CDI box question

[quadmanw]

I'm gonna by the curtis sparks timing key and i heard that a cdi box will help give the 400 some extra spark. does anyone have a preference for a curtis sparks cdi box or white bros?


Thanks, Steve

[honda400ex2003]

i wouldnt waste my money on a box or a coil. both are a waste since the coil doesnt really do much spark wise and the box will not be any benefit since the 400ex doesnt make nearly enough power up high enough in the rpms for it to matter if you have another 100 or even 1000 rpms. I would save my money and put it toward something a bit more useful. there are alot of us with some pretty highly modded engines but 2 things you wont see on any of them are coils and cdi boxes lol. steve

[quadmanw]

Thanks man. Do you still think its worth the 20 bucks for the timing key without the box?

[honda400ex2003]

def! just dont waste your money on the box. steve

[honda400ex2003]

i was referring to the monster coil when i was talking about that also. i have one on my machine lol no use in wasting the money to try it. I guess i was the guinea pig this past spring since no one on here had one that i knew of to get any feedback from. lol steve

[DragonGunner]

10 yrs. on a White Brothers CDI rev. limiter...Its been on stock motors an built motors. Ported head, 3 angle valve job, high compression.....I can't see not having a rev limiter...without it it reaches the upper revs an just starts cutting out. I had a blown head gasket on my race motor an had to throw my boy's stock motor on for the last 2 races, the first race sucked, less power but it was a very tight Grand Prix race, tight woods an MX track...it kept reving an cutting out too quick....then realized I had the stock CDI box...changed it out for the next race an the improvement was like night an day an last race of that year took me to 2nd....even beat the champ that day. A CDI box is one thing I will always recommend as one of the top 5 things to do to a 400EX. I will also mention that in very cold weather its a little bit harder starting, sometimes impossiable, so alot of times in winter I'll put the stock one back on.

[quadmanw]

So many dudes say it is not worth buying one. But on the other hand there's that handful that say its a must. The way that I ride... I over rev alot. But I still dno if I should get it.

[honda400ex2003]

imo shift sooner or re-gear. if you are over revving that much then a different change is in order imo. steve

[Honda5]

Will never run without one. We raced the 400exs for 6 years and if you mx and didn't have one you got left behind! The haters say you don't build power up there but what they don't say is if you shift earlier you are down in the power curve and it takes longer to get back to the higher part of the rpm curve. Take the quad to a 1/8 mile drag strip and do some runs there is a difference why do you think all the racers used them. Anyway you can get them for around $50.

[DragonGunner]

Originally posted by Honda5
Will never run without one. We raced the 400exs for 6 years and if you mx and didn't have one you got left behind! The haters say you don't build power up there but what they don't say is if you shift earlier you are down in the power curve and it takes longer to get back to the higher part of the rpm curve. Take the quad to a 1/8 mile drag strip and do some runs there is a difference why do you think all the racers used them. Anyway you can get them for around $50.

This^^^^^They do more than just rev another 1000, some if not all make a different power curve, better....Doug Eichner ran them on his built 400EX an the first 416EX to win the Baja 1000 had a White Brothers CDI....no one at the track that asked me about them an then bought one was ever disapointed.

[ish416]

Steve is 100% correct, CDI boxes for an EX are a waste of money.

Yes, you may be able to rev 1000 rpm higher but, you will not be making any power at that rpm. If your quad is revving out to quickly, it is time to either change the gearing or get tires that have better traction as you most likely are spinning.

I have ran a White Bros cdi box on my EX for a few months and didn't notice anything besides it revved a little higher and never wanted to start. I think my top speed may have increased by 4 or 5 mph.

I sold the CDI and will never purchase another one again for my EX.

[Honda5]

It's not all about making power it's about where the power is and where you are at your shift points. If you don't race it's probably no big deal but when you get pulled away from in a corner and left down a straight you might want one. If you talk to any big name engine builder see what they say.

[rinconrider]

imo after having one, they are a waste of money. I wont be using any again for the 400. most of them make starting hard too. esp if you have a sub-par battery, it will start extremely bad with that. ill stick to the stocker or get the stocker modded if you really wanna have one. the xr 250 one is supposed to be the same curve but just raises the limit. dyna tek and such are ok for changing the timing but the sparks key takes care of that for alot less money.