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400EX CDI trick

52K views 32 replies 14 participants last post by  DR_ 
#1 ·
I though my fellow 400EX owners would appreciate this little trick to save a few bucks. I got this from www.powroll.com so I can't take the credit.

IGNITION HOP UP TRICK!
Many aftermarket CDI boxes sold for the 400EX are actually stock Honda XR250R boxes. The unmodified XR250 box will give you about 800 more rpm on top and a faster ignition curve. You can purchase this directly from your local Honda dealer and save money.
Order: CDI for Honda XR 250 1992-2004 Part #30410-KCE-671
 
#8 ·
I remeber reading that post Helmut but I went ahead and re-posted it..lol
 
#9 ·
Yeah, it needed a thread of it's own anyway. Not many people will see it hid in the middle of another thread. LOL.
 
#10 ·
would this be beneficial to a quad with just an upgraded air filter and exhaust?
 
#11 ·
It can't hurt. and a lot cheaper than an aftermarket CDI
 
#12 ·
haha alright...

i just ordered one on ebay for $20 haha
 
#13 ·
cool deal you're the guinea pig just so you know Let us know how it works out.
 
#14 ·
definitely will do!
 
#16 ·
Personally I can get just as good performance from a stock CDI that extra 1000 RPM isn't going to do anything your power curve starts to fall off way before redline anyway all you did was increase the red line, and as far as timing curve is concerned you can advance the cam or retard it and get the same effect. doing either of these is to be done with caution since these engine are an interfearance valve train. but this is all my opinion. If you want a cool aftermarket performance CDI by all means.
 
#18 ·
well an aftermarket cdi does more than just raise the rev limit.. a good one will also smooth out all the peaks and valleys in the timing curve creating a smoother power flow balancing it all out, making for nice smooth power building up all the way to the new red line; so your power doesn't fall off short of redline.. this is where all your supporting mods come in such as intake and exhaust. think of it this way, your engine is nothing more than an air pump. the more air you can pump in the more air you need to pump out. hence if you increase the flow of air intake the need to add a higher flowing exhaust increases to pump out the larger volume of air. but now you cause a lean condition in the cylinder so you need to add more fuel to compensate and richen the mixture, this is where jetting comes in. this all causes a need to ignite the mixture at a different time depending upon where you are in the rpm range and how much throttle is aplied and how much load there is on the engine to produce an efficent spark to fire in the cylinder which causes more horsepower.. you see horsepower is a byproduct, a result, not the cause. and this is why an aftermarket cdi box is neccecary once you reach a certain point in your modifications which is also why you see stage 1,2,3 cdi boxes, each one is designed for different stages of modification... stage 1 for simple mods such as basic intake and exhaust, stage 2 for when you go beyond basic and add a cam and possibly a larger bore, and finally stage 3 for when you decide to get really wild and add some head work such as porting and polishing and maybe some bigger valves to flow way more air both in and out and a really agressive cam.

stage 1 would be for fun trail riding, stage 2 for agressive trail riding and some racing from time to time, and stage 3 for all out racing.

hope this sheds some light on things and helps to explain more, what a cdi box does and how to properly choose the one you should be getting for your needs, and why/when you SHOULD be getting one.


BEAST
 
#19 ·
I understand you're point , but from my experiences with aftermarket CDIs I haven't noticed a gain through them at all, and it's very possible it was due to them being a lesser expensive brand? I guess I'm more old school degreeing in cams, hotter coil packs ect, and displacement. lol if you have everything in balance and precise then that same power can be achieved. but we are not here to argue since most opinions that differ will lead to that. lol, I'd say if you want it buy it if not don't. lol

