problems with the 400, like everyone said, its bulletproof.. i think im just gunna sell it anyway now.. and get me an R!

[400exrider707]

Originally posted by HEMI426EX
i have a 2000 400ex, bored to 426, 13:1 compression and stage III cams, curtis sparks header and exhuast, K&N filter with custom airbox, geared sprocket, biggest jets that will fit in a stock carb, and with all this done i run 93 pump gas with lots of octane booster, and ive never been left sitting on a trail, sometime if i've rode all day and cut it off it can be a lil hard to get started but other then that, its a monster of a machine, reliable and very fast, so what i say is build it as much as you want, just having it tuned well and maintained is your relaible factor.


pump gas on an air cooled motor with 13:1 compression is really asking for it. If its not already messed up give it time. Also octane booster doesn't really do a whole lot of anything except waste your money. Biggest jets that fit in a stock carb? So does that mean that its jetted correctly or you just assumed putting in the biggest meant it would be the fastest? Cause with your mods listed the biggest jet that would fit would be rediculously way too big. Also boring to 426 is not recommended as its the last possible bore on the stock cylinder and the sleeve is very thin, which is not very reliable. Chances are your not even close to 13:1 compression even if thats the piston you put in, as the 400ex piston sits .040 in down from the surface even at TDC.

[400exrider707]

Originally posted by jmccary
HEMI426

I was considering doing pretty much the same mods you have to my 2005. Have you had any head gasket issues or studs coming out? I was trying to decide between the 416, or 426. I may even go 440. Haven't decided just yet.

Piston size doesn't really matter as much as compression ratio on a 400ex. Anything over 11:1 compression on a 400ex, then a heavy duty rod, and heavy duty head studs are highly recommended especially if your trying to build a reliable motor.;)

Originally posted by Fenix169motox


from there i was thinking of new cams, cheap power right? or am i wrong.. lol i'r rather have mid to high range power increase, i've got all the torque i could need so stage one cams??

What i already have: tc exhaust-jetts, K&N filter, new-stock piston-valves-seals (it used to smoke, and well still does :-( )



I just spoke with Hot Cams yesterday on 400EX cams.

Here's what they said -

A high compression piston would help all thru the rev range.

Comined with a cam, that'll really wake up the 400EX everywhere.

Stage 1 is for mid to high rev, with more toward mid range. Good for trails, and tighter areas.

Stage 2 is for mid to high rev, more toward high. Good for track and dunes, and wide open areas.

I'm going with the cam and piston myself.

[400exrider707]

Originally posted by garandman


I'm going with the cam and piston myself.

Thats thee single best mod for a 400ex once the exhaust and air intake are opened up.

[Fenix169motox]

Originally posted by garandman
I just spoke with Hot Cams yesterday on 400EX cams.

Here's what they said -

A high compression piston would help all thru the rev range.

Comined with a cam, that'll really wake up the 400EX everywhere.

Stage 1 is for mid to high rev, with more toward mid range. Good for trails, and tighter areas.

Stage 2 is for mid to high rev, more toward high. Good for track and dunes, and wide open areas.

I'm going with the cam and piston myself.


ok so what compression are you doing? 12:1 or what? if i had the money i'd like to make it a 440 long stroke, but thats like $2000, well thats at least how much my buddie paid for it..

Originally posted by Fenix169motox
ok so what compression are you doing? 12:1 or what? if i had the money i'd like to make it a 440 long stroke, but thats like $2000, well thats at least how much my buddie paid for it..

Its either the 10:1 or 10.5:1, so I can still run 93 octane pump gas.

[HEMI426EX]

theres always a wise *** in the group that has to try and put down somebodies ride. just becouse i built my bike to run wide damn open and thats all dosent mean its set up for everybody, i dont like sitting still, i wanna be balls to the walls goin for it, and to answer your smartass comment about the jetting, a honda tech thats worked on qauds, motorcycles and dirtbikes for 12+ years jetted the carb and it runs fine. so i appreciate your attention to trin to make somebody look stupid, its very kind of you.

[Fenix169motox]

so hey, does anyone know how much it would cost to big bore (440 ? anything that'd have more power :) ) port+polish, .. well what else does anyone suggerst? better yet! i've got about 1200 to spend on this thing, motor's completely stock, but i have a stage one hotcam ready to put in, what do you smart ppl suggest i throw into the motor? i dont need anything spectacular, just something i can rely on to have some power when i need it.

thanks guys!

[northwest Texas]

I just spent about half that going to a 426 on mine. I sent the top end off to Colby and he had a new sleeve installed for me. Ported and polished the head, moly coated the piston and I put it back together and I swear it's not the same engine.

I've only had the chance to ride it an extended period of time just once but where I was running out of power before, she just powered right through like it was nothing.