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Discussion Starter · #1 ·
My ZXR750R (K) was laid up for a couple of years following a problem and is now nearing completion. I have cleaned and rebuilt the flatslides using an ultrasound bath, set the float height and re-sealed the inlet rubbers. The bike will fire up easily and run (and respond ) well on choke, but as soon as it warms up and the choke is off, the bike will either go straight to 5,000 rpm or settle at tick over where the slightest movement of the throttle kills the engine or sends the rpm upto 5,000 again. Sounds like an air leak - but how, the inlet rubbers are not split and are hylomar'd to the head. All attempts at balancing fail because i think the fault is more fundamental than that.
The pilot screws are set to 1 and 5/8th's out.
I have also checked the wiring to the fuel pump and solenoid (Does the fuel pump only operate when the starter is engaged ?).
I noted that the needle valves are set at differing clips for the outside and the inside pots, carbs 1 and 4 are 4th groove from top, carbs 2 and 3 are 6th groove from top (these have not been adjusted since it last ran well).

If anyone has any advice i would appreciate it as im pulling what hair i have left out !

Kwackernut (Dying to get that manic grin that comes from ZXR ownership back).
 

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Super Duper Mod Man
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10,479 Posts
Sounds like your pilot jets got clogged up when it was laid up. I know you say you cleaned the carbs, but pilot jets are awfully small and need to be looked at. Since it idles and runs at 5000 rpm +, I'd say the pilot jets are the culprit.
 

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The Toad
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Make sure that the choke is completely off. Many of those bikes had mixture enrichening curcuits and if the choke lever on the carb bank is not completely closed the bike will run very strangely. In the past I have had to rig a spring on the actuating lever to make sure it stays closed. I'm taking about the choke lever on the carbs, not the choke control on the handlebar.
 

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Discussion Starter · #4 ·
ZXR750R Carbs

Sounds like your pilot jets got clogged up when it was laid up. I know you say you cleaned the carbs, but pilot jets are awfully small and need to be looked at. Since it idles and runs at 5000 rpm +, I'd say the pilot jets are the culprit.
Thanks longride. You may well be right, although i cleaned them in the ultrasound bath, the drilling for the pilot jet is very small and could easily be blocked. Hopefully the bath can dislodge the fuel varnish, if it can't, im not sure what else to do to clear it - im loathed to stick wire in the hole. Kwackernut.
 

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The Toad
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Thanks longride. You may well be right, although i cleaned them in the ultrasound bath, the drilling for the pilot jet is very small and could easily be blocked. Hopefully the bath can dislodge the fuel varnish, if it can't, im not sure what else to do to clear it - im loathed to stick wire in the hole. Kwackernut.
You can use soft copper wire carefully. Works pretty good.
 

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Discussion Starter · #6 ·
ZXR750R Carbs

Make sure that the choke is completely off. Many of those bikes had mixture enrichening curcuits and if the choke lever on the carb bank is not completely closed the bike will run very strangely. In the past I have had to rig a spring on the actuating lever to make sure it stays closed. I'm taking about the choke lever on the carbs, not the choke control on the handlebar.
Cheers Seruzawa. I have just been and checked the choke lever, the carbs have a spring return on them, the linkage is smooth and the lever returns to fully off when selected on the choke control. Thanks for the advice. Kwackernut.
 
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