ok guys --brains trust time here--zxr400 probs

[FROSTY:Me]

Im having a bit of a problem getting my zxr400 to do its thing propperly.
Its running very rough and gutless up to about 6000rpm then it clears out and goes fine.
I've spoken to the previous owner who tells me the following.
It was a stock bike and was running fine and well right through the rev range. he fitted a foam filter air box and an after market pipe.Still running fine. He removed the speedo and fitted a little box to fool the bike into thinking it was in 5th gear when in top--still running fine.
He took it to a mechanic-I wont say who and he basicly butchered the carbs.
He then took it to another mechanic he reset and rebuilt the carbs.
Still It wouldnt run propperly down low.
Ive checked compression--fine -one cam had a dodgy lobe so I replaced that. Ive cleaned the carbs and checked them over and they seem to be fine
the jets are the correct size- um factory mains are 100 and ive got 102 in there.
I was going to drop the needles one notch but it has non adjustable needles so i can only raise em.
Someone has suggested I should try refitting the speedo to see if it will
solve the problem down low but I thought the wizz box would fix that.
Any Ideas /suggestions no matter how stupid they might seem greatly apreciated- this is driving me nuts

[riffer]

what do the plugs look like? This could indicate how its running.

and have you checked the fuel lines for cracks, or the fuel filter?

Possibly also the ignitor box has issues too...

[pete376403]

It's a brave backyard mechanic (not Xj, the person who shagged the carbs) who thinks he knows more about a motor than the factory that designed it.

[aff-man]

hmmmm sounds like shagged carbs

[FROSTY:Me]

what do the plugs look like? This could indicate how its running.

and have you checked the fuel lines for cracks, or the fuel filter?

Possibly also the ignitor box has issues too...

mg I diddnt think of that--the ignitor box that is --wonder If i can borrow one from a wrecker for a couple of minutes

[FROSTY:Me]

any other ideas guys--Im open to any suggestions.

[FzerozeroT]

I was going to drop the needles one notch but it has non adjustable needles so i can only raise em.

can anyone else see the prob there? Or are you talking about raising the needle using a spacer washer under the circlip of the needles?

does it have 4 carbs? you could try blanking off all but one and then rev to hear response, try with all carbs to see ifthey are all the same, maybe one carb/cylinder isn't doing anything till high revs (fuel or spark(individual coils?)), then concentrate on that one.

[White trash]

Frosty, I'm not trying to teach you how to suck eggs or anything but, what condition is the battery in?

With running problems like that, it's always the last thing people check.

[FROSTY:Me]

Ya know I dunno--But it seems to be cranking the bike over at pace and the spark at number 4 seems to be decent.
Don't worry about sucking eggs dude -If someone points out the blatent stuff to me --hey I mighta missed it.
-There was a time working on a honda -couldnt get the damb thing to run
cranked the battery down flat -then my ex said-um--what does this do--pointing to the kill switch--in the OFF position.

[FROSTY:Me]

[QUOTE=FzerozeroT]can anyone else see the prob there? Or are you talking about raising the needle using a spacer washer under the circlip of the needles?

yep--you can raise the needles by putting spacer washers--ya can't lower em because they dont have circlips. I was told The mounting plate could be machined to the thickness of a washer

[FROSTY:Me]

anyone else got bright ideas

[madandy]

sounds like an air and fuel issue to me.I know very little about 4 carb bikes but there may be some restriction to fuel at low revs or too much air in the mix.
Does it start sweet(smootly) and idle ok?

[What?]

Float heights too high - flooding until it starts using heaps of gas?
Check voltage supply to ignition module - maybe low volts until the motor is screaming?

[danb]

Speaking if this kind of stuff.
WARNING: I’m a noob @ bikes so don’t take this seriously if im wrong...
Check if any tubes are loose..
My bloody car was only running on 3 cylinders.
Found a stupid little vacuum pipe that goes to a temperature valve for the winter conditions for the hot air off the exhaust manifold had come loose and was sucking in too much air etc. The car would run ok at hight revs but harsh on the lower.

GOD I don’t know bloody cars.....