Thank you for the information none the less I'm never too old to learn...lol
 
#20 ·
no. you are right. you will not notice much of a gain at all just through the addition of a cdi box... rather a CDI box is more like the frosting for your cake.. bake your cake (do your mods) then add the frosting (CDI box) you will enjoy the cake more.. lol the cdi simply enhances the mods you have done. and is more for those who have no experience in degreeing cams and setting timing manually. but that is not to say that even someone who degrees their cam and manually adjusts their timing wouldnt see a bennifeit from adding a cdi box aswell.. but there isnt as much need for one for someone who does. and your other note on the aftermarket coil, that is not something I hear mention of verry often, but IS verry bennificial and should also be added at some point in the mod process. the combination of the 2 ( which is why you often see them sold together) is very much like adding an aftermarket (such as MSD6al or a JACOBS) ignition box and coil in race cars.. you may not really notice the difference in performance if you don't really know where to expect to see it.. a hotter coil and a multiple discharge ignition box will give the most noticeable gain and noticable performance increase under heavy load (lugging up a hill in a higher gear or towing) other than that you really wont notice much of a performance increase however you will notice better efficiency and smoother running and only if you are really in tune with your machine on a personal level. ( I can jump on my machine and tell if something is wrong just by how it sounds and feels).. with that said; just because you don't notice it don't mean its not doing its job.. some performance mods arent meant to neccesarily add horsepower but rather to enhance overall performance.

I am not here to step on feet or to start arguments. and you are right, if you want it add it if not don't. but when making the decision make it a fully informed decision and that goes for any mod you do to your equipment, don't just do it because this guy or that said it was good or bad or because your buddy is doing it or your mechanic said it was so. I am simply information sharing from my years of racing experience and research (cars, trucks, boats, bikes, quads, snowmobiles) they all use internal combustion engines and there is alot of information that crosses over through the platforms.

peace
BEAST
 
#21 ·
Agree ^^^ well said, you just wouldn't believe how many young bucks out there think a programmer will make them faster or just adding in a sweet sounding cam..lol Crisp and clean sounding H.P. is what most desire, you what I'm speaking about... you can just tell power from an engine just by the sound it makes, an exhaust dosen't make the sound it only controls the noise. lol
 
#22 ·
So, i swapped the CDI's today.
I took it for a ride with the stock box for a few, and then switched them.
I definitely noticed the higher RPM range, but it didn't really seem to help (like you guys were saying.) It revved higher, but didn't seem to get faster from it.
However, I'm just going off the butt dyno, but it did seem a bit peppier. It felt a tad faster, but if could just be power of suggestion...
Also, I was only riding on my half acre yard so I wasn't really able to go like i'd want to.
 
#23 ·
Well atleast we know now that nothing smoked...lmao. if you can stretch it out you may see a little more topend? I did say may. lol
 
#24 ·
Yup, went in fine and worked without flaw (not saying improvement) also, it also got rid of the reverse limiter and allowed starting in reverse since its from a bike.
 
#27 ·
yup, went in fine and worked without flaw (not saying improvement) also, it also got rid of the reverse limiter and allowed starting in reverse since its from a bike.
well that reverse thing is a plus!! Lol
 
#29 ·
ANd how is this possible? that would be like removing the ECU from your car and starting it up
 
#30 ·
degreeing the cam will not do the same as ignition timing.

degreeing will change when the valves open, ignition changes when the spark plugs are sparked.

the cam is a piece of metal, once its set, its set. you cant advance it in the low end then retard it in the top end, which you can with an ignition box.

degreeing can raise or lower the overall powerband. ignition timing can maximize the effects of the cam and fuel thru out the entire rpm. you can advance ignition timing where aloud and get better performance and fuel economy, lower it where needed to keep from spark knock. you will get more power out of ignition timing then out of degreeing unless the cam was set up poorly to begin with and you will have alot more versatility.

even on a bone stock machine, advances in ignition timing can yeild hp gains if its not knocking along with a smoother powerband. throw in some higher octane fuel and you can really take advantage of added ignition timing.
 
#32 ·
You can just snip a wire (I think it was gray with black) and have that "feature"
 
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