ZXR750 still ruff

[99coconuts]

hey all, well, got the beast to run, but even after a new set of plugs and spraying a bunch of carb cleaner through it, its still ruff as guts. i have kind of an idea what it is tho, it seems the first cylinder is firing very little or not at all. the exhaust on that cylinder iswarm, i can hold my finger on it for a little bit where all the others sizzle up h20 in a flash.

now that cylinder DEFINATELY has good spark and i even tried swapping a plug over with #2. i also stuck my finger in the plug holes of 1&2 and they feel the same (no compression tester here so thats as high tech as i can be) and the suction feels the same with those two aswell when i have my hand over the carbs.

basically, this leads me to think timing, 3 cylinders firing, but firing rough, and backfiring aswell when shoved over 4-5000 rpm. only thing is, i have NO idea how to do the timing on a bike. would anyone here have some idea how to do it and the settings it should be on?

i'm beginning to think a manual might be more than just a good idea

[mike-s]

there are 3 things needed for combustion, fuel, air and spark.

you have compression (presumably), now would be the time to get yourself a ignition tester (basically a $5 doodad that has a coil of wire in it that picks up the energy from a RF pulse and uses it to light up a neon bulb) and see if it is actually sparking under load. you never know, it could be a loose connector and i severely doubt it to be a timing issue. That leaves fuel, have you tried draining the fuel from the car bowls, also check the tubing to make sure that it's getting the fuel fed correctly to it.

[greenman43]

I once say a dodgy HT lead (runs between the plug cap and the coil) arcing over to a cam bolt ; as a suggestion, take off your tank (and possibly the airbox if you can't see the leads clearly), and give the bike a good rev. Any shorting will be come obvious, either in short sparks or in a clicking sounds.

Just remembered, I'm pretty sure I have a spare Kawasaki J workshop manual at home ; if you're interested I can check tonight.

Cheers,
Brian

[James]

Hey Dale,

Have you tried emptying the tank and using new fuel? And make sure its not that Optimax crap - its no good (probably thats whats in it now!). If the bike sat for a while before you bought it and was regualrly warmed up on the choke, the Optimax wouldve stuffed your plugs. The amount of times bikes would come into the dealership running all dodgy-like simply because of fuel.

[99coconuts]

thanks guys, tank is off more often than its on at the moment i cant see any shorting anywhere so i doubt its that. and the fuel is new, the tank was near empty when i got it so its got a fresh $5 of premium unleaded in it. and yeah, i'm well aware of the need to stay away from optimax, it took almost a whole tank to clear up my old bandit when i rant it on that

thanks for your help so far guys, i've got a manual coming my way that i bought off ebay so hopefully with a bit of help from that, i'll be able to sort this mess out

[Jonno]

Do the above at dark, all may become clearer
Try new plugs.

[Jube]

Can't be the timing as the coil fires two plugs at once, i'd go for a blocked compensator tube in the carbs. Is the problem while stationary or while riding or worse one way or the other.