ZR550 dropping a cylinder - strange one - please read.

[ZephyrJoe]

Hi All

I searched for similar threads first but couldn't find anything to exactly match my problem:

Well, my Kawa ZR550 was running perfectly nicely on Saturday. I started her up on Sunday and on choke she seemed a bit lumpy, but once warmed a little she was fine. Put her in gear, bit of revs but as soon as I let the choke out she dropped a cylinder!

I've changed the HT leads for new but not caps (no spares and now bank holiday ggrrr) and plugs are only a month old. I did swap two at a time for good spare ones I have, in case one of the new plugs was a bad one, but this made no difference.

It was a very rainy night overnight Sat/Sun - so what could the rain have done to bring this issue on so sudden?? If it wasn't the rain what was it??

Please note that whether I pull off under 2k revs of pull off hard at 7k revs, as soon as the clutch is out it drops a cylinder. I can be riding along at below 2k or push it up to 5k and it will still run equally on 3 cylinders.

I've tried her again today - idles on all four, but still drops a cylinder as soon as the clutch is let off. Plugs were a little wet with petrol when pulled, no other fouling.

Any ideas people?

The side stand has been bypassed by cutting and joining the two wires. What would happen if rain got to the metal wires?

Cheers ZJ

[Stonefly]

Interesting problem!
I had EXACTLY the same issue with a GT750 P5 Kwak in the late 90's.
I tried everything i could possibly think of, but never managed to trace the fault. I was ready to push the fucker into a disused quarry when a mate asked if wanted a complete wiring loom for a P5.
I bought the loom for the princely sum of a tenner, fitted it, and the problem went away, never to return.
Now, i don't know whether the new loom cured it, or the physical act of replacing it dislodged some corrosion on a connecter. I recall there were a few connecters with powdery blue/green corrosion, which I cleaned and treated to a blob of petroleum jelly.
I know it sounds pretty drastic, but it may be worth removing your wiring loom completely, cleaning every single connecter and blobbing with petroleum jelly as you reconnect it all.
____________________
Current......Kawasaki ZZR1200 C2H and Kawasaki ZZR600 E7
Previous....Yamaha FS1E, Honda SS50, Suzuki AP50, BSA Bantam D14, Honda CD175, Honda CB250N, Kawasaki Z250A3, Yamaha RD250E, Kawasaki Z400, Kawasaki Z500, Kawasaki GPz550, Honda NTV600, Kawasaki GT750, Kawasaki Z1000R, Kawasaki GPX250

[ZephyrJoe]

Thanks for your reply Stonefly.

I've got the multimeter out to have a stab at testing the plug caps and three measured at 5.13-5.17 ohms and one measured at 4.73.

According to various sites on the tinterweb it seems that 5ohm caps have a +/-5% limit, so 4.73 is on the absolute limit and with the resistor plugs I guess it explains why it might drop a cylinder when under load.

However, I'm not sure because all 4 plugs are wet after idling on 4 cylinders for 5 mins or so - my thoughts are heading towards a dodgy cdi unit or the other black box parked behing it. I'll see what a new cap does...

After that I'll get a new coil and see if one has half broken down.

Failing that I'll sell the bugger again because the previous owner said this bike has been looked after and so far I can't see any evidence of that. After a month of ownership I've hardly ridden it, and I need a bike I can ride! The last 4 cylinder I got broke down after a month too! I've always preferred twins and I think I should've gone for a 500cc twin now.

I really don't want to be replacing the loom... even if it easy, I haven't built a good enough relationship with this bike to have the inclination to bother with something like that

[Casper]

Where is your choke? If bar or dash mounted you could be pulling a cable as you use it. Saying that i would have thought you would lose two cylinders but you never know. If you have the shitty cheap HT leads you could also have a crack and losing spark. Next time it does it try the drain bolt on the carb to the dead cylinder. If the fuel stops then you have a fulling issue at the neddle or that carb fuel feed pipe. If it does not stop running take the plug out and if bone dry you will need to strip and clean the jets in that carb. Also have a close look at the diaphgrams (If that is spelt right) swap thm about and see if the problem shifts to another cylinder, if so you may have a hole in one.

[ZephyrJoe]

I swapped the leads yesterday for new lead I had but it made no difference.

All choke, throttle and clutch cables are less than a month old and I have checked they are all free and not catching or getting stuck etc, to rule them out.

I don't know which cylinder is dropping out as it only happens when I let the clutch off, and all exhausts feel equally as hot when I stop.

I've just plodded the bike round the corner to a fellow bike club member's house, because he had a spare plug cap, tested and it was showing just over 5ohms and even though it lifted the idle revs a bit it still dropped a cylinder as I pulled off from his house.

When I got home I splashed puddle water on each downpipe (raining again...), and the outside two are definitely hotter than the middle two, although you wouldn't tell by putting your hand by them.

I'm ordering new coils and plug caps in a bit to rule them out. I'll keep the thread updated in case anyone else has this issue. There's surprisingly very little info on the net of such an issue so it must be rare.

[nightshaddow]

disconnect the coils and reconnect them, under load sounds like one may be braking down, i had a similar problem with a single cylinder engine would idle and rev to around 7k fine any further it would drop out and sound rough as hell,

corrosion on the plug was the cause fixed in 30 seconds (once i found it )
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"WHAT DO YOU MEAN 100 MPH THATS IMPOSSIBLE Its chinese OFFICER."
Current rides CB 125 TDE(the next project) NS125RK ( now on the road ) CB125TDC (soon to be project 17) melody ( the nephews )

[ZephyrJoe]