1992 Honda cb400SF

super 400 · 1992 Honda cb400SF

My problem is that it won't go beyond 5000rpm in any gear only in neutral will it do it, now i've seen the help about deristicting the bike through the clocks and cdi, but my problems lies that i've already had the clocks changed on the bike and it still has the same problem, could it be that the cdi needs modding to? any help would be greatly appreciated.

admin

that sounds like the bike isn't running well at all.

Can you tell us any more info about the bike?

When was it last serviced?
Could be many things, extremely blocked air filter, it could only be running on 2 or 3 cylinders, or the exhaust could be blocked.

If the bike wont revv, have you checked all the fuses.
I know for a fact the bike wont revv out past 5000rpm if a particular fuse is blown.

super 400

Thanks for getting back to me. i had the bike at the mechanics this monday gone, he checked the coils the air filer and carbs and found nothing wrong, he spoke to bat motorcycles in london and they said it has a restricter fitted to it which would explain the systems really well as the bike starts fine even in the cold - tempretures and pulls really well all the way upto 5000rpm which in fifth gear is about 60mph but sounds like its missfireing after 5000rpm like its cut off 2 off the cyclinders. As i've red in one of the posts, checking to see if the bike is restricted or not involves removing the dash fuse and seeing if it reacts like mine is doing but then mine has after markert clocks on it. Is it possible that the clocks are wired wrong and its caused this problem, so that the cdi thinks its still restricted.

I've checked to see if all four cyclinders are working by checking the down pipes to see if there hot or not and everything seems ok, it has a straight through exhast and has been properly jetted so no probs there.

You mentioned that if a particular fuse is blown the bike will react like mine which fuse would this be? could it be possible that the jackass that wired the new clocks in the loom bi-passed the dash fuse, this has only just sprung to mind.

admin

thing is its the fuse that also controls the taillight, horn, and the clocks
If you pull it out then the bike wont revv, in gear.

If those are working then, i dont think its the problem.
The clocks probably havn't caused the problem.

humm so it is running nicely on all 4.
However gases do travel back through the exhaust so its normally best to check from the second you start her up.

Could be an electrical fault, but you mention bat motorcycles said it was fitted with a restrictor. What kind of restrictor is that?

super 400

apparently it had the classic speedo restriction, which has been eliminated by the custom clocks it has, but the cdi has a restriciton too whcih has not been modded, when i first had the problem i changed the cdi for one out of a CB-1 same engine hopeing it would fix the problem obiously not but then i dont know if the CB-1 has the same restricition. I've seen on ebay a unristricted cdi just for the cb400sf but i dont want to spend 100 quid if thats not the problem. Am running out of ideas

admin

yes the cb1 has the same restriction as the SF.

I wouldnt go spending loads on a cdi if its not needed.

You could try the resistor mod at the CDI end if you think it will help.
Would be worth a try, i suppose.

Ah ive had an idea, you say its got custom clocks, what happened to the block connector inside the old clocks? i think if its unplugged in runs in saftey mode. 5500rpm misfire. again the resistor mod would cure this.

super 400

i had a look at the wires that goto the cdi near the plug but i can only find the black/white and a orange/blus not a brown and blue, also no sure what Watt resistor to use will half a watt do the trick.

super 400

also could you tell me which end of the wires at the cdi to solder the resistor onto is it the wires coming from the cdi plug once cut or the wires not on the plug thanks.

admin

its supposed to a 2K OHM resistor

See the pic.
The colours are supposed to be the same, the cut wire with the red trace is supposed to be brown.
All the black wires are normally coloured. it just saved time.

http://www.rrzone.com/forums/atta...ttachmentid=8972&d=1231521809

super 400

I have looked for the brown/blue wire but i only have a orange/blue wire and black/white, is the orange/blue the one i should use?

admin

it sounds like its correct, maybe i have worse eye sight than i thought, lol.

Keep us updated.

By the way did a bat motorcycles mechanic ride the bike at all?

super 400

yeah i will try the mod this weekend and will let you know the result. Unfortunelty i live up in the nottingham area so bat motorcycles is miles away, however my mechanic rang them for confimation that it has a resistrcition on it. It all makes sense now the custom clocks where hard wired in and to be honest a mess the loom is no longer easy to find where the wires go and the plug that goes to the dash is long gone, hence when you said its running in safe mode + its always exactly 5500rpm when it missfires in every gear so fingers point to the cdi. i have a few resistors laying about but i think there 2.2k with 10% either way variance, do you know if it has to be exactly 2k or will i get away with it?

thanks

admin

to be perfectly honest with you.
I have no idea.

If you want to try another then give it a go.
If its still restricted then try another resistor.

I know that the 2K one works as its the one I used.

I think its got to be correct because it is the basic signal coming from the CDI to the clocks changes when unplugged, and the resistor fools the signal making it work normally.

super 400

i have ordered one of these will this work

http://www.rapidonline.com/Electr...arbon-composition-resistors/79895

Its the 2K one

super 400

Hi Mate

It worked my bikes runs great, thanks for all your help very much appreaciated will try and upload some pictures later of my bike.

thanks agian Very Happy

admin

wow awesome.

glad i could help.

you can enjoy that bike of yours a bit more now then! Very Happy