I have recently acquired a pre 2002 CB400SF the bike is fine and runs well before I reach 5250 RPM at which point it will miss three to five beats and then will slowly continue to climb the rev range but with no power whats so ever, in lower gears there seems to be a slight increase in power after 8000 RPM but not much.

I have had to recharge the battery twice although the alternator seems to be working as the lights will brighten once the engine is off idle, it made no difference to the problem having a fully charged battery. It does not seem to make any difference if I slowly increase the revs to 5250 RPM or get there as quick as possible its always the same, cough, cough, sputter all power gone.

A local mechanic has told me that the CB400SF has a problem with the battery and if they are ridden around with a dodgy battery this will in turn blow the CDI, could this be what has happened to this bike considering the symptoms above? The cost of a replacement CDI is quite high so I would like ideas from the forum members as if this could be the problem before purchasing one.

Any ideas suggestions or advice would be greatly appreciated.

Sounds similar to what happened to my old CBR600F2 when the CDI went bad. Ran fine in low revs and lost all power above a certain RPM. Replaced CDI and all was fine. Good luck!

Sounds similar to what happened to my old CBR600F2 when the CDI went bad. Ran fine in low revs and lost all power above a certain RPM. Replaced CDI and all was fine. Good luck!

Bigbike nailed it : replace the CDI and the battery too - a faulty CDI 'cooks' a brand new battery in a matter of hours. Let me know if you want my technician to give the bike's electrics a checkover.

if the regulater is faulty it will also give a similar problem. sounds like the reg is faulty which has caused the cdi to become faulty. So a new battery, regulater and cdi should sort it out. about 6-7thousand b max. cb400 spares are plentiful at least.

Ditto above as soon as I read it the prime culprit would be CDI..

Not unusual to find CDI's from wrong model and even make bodged in, but less so for the CB400 as its really well supplied for parts.

Thank you all for the swift replies, it looks like I will be hunting around for a new CDI and battery. I think I will get the multimeter out to check the regulator rectifier unit before I replace it. Thanks for the offer of the use of your technician Ricochet but unless he is anywhere near Nan it would be difficult for me to get the bike to him.

I wonder if my local Honda dealer would be able to get the CDI for me or I will have to go to my local supplier which is located 120k away, it's a nice ride to get there though

Thanks to all once again

Buckaroo,

Before you go spunking big $$$ on a CDI, check the air filter. I run a fleet of SuperFours and have seen EXACTLY the same symptoms from a dodgy airfilter amongst other things.

It could be that someone has bodged a home made filter with foam which looks great but once the revs rise, the foam kind of collapses in on itself restricting airflow. Easy check - take the sucker out and go for a run.

Secondly, check the cam timing - being out one tooth can have the same effect.

Lastly, check fuel flow - run with the petrol cap open and see if that makes a difference. You may have a blocked vent or something similar. A trick here is to remove the drain screws from the base of each carb float bowl and attach an airline to the hose that comes from the fuel petcock. Give it a good blast to dislodge anyt potential blockages in the carbs.

Just throwing these ideas in here as cheaper and easier checks before shelling out for a CDI.

Cheers,

Pikey.