admittedly not an FZR400 (it's my FZ750), but you lot have more bikes apart than anyone in the history of the world ever.

Thus you are bound to take 1 look at this youtube i filmed just this evening and will be able to tell me what the f**k is going on.

Case history - FZ750 bought after being laid up for 3 years (dry carbs - proper stored) perfect runner when it was laid up, after recommissioning it had developed a hesitancy in the midrange which required part throttle to be applied to get through it before it came clean and ran to the redline.

New fuel pump was fitted - didn't do anything.

I took the carbs apart, they were clean and free from gunk. having put the things back together, I now discover this fuel spraying trait - is this float height, and if it is, is it behind the poor running? - bear in mind the bike idles, goes flat out and tours just fine, it's just hard acceleration makes it fluff until you back off in the midrange and then open up the other side. Things I've read lately make me think it might be the coils breaking up, and not the carbs at all.

The fuel pump is cycling in this film because I had a very small bottle of petrol attached to the fuel line and it emptied part way through testing it.

http://www.youtube.com/watch?v=BjJsUv-fCVw

before I spend another minute messing around with it, I'd love some clues as to whats actually going on!

toosmooth

I had the same throttle response thing on my fz750 and it was a float needle not seating, so carb was overflowing. If you run the fuel pump ans petrol pisses out then you've got your cuplrit (flick the iggy or kill switch off and on for another 5 seconds of pump running)

Good call - how can you tell if the buggers are gonna seat properly though? - I've got the carbs apart right now and everything looks as hunky dory as it should do.

I've run out of talent and experience.

One more strip, One more clean, tweak the float height down a tad, just a tad (they all seemed to be flooding, only one was overflowing with vigour) and thats it. next stop professional help.

wish me luck!

toosmooth

update.

carbs refitted, no overflowing. obviously won't start because of the 43 gallons of juice I have already allowed to pour neatly into the engine tonight.

hopefully tomorrow, it starts again!

It can be hit & miss sometimes. I use clean kitchen roll to clean the rubber bit and an air blast gun for all of the jets, seats, etc.

Sometimes the pivot or the tag that presses the valve needle is misalligned, which causes it to jam.

Hope it works

started on the button the next morning.

if it's not one thing it's another.

the next problem - the airbox rubbers wouldnt go back on, had to run it up the road with the airbox kinda bodged on (it fell off, changing induction noise and performance fairly instantly!)

If I buy a second hand airbox, no guarantees that it wont be just as shyte as this one. This bike has had an easy life and is in good nick. I might just take the rubbers I've got and dremel the bastards back to the right size, for the reason they wont fit is that they simply are too small for the venturi.

Anyway, it ran, it ran crisply off the bottom, but with the airbox issue I couldnt tell if it was fluffing because the float heights are now too low when I open it up, or because it had an airbox hanging off!

Deep joy, but hell, it's progress, and I tell you what - it's a bloody peach to ride!

toosmooth

buy some new rubbers. If they're anything like the 1wg ones it's simply easier to replace them

I agree with evil on this one.

If it's a one-off, use a hair drier to warm them up and soften them. But it's a pain in the ar$s doing that every time.