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View Full Version : Anyone hop up a 400EX motor?



HeepH8erTy
08-14-2013, 07:47 AM
I've been getting bored with my 400ex and am thinking about some performance mods. Was wondering if anyone on here ever built one up and had any advice? My biggest worry with modding the motor is that its air cooled... I know a lot of people have over-heating issues when they start boring them out. I dont want to bore it out (not now anyways) or build a full on race bike or anything crazy. I mainly ride woods, fields, power and gas lines, etc. I dont ride any tracks or MX or do any races.

Here's my plan:

10.5-11:1 stock bore pistion
stage 2 hot cam
full exhaust (not sure what brand yet, kinda worried about noise)
450r carb (jetted correctly)
450r timing chain
Procom CDI box
clean up the ports in the head
back cut the valves a tiny bit

suspension-wise, I was thinking:
450r front shocks (sprung and valved)
stock rear shock (sprung and valved)
xc rear shock link

Anyone have any thoughts on this? Good? Bad? Could be better? Since I am a cheap little mofo, I do like the best bang for your buck. So if you got any cheaper/better ideas, let me know.

oros35
08-14-2013, 09:38 AM
I'm quite pleased with my 400ex. It's an older build, before the 450 was out. Bored to a 426, ported and polished head, Hot cam (stage 2 sounds familar but that was like 10 years ago I built it) valves done, Everything else inside the engine gone over and checked/fixed, FMF header, White brothers E2 exhaust, best clutch I could buy (don't remember brand), Stock carb jetted corrrect.
A little suspension goes a long way. I don't know what is hot and cheap these days.

HeepH8erTy
08-14-2013, 10:00 AM
Do you remember if you are running head studs? And any problems with overheating?

oros35
08-14-2013, 01:44 PM
Not sure on the studs. No problems overheating.

Sycotik Skier
08-14-2013, 01:59 PM
Suspension mods will make it faster. From my understanding 450r suspension bolts right up.

JeepGeneral
08-14-2013, 06:32 PM
I would sell it and buy a 450R, you'll be further ahead for less money.

YZEATER
08-16-2013, 11:30 PM
Have the crank checked, head , valves. If it had a lot of time on it you'll have lots of money in just refreshing it.

john00TJ
08-20-2013, 07:21 PM
my last quad was a 440 big bore an it flat out ran .never over heated an could beat on all day . had the basic full build New JUg ,polished ported head ,Carb ,stage 3 cam with FMF header White Bros exhaust Cdi , Airbox an cleaner mods . I rode a few 450Rs before but id have to say the suspension isn't really worth swapping .. just get some elkas or Axis shocks ..if it were me id put my money into the suspension before the motor expecially woods riding .. youll be faster in the woods with a sweet suspension.. I ran leagers swing arm+2 an A-arms +1 with Axis triple rates an could float threw the woods ..suspension is best bang for your buck IMHO ..