ZX 9 still running rough.

Basically since I bought my ZX9 it has had a rough idle and has ran rough at low rpms.

I have had the valves checked and adjusted. Carbs cleaned and balanced, twice. All mixture screws have been adjusted per the manual and there are no noticeable split or cracked hoses anywhere. Plugs have been changed, so has oil / air filters, oil and the battery checks out but it still runs rough to the point that cruising at anything below 40 - 50mph is almost unrideable.

I'm ready to give up on this bike now as I have no idea where else to look? My next option is simply to buy / borrow another set of carbs to see if that cures the problem to help[ narrow down what the cause is.

Any ideas on where to start looking would be very much appreciated. Thanks

Originally Posted by Dunn-y

Basically since I bought my ZX9 it has had a rough idle and has ran rough at low rpms.

I have had the valves checked and adjusted. Carbs cleaned and balanced, twice. All mixture screws have been adjusted per the manual and there are no noticeable split or cracked hoses anywhere. Plugs have been changed, so has oil / air filters, oil and the battery checks out but it still runs rough to the point that cruising at anything below 40 - 50mph is almost unrideable.

I'm ready to give up on this bike now as I have no idea where else to look? My next option is simply to buy / borrow another set of carbs to see if that cures the problem to help[ narrow down what the cause is.

Any ideas on where to start looking would be very much appreciated. Thanks

You have done all of the obvious things. My next step would be the plug caps/HT leads as any short here could cause rough running which may disappear as more fuel is delivered. After that would be coils. Good luck.

Check for vacuum leaks around the carb mounting boots?

The rubbers look good, no noticeable cracks and look like they are sealing properly. Will have to check the coils next.

Anything else I can check? It's only at constant throttle below 4000rpm and idles rough. Give it more throttle and it just pulls smoothly, no hesitation or spluttering.

Sounds like the pilot jets are still blocked or the emmulsion tubes are worn.

Ideally run it on a dyno and you will soon see if its fuel or electrical.

Get some carb/brake cleaner or easy start too, spray it around the carbs/inlet area. If it's an air leak, revs will rise. This will eliminate that possiblity straight away.

I sprayed some carb cleaner around the carb boots when it was idling and there was no noticeable change in the revs so I don't think it's a leak there.

What I have noticed is that if I rev it slightly, maybe to 3 - 4000rpm the revs drop below idle then raise back up. The mixture screws were set to 2 turns out which is what was recommended. They are now 1.5 turns out and it still does it. Not sure if this could help narrow down what the problem is.

I'm due a valve clearance check now (4000 miles since they were last changed) so I might as well just strip everything off it and triple check all hoses for cracks or splits and give everything another clean.

Never checked valves before so this should be interesting.

Not sure if relevant but I also loosened the bolts for the TPS and with the idle at 2000rpm there was no change in the idle speed when I moved the TPS to different positions. Reset it back to how it was now but I thought adjusting the TPS would have some effect on the idle speed.

[Red Herring]

Blocked/gummed up pilot jets seem to be getting more and more common place, especially if the bike has been sat for any period of time. It took me three attempts to clear some recently on a 600 Hornet. You need to do more than just remove them and blow through with lung power. Soak the passage ways for several minutes in carb cleaner and if you can pull a wire out of a wire brush they make quite effective "agitators" that you can use to prod gently inside, and then give it a proper blast through in both directions with compressed air. Don't forget to do the same with the emulsion tubes but be careful with the wire as some have a "cross" in the middle of the tube.

[yorkie_chris]

Originally Posted by Dunn-y

What I have noticed is that if I rev it slightly, maybe to 3 - 4000rpm the revs drop below idle then raise back up. The mixture screws were set to 2 turns out which is what was recommended. They are now 1.5 turns out and it still does it. Not sure if this could help narrow down what the problem is.

That is usually a sign of rich running. Sticky chokes or incorrect float heights.

After riding it again today it does feel and sound as though it is misfiring / stumbling.

Will give all the jets and carbs a good soak over the weekend and adjust the float heights. Don't think it's the choke but I'll double check that as well.

Thanks for all your suggestions. I'll let you know how it all goes.