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I have a 20 year old Kawasaki ZZR600. She was running fine in December. I didn't ride her for a few weeks in January. Left the battery on maintenance trickle charge.

A few weeks or so ago I fired her up again. She started fine, absolutely normal. I had the choke out as normal for the slight cold. With the choke out she idles at 3,000 - 5,000 revs depending upon exactly how far out.

Once she's warm she idles just fine with the choke in, at 500 - 1,000 rpm.

But if I open the throttle to rev the engine, there's a very short burst of revs, for maybe half a second, then the engine cuts out. This happens with both the choke in and out.

Assuming nothing has been done with or to the fuel lines and carbs since she was running fine in December, what possible causes could result in this ?


UPDATE:

I write this here as there simply isn't enough room in the comments. I have marked the Seafoam answer as correct, although whether water had anything to do with it I didn't ever find out.

My attempt to apply Seafoam was pretty amateurish, but it still seems to have worked.

The videos I watched varied in their instruction but they all seemed to include getting pure Seafoam directly into the carbs. I struggled to do this. Imagine some comedy moments trying to get a funnel into the fuel pipe, and pouring Seafoam into the funnel while running the engine to suck it through, and then cutting out before any Seafoam has got in there.

In the end, I drained the tank and then filled it with approx a litre of petrol / Seafoam mix - very strongly Seafoam, maybe eighth / quarter of a litre Seafoam. Then I ran the engine for 30 mins, left it a day, ran it 30 mins the next day, waited another day, etc, for 3 days or so.

Whilst running the engine I played with the throttle, moving it micro-amounts looking for the point where it caused the engine to cut out. I experimented with having the choke open to keep the engine running, whilst opening the throttle enough to dip the revs without cutting out.

Eventually, after a couple of days, I found the "bite" on the throttle moving, so that I was able to open the throttle more and more before the engine would cut.

She appears to be running pretty well now. I intend to fill the tank up (she holds 18 litres) and empty the rest of the Seafoam in, and ride her around for a bit, see how it goes.

I probably should still get the carbs professionally cleaned (or get myself properly equipped and on a maintenance course).

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Are any of the jets clogged? maybe running some carb cleaner through them would help. Have you checked for water in the fuel? –  Mauro Feb 24 at 9:51
    
We had a very wet January, so if there was something dodgy about the fuel cap, then maybe water did get in. Is there a way to tell for sure, or should I just empty and re-fill the tank anyway? –  Stewart Feb 24 at 15:07
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You may be able to see water in the fuel filter if its clear and if you can get to it easily. –  Mauro Feb 24 at 16:27
    
Been working on getting to the fuel filter, but it's not been obvious, even with the Haynes Manual to hand, exactly where it is ... I'll solve that and let you know –  Stewart Mar 8 at 10:52
    
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up vote 1 down vote accepted

I had the same problem with my Katana 600. Ran some Seafoam through it and it got better, presumably cleaned up any deposits from gas sitting in the carbs too long.

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This stuff? seafoamsales.com –  Stewart Feb 25 at 16:21
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Yep. seafoamsales.com/sea-foam-motor-treatment specifically. I used it as a fuel system additive (per the instructions). Didn't magically fix it immediately, but after a couple sessions of running it, it got better so that on the third day I got it out the problem was gone. YMMV of course, since we're not 100% sure that's your problem. Relatively inexpensive and easy thing to try though. –  Brian Knoblauch Feb 25 at 16:45
    
Seafoam in the post; been watching videos on how to use it. Will let you know how it goes ... –  Stewart Mar 8 at 10:52
    
See update I added to the answer to describe how it turned out :-) –  Stewart Mar 14 at 13:47
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