400ex mods
#1
03-14-2018, 04:07 AM
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400ex mods
Hey guys I just picked up a 400ex that has a few mods on it already (it was my buddies atv ) I’ve ridden it many times and it’s faster than any 400 that I’ve raced, or that he has raced , several claiming to have work ,but it’s mine now and I wanna take it up a notch, looking for the next step ? This is what I know about it ...
2000 400ex
Stock sprockets
Stock carb jetted to slip on and open lid I
Larger piston
Stage 2 cam
Removed air box lid
Uni w outerwear
Big gun slip on - stock head pipe
I was looking at fmf powerbomb header pipe & 06 flatslide 450r carb , I’ve raced against this quad many times with an 84 atc 250r after many mods and couldn’t beat it ! very close but just couldn’t , we even switched riders , im twice his weight and the 400 still would win I only beat it with a 350x atc and not by much unless racing up hills, and only 3 outa 5 times, so I thought I’d ask the pros what’s my next step ? I’ve ordered cosmetic stuff for it , how can I squeeze out a bit more ?? Will the powerbomb help ? Or any other larger head pipe ?
2000 400ex
Stock sprockets
Stock carb jetted to slip on and open lid I
Larger piston
Stage 2 cam
Removed air box lid
Uni w outerwear
Big gun slip on - stock head pipe
I was looking at fmf powerbomb header pipe & 06 flatslide 450r carb , I’ve raced against this quad many times with an 84 atc 250r after many mods and couldn’t beat it ! very close but just couldn’t , we even switched riders , im twice his weight and the 400 still would win I only beat it with a 350x atc and not by much unless racing up hills, and only 3 outa 5 times, so I thought I’d ask the pros what’s my next step ? I’ve ordered cosmetic stuff for it , how can I squeeze out a bit more ?? Will the powerbomb help ? Or any other larger head pipe ?
Last edited by 4bratsdad; 03-14-2018 at 04:12 AM. Reason: Punctuation
#2
03-14-2018, 08:43 AM
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Sounds like you got yourself a pretty nice 400ex already. Yes an fmf header will help.
It really depends on what you want, weather its top speed, low end power, acceleration etc. By changing sprocket sizes you can get a lot more top end but then you will loose low end power/torque.
You could reduce a little weight by removing the parking break.
Really depends on what you want, sounds like you have most of the mods covered though
It really depends on what you want, weather its top speed, low end power, acceleration etc. By changing sprocket sizes you can get a lot more top end but then you will loose low end power/torque.
You could reduce a little weight by removing the parking break.
Really depends on what you want, sounds like you have most of the mods covered though
#3
03-14-2018, 10:33 AM
Well...it's a thumper, so typical "car" mods will be your next direction, but the "next level" comes at a price. Here are some other mods:
1) port & polish the head
2) shave head or reduce gasket thickness (to raise compression)
3) larger carb or have stocker rifle bored
4) stroker kit (that'll really wake it up)
5) weight reduction (lighter wheels/tires, shaved plastics, replace metal hangers with zipties, replace steel with aluminum/carbon fiber where possible, etc)
6) add NOS (and hold on!!!)
1) port & polish the head
2) shave head or reduce gasket thickness (to raise compression)
3) larger carb or have stocker rifle bored
4) stroker kit (that'll really wake it up)
5) weight reduction (lighter wheels/tires, shaved plastics, replace metal hangers with zipties, replace steel with aluminum/carbon fiber where possible, etc)
6) add NOS (and hold on!!!)
#4
03-15-2018, 12:00 AM
Join Date: Feb 2010
Location: springfield, illinois
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Thanks I don’t know that I’ll go to that extreme , I’ll order the fmf header , I have another buddy that has a shop and he warned me to stay away from the 450r carb said I’d be asking for trouble but he’s not a mod guy everything by the book , he also talked me out of the 450r said I’d be constantly doing expensive engine work to get a 400 couple bolt on parts I’d be good , I had the wheels& lighter tires be on it soon , I do not know exactly what has been done ? The guy who built it races professionally he did the mods before switching to Suzuki 450
#5
03-15-2018, 06:46 AM
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Well I ordered the fmf powerbomb , like I said before I do not know exactly what had been done to the bike , I know the guy my buddy got it from raced it and that was st least 10 yrs ago and it does seem to be faster than any 400 he or I raced that “ had work “ but hell, they could all be stock ! He said it had the cam I can see the big gun slip on , it has the nicer bumper nerfs handlebars etc on it , just thought I’d squeeze a bit more out of it seems like if I do the carb & powerbomb I could maybe do slight sprocket change to get a bit more top end , i picked up a trail tech computer for it , I’ve heard by couple people that the rev boxes do nothing for them ? Or at least it’s not noticeable ?
#6
03-16-2018, 10:57 AM
#7
03-20-2018, 03:40 PM
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You can also put a stage 3 CDI and a revbox on it. I have it on mine and I have noticed a huge difference in the way the engine responds. I have a slip on HMF, I am bored twice over (.426), stage 2 hot cam, and ti valves. Oh and a K&N filter with the top off. I absolutely love the power and response it has. I just need to get the suspension right. But the CDI and revbox is what I would do!
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#9
03-31-2018, 01:46 AM
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#10
03-31-2018, 01:48 AM
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You can also put a stage 3 CDI and a revbox on it. I have it on mine and I have noticed a huge difference in the way the engine responds. I have a slip on HMF, I am bored twice over (.426), stage 2 hot cam, and ti valves. Oh and a K&N filter with the top off. I absolutely love the power and response it has. I just need to get the suspension right. But the CDI and revbox is what I would do!