Hi All,

I've just bought a 1988 CBR400 NC23 race bike, it has supposedly been set up by an ex-race technician but who knows?! Anyway, having only had it for a week or two I've not had much time with it but it really struggles to rev over 7-8k in neutral. I haven't had chance to ride it but surely it should rev ok stood still? I'm by no means an expert on bikes so this is where I'd like some help please.

Here is a list of things that it has had done so that you have more of an idea of what it is;

Full titanium 4-2-1 headers with scorpion can
Gas flowed cylinder head
Stage 2 carbs with 112 dynojet main jets (Still has standard air box and filter)
Lightened and balanced bottom end

That is about it for engine work, it has no ram air system, it has a high volume radiator and everything else is completely none engine related.

I've tried smaller 105 jets and also bigger 125 jets but neither made much of a difference. The 105's were really bad and just didn't want to go at all and the 125's did manage to get around to 14k but, with a lot of persuasion and popping, flames etc.

Today I've tried keeping the 125's in but restricting air flow by very crudely taping up some of the inlet holes on the air box. It revved perfectly to around 10-10.5k and then all four cylinders just died and didnt want to go any further.

Does anybody have any ideas what it could be or have you had the same problem?

Any help would be greatly appreciated!

Thanks.

Welcome for starters.

Second - some more bike details and pics please. Most of the guys on here have a good idea about the bike that are out there in circulation.

So..stop revving it's arse off in neutral - the bikes don't like it.

You need to ride it, or dyno it to get a proper view on the fuelling. simple as that. Twatting it full throttle when cool, or not warm enough and without any load is a recipe ofr dodgy ideas and pissed off neighbours.

This is the place that can sort it...

Ok, what other information should I post about it? And how do I upload pictures of it?

Cheers

there is a sticky thread on the pics - have a look in the newbies / general sections.

ref more data well - what do you know about the bike?

Has it always done it? when did it start? is it all gears? only when on a stand? etc etc

Howard400 wrote:Anyway, having only had it for a week or two I've not had much time with it but it really struggles to rev over 7-8k in neutral. I haven't had chance to ride it but surely it should rev ok stood still?

Not always, particularly if you haven't warmed it up properly (up to 10 minutes of running).

Wait until you ride it to see if there's a problem, you're possibly just creating more!

Ok, well apart from what I've already said other modifications are just cosmetic/none engine related. I know that the bike has mainly been stood for around 3 years since it was last raced in a 400 racing class in 2009/10 (not sure which one). It has been used for the odd track day since but not for the past 12 months. It obviously didn't do this while it was being raced/tracked. I unfortunately don't have a daytime mot or any local land to ride it so all that I know is what it does in neutral and while it's on a paddock stand, it seems to make no difference whether just on a rear stand or on rear and front stand so nothing to do with angles. I know I should really ride it but I plan on taking it to Cadwell for a track day on 22nd March and don't really want to waste half of the day setting it up

P.S. I'll try to upload some pics soon

http://s1299.beta.photobucket.com/user/ ... C23%20Pics

Here is a link to pictures

If its been standing for 3 years, give the carbs a good clean and treat it to a new set of plugs, or at least clean the ones in it.

Sorry, I should have said earlier. The carbs are very clean already, I've taken the jets out and they are all clear. I've put a new set of spark plugs in as the old set were black! The last thing I've tried is checking the diaphragms and needles, they were all ok too. Tried putting an extra shim on needles but that didn't help either!

I think you're worried about nothing.

Take it to the track, see how it goes. Bring enough tools and jets with you to change the carb settings at the track if need be, it doesn't take long.

At the moment you're just guessing.