Help!!! Race bike is sick

scottiel · Trackday Trickster Joined: 07 Feb 2005 Karma :

Help My race bike is sick.

It is a steel frame CBR600,

Symptoms: When the bike is in 1st or 2nd gear it revs out and pulls no problems. As soon as you click into 3rd it starts spluttering at about 5000 rpm and only revs out to about 10000 rpm and as you click up the gears it gets worse.

What we have done so far:

Checked the Carbs, needles,jets,floats, etc. they are all fine.
There was some water in the petrol but that has been flushed.

Air Filter is ok also.

Could it be an electrical fault.

The strange thing is when the bike is on the stands it revs out 100% in all gears, it only gives problems under load (no Iam not a fat bastard, before anyone asks).

Please Help. Crying or Very sad

Cheers

Scottie

Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

Hi

While you say that it works fine on the paddock stand and fine in the lower gears when riding I would suspect that the problem is something that is getting worse with time. Bet that if you thrashed it through first and second then spent ages trying in third then tried 2nd again it would be dodgy in that gear as well.

First guess would be a blocked fuel tank breather. A partial blockage will allow some fuel to flow, but not enough to keep up with what the engine requires under power. This way as you use fuel the level in the float bowl gets lower and causes problems.

All the best

Keith
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EuropeanNC30R... · Gay Hairdresser Joined: 20 Jun 2002 Karma :

Is your fuel tap vacuum operated by any chance? I had similar problems (but not as bad) when the vacuum hose on my nc30 became perished. It meant at higher speeds the carbs couldn't suck in enough fuel.

G · The Voice of Reason Joined: 02 Feb 2002 Karma :

Make sure the carbs are 100% attached properly?

It seems /some/ of the problems I've had were because I thought they were fine but when everything was fully connected there was a slight leak somewhere.

scottiel · Trackday Trickster Joined: 07 Feb 2005 Karma :

Cheers guys I will try some of your suggestions out tonight.

Just to let you know as well when you are flat out in second and back of slightly, the bike misfires, then picks up again as you put the power down again.

I was out on Saturday at a race meet and in 5th you couldnt get passed about 6-7000 rpm but when you dropped to 4th it picked up on to the limiter for a split second then died again down to about 10000rpm. It felt like it was running on 3 cylinders.
Pain in the ass.

G · The Voice of Reason Joined: 02 Feb 2002 Karma :

That does sound very like some of the problems I was having.

I couldn't test the bike in the padock because I couldn't go fast enough for the effect to show up.
In higher gears I was getting a kind of 'surging' at points.

Mark hill took me through replcaing the carbs - making me undo every clip etc (well, undo more than I was at the time).

It seemed that I just wasn't making quite a good enough seal around the carbs.

scottiel · Trackday Trickster Joined: 07 Feb 2005 Karma :

Hi Guys

It seems the fuel pump is the culprit, went out tonight turned bike on and fuel pump keeps running, as in when ignition is on but not turning over, the fuel pump keeps winding on it normal stops after a few second, iam sure you all know what I mean.

Cheers

Scottie

G · The Voice of Reason Joined: 02 Feb 2002 Karma :

I was getting this when I had dirty carbs.

It was actually that the carbs were constantly pouring fuel into the engine!

This also seemed to cause some of the symptons you describe; though I think I had several problems at once at points.

So I'd get your airbox off and have a look down the carbs when it's doing this; if fuel is coming out then the fuel pump is just doing it's job, it's the carbs that are at fault.

VFR400UK · Scooby Slapper Joined: 29 Jun 2004 Karma :

Spluttering and backfiring could be cause my carbs not seated or sealing properly.
I had a similar problem with my bike a while ago, it turned out to be that the choke was sticking on meaning it ran allright when cold but gradually got worse with time and splutters and backfired in the upper gears.

proximity · Crazy Courier Joined: 08 Oct 2004 Karma :

Before you go replacing the fuel pump, its more likely that there is just no or little fuel getting to the pump, so its clicking away trying to fill the carbs.

Best off checking the flow into the pump first.
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2004 Aprilia Tuono

the grim reaper · World Chat Champion Joined: 29 Jun 2005 Karma :

The weird thing is that this doesn't happen in the lower gears, I'd still suspect something else. The bike doesn't use any more fuel at 10000 revs in first than it does at 10000 revs in fifth, just the road speed differs.

