zxr 750 choke issue

[RickTaff]

Hopefully some light can be shed on my issue

I have a zxr750 J1 1991 model, and on a cold start with full choke the idle RPM shoots to about 6-7k, and i just cannot seem to be able to even partially take the choke off at all, without it wanting to die. Revving that high it is horrendously loud! And it always has to be choke fully on for it to start, cant give it half, or quarter for example.

I understand you have to let the bike warm up and then it should start behaving correctly, but i cannot leave it on full choke at 6-7k for 10-15 mins, surely to god

Tried slackening the throttle cable, removing throttle cable off carb linkage thinking maybe it was holding the throttle slightly open, no luck.

Slackened off choke cable itself, too.

Just cannot work out whether this is simply common for ZXR750's, or whether it sounds more likely to be shit in the carb jets which needs cleaning out (which is tomorrows "to do" job), or maybe they're just out of sync? Totally at a loss.

[Polarbear]

I don't know that specific bike but every bike I have owned with a manual choke, and I have owned many, has been totally controllable revs wise when warming up on the choke so I would certainly surmise something is wrong.

If, when warm and choke off the bike runs perfectly well I would guess I would be checking the choke mechanism, be it butterfly's, cable or whatever.

So carbs off and clean. Check operation of choke on all four carbs and cable. Check no rubbers are split or gone hard and leaking. Has the bike been standing for a while?

I'm sure someone with specific knowledge of that model will be along at some time with better information.
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Triumph Trophy Launch Edition

[Easy-X]

Classic '90s racing Does the J1 have the CV or flat-slide carbs? And is it okay after it's warmed up?
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Royal Enfield Continental GT 535, Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[jaffa90]

Sounds like carbs need servicing as said (fuel level & cv i think), also do you use a fuel tap ?

[Kawasaki Jimbo]

I’d look for an air leak at the airbox seal or the carb rubbers.

[RickTaff]

[RickTaff]

[RickTaff]

[Easy-X]

Having the carbs off to clean sounds like a plan, don't forget to check the rubber diaphragms for damage

Given that this bike doesn't have a fuel pump (and you're taking the carbs off anyway) it wouldn't hurt to take a look at the fuel flow. While the filter doesn't look clogged it's good for peace of mind to see the petrol pissing out
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Royal Enfield Continental GT 535, Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[Robby]

Wasn't this a standard thing on 90s Kawasakis, choke was either on or off. Vague memories of ZXR400s at box hill sitting there revving their tits off on start up.

[RickTaff]

[RickTaff]

I think i may have narrowed it down slightly

Just had a thought that when i had airbox off yesterday, i noticed my vacuum pipes to sync the carbs are already attached to the cylinder, and just sat underneath the airbox ready..... however

Each pipe has like a white plastic sticking out the end which the vacuum guage pipe attaches to, and whoever sync'd the bike last, or worked on it prior to my ownership, has not put the rubber caps back onto the white plastic ends. So i assume, obviously, it'll suck air in through there

Touch wood, covering those up with some makeshift stop gap until i can replace the rubber caps, will help in some way. Even if i got to really bodge it and wrap it in insulation tape just to test.

[A100man]

[Easy-X]