ZXR 750 running issues. Carb icing? Fueling?

[Coxyzxr]

Back again! With definite running issues on the zxr guys. Possibly fueling.

Been running ok but lately (Unable to confidently attribute it to the cold due to not remembering) it's been a real pig in the low revs and sometimes the higher.

Feels like it's jetted really badly on the pilots/rich floatboals and such as from 2k to about 5 it's stutters and bogs like it's too rich.

Occasionally it starts running on only 2 or three cylinders.
If you stop at lights it will stall and pulling away's ... interesting.

I don't think it's electrics as when you get past 6k it's gets better, still occasionally surges and such but much better than below 6.

Likewise I feel it may not be carb icing as as far as I know carb icing gets worse the faster / more revs you go. (I had it a few years back and faster I went the more the bike stalle)

Making town driving a misery.

I've:
Checked air filter.
Drained float bowls (clean as a whistle)
wd'd spark plug caps and checked all the connections.
Had airbox off and checked for leaks and re-sealed using rubber grease just in case.
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**WAS FITTED "WRONG WAY ROUND" !** CANT ACCOUNT FOR THE STUPID !

[Kickstart]

Hi

Carb icing would probably be less noticeable at high speed for a while, just making it far worse at low speed in the process. Would also likely solve itself if you sat at low speed for a while (ie, stuck in traffic as you don't dare filter with such a dodgy throttle).

Are the carbs standard? Dynojet kit? K&N? Aftermarket pipe?

All the best

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

[Coxyzxr]

[Kickstart]

Hi

Seems odd. Would expect the colder weather to result in the bike running leaner rather than richer.

Could be worth getting it a run on a dyno to check the mixture. Possible that the 4>2>1 is behaving very differently to the stock system and needs a very different shape set of needles, with you getting away with it in warmer weather. Lean at some rpm and rich at others. However I would be surprised if it made that much difference.

One reason I asked about a Dynojet kit is that the needles used in some aftermarket kits are renowned for increasing wear on the atomiser tubes, making the bike run quite a bit richer at some revs.

To count out carb icing lob some suitable fuel additive in for a tank (and try a few tanks with and without it). To be honest I doubt is will make any difference but at least it is an easy thing to count out this way.

All the best

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

[Coxyzxr]

[Kickstart]

[Coxyzxr]

[Kickstart]

Hi

To be honest not sure. Possible, but also possible the opposite is true. Suspect it would be down to the particular fuel blend.

All the best

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

[hmmmnz]

when was the last time you did the valve clearances??
i had no end of what i thought were fuelling problems,
which in fact turned out to be the clearances,
give it a go, and see if anything is out
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I kick arse for the lord
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[Coxyzxr]

[0ddball]

if it ran fine before im 99% sure its carb icing. Sounds the same as my symptoms on the same bike and i was getting it even before it started getting frosty about 2 months ago.

Never bothered to try curing it though as i bought a cheap car for the winter.

[Kickstart]

Hi

Make sure the filters for the carb heaters are clear.

All the best

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

[Coxyzxr]

[Kickstart]

Hi

Yes, that is what I meant and there is meant to be a filter in the pipes to the carbs. They have a reputation for getting blocked quickly on Kwaks.

All the best

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

[temeluchus]

The only other thing that springs to mind is a leaky float valve on one or two of the carbs. This would cause rough running similar to what is described-ie dropping cylinders and strong whiff of petrol, but clears at higher RPM.

Can actually be mildly beneficial in winter as the slight leak helps cold starting X-D

Carb icing is still more likely, but its worth a look.
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[Barry_M2]

So, from what I gather, it runs ok when cold and starts to play up when the motor warms up a little? Runs on 3 (or 2), stalling... etc..

Initially I'd say fueling, but I could also be one of the coils playing up. When you had the float bowls off, did you remove the jets and clean them?

If it were me, I'd get it warmed up until it starts to missfire, see what cylinder it is and swap the plugs round to see if the problem follows the plug. If not, clean out the carb jets. If thats not it, see if you can find a spare coil and give that a go.

If its only running crap at low rpm, I'd suspect pilot jets.
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CBR1000 RR4 - For the track.
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[Coxyzxr]

[base]

i used to own a H2 i had similar symptoms to the ones you described and it was a sticking carb,