It also doesn't make sense that it could be electrical as it would affect all the gears again. I'll have a think on this one and see what I can come up with. Don't hold your breath though Very Happy

Cheers

Grim
____________________
Adverts don't always work: Remember that advert, where the army are running across the desert and they have a wounded man on a stretcher. They get to a ravine, the bridge is down and a caption pops up that says, 'What are you thinking?'. I don't know about you but I was thinking, 'Christ, I'm glad I'm not in the f***ing army'.

proximity · Crazy Courier Joined: 08 Oct 2004 Karma :

Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

Hi

Could be the fuel pump. Could also be the fuel filter (especially if it is before the pump).

While the engine on full throttle at 10000rpm uses no more fuel in 6th than in 1st, by the time you get to 10000rpm in 6th you have used a fair bit of fuel so will have run down the amount in the float bowls.

I agree that you need to check the fuel flow to the carbs, but also from the carbs.

Normally carbed bikes use pumps that cut off when there is too much pressure. As such if the pump is running there is unlikely to be a blockage after the carbs.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

Big Pete · Spanner Monkey Joined: 18 Jul 2004 Karma :

I had the same symptoms with my other halfs cbr4, after much checking of carbs filters etc it turned out to be a dying CDi module Mad

. If you can borrow one to try it would be worth it as it only takes about 5 minutes to change over the units.

you can get replacements for a cbr6 from here

https://www.cdiunits.co.uk/

HTH
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Trust me, I`m an engineer
GarageOfPower.co.uk

the grim reaper · World Chat Champion Joined: 29 Jun 2005 Karma :

OK, so the bike will use more fuel (by a *tiny* amount) due to wind resistance but that's all.

I reckon it will be the CDI unit, that is the only part of the bike that even cares what gear it's in. It's odd that the bike is fine on the stand though as an electrical fault shouldn't care whether the bike is on the road or not.

You haven't fitted aftermarket VFR clocks with a speed limiter have you? Very Happy

Cheers

Grim
____________________
Adverts don't always work: Remember that advert, where the army are running across the desert and they have a wounded man on a stretcher. They get to a ravine, the bridge is down and a caption pops up that says, 'What are you thinking?'. I don't know about you but I was thinking, 'Christ, I'm glad I'm not in the f***ing army'.

proximity · Crazy Courier Joined: 08 Oct 2004 Karma :

Let me know how it goes, as it sounds similar to my problem which STILL isnt fixed after months Evil or Very Mad

I've been through everything including a CDI.

Try running with the fuel cap open, it doesnt cost you anything and its something else ruled out incase of a vacuum in there.
____________________
2004 Aprilia Tuono

scottiel · Trackday Trickster Joined: 07 Feb 2005 Karma :

HI guys, got it sorted.

One of the air pipes had come loose.
Had a faulty fuel pump as well, but it was the air pipe causing the problem.

Having no bloody luck at all with this bike in the last 3 race meetings.

Also got the shocks looked at because the adjusters where stuck.
Was out at a race meeting yeaterday and the front end was all over the place.Every time I came into a corner the bike tried to push me wide and as I tried to turn it back it felt like it was about to wash away, infact twice I had to dig the knee in to flick the bike back up.

I have another meeting next weekend so looks like it will be busy weekend again sort damn suspension out.

Pain in the arse cause the bike is really fast down the straights now I have all the power back.

proximity · Crazy Courier Joined: 08 Oct 2004 Karma :

What air pipe?
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2004 Aprilia Tuono

scottiel · Trackday Trickster Joined: 07 Feb 2005 Karma :

There are two pipes which go onto the carbs under the airbox.The left handside one had come loose.

proximity · Crazy Courier Joined: 08 Oct 2004 Karma :

Im a bit lost here. Do you mean the actual air to the venturi or some other pipe, im not sure why else air would go to a carb.
My carbs look like this, the two long pipes are overflow pipes i think, the thing i circled may be something to do with air but there is no pipe for it. Its probably specific to your bike but i thought i would check anyway.
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2004 Aprilia Tuono

scottiel · Trackday Trickster Joined: 07 Feb 2005 Karma :

The bit you circled looks like it except mine has a longer pipe which joins on to the other one and then into another pipe. I will photocopy the manual tomorrow it will probably show you better what you mean.

If you take of the tank there is a thick pipe and a thin pie running round the air box. The thin one has 2 branches coming off it going onto what you circled.

My bike is a 93 engine in a 95 frame but the carbs and air box are from a 97 as far as I know, It is a bitsa as we call it.