CBR600 hesitating

[Ichy]

I've noticed that my CBR600fy, 2000 model year, is sort of misfiring / hesitating / jerking at between tickover and about 2500 rpm. Certainly above 3k its running fine, except for a few vibes. Bike is fitted with carbs, standard airbox and a scorpion race can. No idea on the service history.

My thoughts at the moment are carb balance, plugs, and checking the mixture screw. Anyone got any other pointers or have heard of this problem before?

Forgot to mention the idle is hunting a little bit too, about +-100 rpm.
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[baldy]

Have the carbs been balanced recently?
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[Noxious89123]

[CBA]

just a thought, check the cooling system, make sure the rad is full to the top and there are no airlocks, could be that the level is low and the sender is'nt fully dipped in the water.

might not be a bad Idea to renew the coolant even if nothing seems wrong, you said you were unsure of the history.

[baldy]

Why would the coolant effect the feuling?
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One day i will rule the world, just not today.

[Ichy]

Baldy, as said I know nothing of the service history although it is fairly evident that it hasn't been neglected based on fluid colour and pads / discs / sprocket / chain condition. I personally think the pilot jets needs cleaning since the bike has stood for the good part of a year. I did about 200 miles in the last two days and its all running good other than the obvious. I'll strip it down today. Pity you can't get seafoam in the UK.


CBA, either you have some very indepth knowledge of Honda engineering or your in the wrong thread. I have my own opinion on the answer to that one.
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[Ichy]

Synched the carbs and its still the same.

Realised today that it doesn't do it when the bike is cold, I'm assuming that rules out blocked jets?


Sooooo, I now believe that its just a mixture thing, possibly due to the race can. I shall play.
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[mutley247]

It may be a long shot, but is the can new?
was the bike running fine before or synce you have put the new can on, (If u fitted it)

It is a long shot i know, but the size and lenght of the can is part of the fine tunning, i cant remember how it works, but putting a longer or shorter can on could effect the draw of the exauset gasses.
It is just a thought,

(Sorry about spelling, it's late)
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[Noxious89123]

How noticable is it that the revs aren't stable when ticking over? Does the needle wander up and own the tacho, or does it jump up and own a little?

The tacho needle on my bike wiggles up and down a little at tickover, as if it's ever so slightly lumpy. Just figure it was a "charactaristic". Can't remember if it's always done it or not.

I have a standard can fitted to non-standard aftermarket stainless pipes. They are almost identical to stock though, cross over pipes and all.
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'06 Honda CBR125RW-6 ~ '00 Honda CBR600F-Y ~ '07 Honda CBR600RR-7 ~ Bikeless
'53 Ford Ka 1.3 ~ '03 Vauxhall Astra SRi 1.8 ~ '52 Vauxhall Astra SRi 2.2 ~ '53 Vauxhall Astra GSi

[kungfupoodle]

Worn out needle jets? If they're not still perfectly round it could be running too rich in that part of the rev range.

Take the carb tops off and the slides out and have a look down

It doesn't have to be much...

[Noxious89123]

How do they get worn? Only fuel is going through them, no?
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'06 Honda CBR125RW-6 ~ '00 Honda CBR600F-Y ~ '07 Honda CBR600RR-7 ~ Bikeless
'53 Ford Ka 1.3 ~ '03 Vauxhall Astra SRi 1.8 ~ '52 Vauxhall Astra SRi 2.2 ~ '53 Vauxhall Astra GSi

[kungfupoodle]

[Noxious89123]

I guess, but it's not like they're carrying alot of load or moving really really fast...
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'06 Honda CBR125RW-6 ~ '00 Honda CBR600F-Y ~ '07 Honda CBR600RR-7 ~ Bikeless
'53 Ford Ka 1.3 ~ '03 Vauxhall Astra SRi 1.8 ~ '52 Vauxhall Astra SRi 2.2 ~ '53 Vauxhall Astra GSi

[Ichy]

[tshort2007]

I had a similar prob on my 125 stroker. Spent ages esetting carb, checkin electrics etc.

Found out the needle jet was worn, and the needle was bleeding fuel into the mix, makin it too rich.

New needle jet cured it and low end throttle reponse is much much sharper.

[kungfupoodle]

Ichy, it does sound like needle jet wear. It is (probably) the first thing that wears out on a carb.

As soon as you come off idle you're onto the needle jet - and even at idle it will have some effect.

If you have circlips at the top of the needle you could try moving them up a notch towards the top of the needle. This will help to reduce the amount of fuel coming through the jet if it is worn.

I had to do this on my GSXR as the needle jets were press fit into the carb and couldn't be replaced (at least not by me )

[Blackwolf]

[Ichy]

Blackwolf, looks lke yours is even the same colour

I think it is because of the can that it is doing it. It just needs the carbs tweaking. In fact I could probably test that theory very quickly since I have the original can. Well as quickly as I do anything so that means tomorrow.
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[Noxious89123]

Changing the can is only 3 bolts, should take about 2 minutes!
____________________
'06 Honda CBR125RW-6 ~ '00 Honda CBR600F-Y ~ '07 Honda CBR600RR-7 ~ Bikeless
'53 Ford Ka 1.3 ~ '03 Vauxhall Astra SRi 1.8 ~ '52 Vauxhall Astra SRi 2.2 ~ '53 Vauxhall Astra GSi

[Blackwolf]

[Ichy]

I know it doesn't take long, I'm just lazy!

What interests me is that the symptoms indicate a rich condition. I'm surprised that a race can would do that. The ovality of the emulsion tube is not unlikely.

Anyway, changed the cans over and it was pretty much the same, maybe a fraction better, so I'm assuming that rules that idea out. I went to my mates garage and he gave me a bottle of something called Forte advanced formula gas treatment and told me not to stick it all in at once. I went for a little ride, maybe 12 miles, and while it may be a bit of snake oil it did seem to get better. It was certainly better riding around at 30 and it was possible to pull 6th gear from 2k without my eyeballs being shaken out. I'm still going to have a play with the carbs tomorrow, assuming I can find the mixture screw and adjust it, but it might be worth just going for a long ride with this stuff in it. It'll be interesting to stick the scorpion can back on and see if it feels the same.
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[Raf]

I will be interested in hearing your results as mine has been experiencing the same problem. I can tell you its not the plugs as i have just replaced mine recently and its still the same. I have also used a fuel additive to clean the carbs. I've not been through an entire tank yet so i cannot tell you if it has worked.

Im tempted to strip the carbs down some point this week but as i use the bike everyday i will have to do it when i can find the time.

Keep us informed.
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CBR1100xx - BMW K1100 - BMW K100 - Triumph Sprint ST 955i - Suzuki GSX-R 600 - Suzuki DR 350 - Yamaha XV 750 - Honda CBR 600 FM - Yamaha XT 600 - Yamaha Rs 200 - Honda NSR 125

[Ichy]

Will do. If time allows I will play about with the carbs this weekend. At worst its going on a dyno next week. I know the guy and trust his judgement when it comes to fuelling so it might be interesting anyway. I accept its the easy way out but he has suggested fitting a dynojet kit at a cost of £130 including setting up.
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[CBA]

[Ichy]